The Search for Extraterrestrial Intelligence (SETI) aims to find evidence of technosignatures, which
can point towards the possible existence of technologically advanced extraterrestrial life. Radio signals
similar to those engineered on Earth may be transmitted by other civilizations, motivating technosignature searches across the entire radio spectrum. In this endeavor, the low-frequency radio band
has remained largely unexplored; with prior radio searches primarily above 1 GHz. In this survey at
110 − 190 MHz, observations of 1,631,198 targets from TESS and Gaia are reported. Observations
took place simultaneously with two international stations (non-interferometric) of the Low Frequency
Array in Ireland and Sweden. We can reject the presence of any Doppler drifting narrow-band transmissions in the barycentric frame of reference, with equivalent isotropic radiated power of 1017 W, for
0.4 million (or 1.3 million) stellar systems at 110 (or 190) MHz. This work demonstrates the effectiveness of using multi-site simultaneous observations for rejecting anthropogenic signals in the search for
technosignatures.
A Search for Technosignatures Around 11,680 Stars with the Green Bank Telesco...Sérgio Sacani
We conducted a search for narrowband radio signals over four observing sessions in 2020–2023 with
the L-band receiver (1.15–1.73 GHz) of the 100 m diameter Green Bank Telescope. We pointed the
telescope in the directions of 62 TESS Objects of Interest, capturing radio emissions from a total of
∼11,860 stars and planetary systems in the ∼9 arcminute beam of the telescope. All detections were
either automatically rejected or visually inspected and confirmed to be of anthropogenic nature. In
this work, we also quantified the end-to-end efficiency of radio SETI pipelines with a signal injection
and recovery analysis. The UCLA SETI pipeline recovers 94.0% of the injected signals over the usable
frequency range of the receiver and 98.7% of the injections when regions of dense RFI are excluded. In
another pipeline that uses incoherent sums of 51 consecutive spectra, the recovery rate is ∼15 times
smaller at ∼6%. The pipeline efficiency affects SETI search volume calculations as well as calculations
of upper bounds on the number of transmitting civilizations. We developed an improved Drake Figure
of Merit for SETI search volume calculations that includes the pipeline efficiency and frequency drift
rate coverage. Based on our observations, we found that there is a high probability (94.0–98.7%) that
fewer than ∼0.014% of stars earlier than M8 within 100 pc host a transmitter that is detectable in
our search (EIRP > 1012 W). Finally, we showed that the UCLA SETI pipeline natively detects the
signals detected with AI techniques by Ma et al. (2023).
First light of VLT/HiRISE: High-resolution spectroscopy of young giant exopla...Sérgio Sacani
A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of
their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation
and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed
to leverage the capabilities of existing instruments that offer either high contrast imaging or high dispersion spectroscopy, by coupling them using
optical fibers. In this work we present the implementation and first on-sky results of the HiRISE instrument at the very large telescope (VLT),
which combines the exoplanet imager SPHERE with the recently upgraded high resolution spectrograph CRIRES using single-mode fibers. The
goal of HiRISE is to enable the characterization of known companions in the H band, at a spectral resolution of the order of R = λ/∆λ = 100 000,
in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three
major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance
of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we
detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak
value of ∼3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to
illustrate its potential.
Detection of an atmosphere around the super earth 55 cancri eSérgio Sacani
We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near
infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent
star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness
of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length
and a very high scanning speed. We use our specialized pipeline to take into account systematics
introduced by these observational parameters when coupled with the geometrical distortions of the
instrument. We measure the transit depth per wavelength channel with an average relative uncertainty
of 22 ppm per visit and nd modulations that depart from a straight line model with a 6 condence
level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably
hydrogen-rich. Our fully Bayesian spectral retrieval code, T -REx, has identied HCN to be the
most likely molecular candidate able to explain the features at 1.42 and 1.54 m. While additional
spectroscopic observations in a broader wavelength range in the infrared will be needed to conrm
the HCN detection, we discuss here the implications of such result. Our chemical model, developed
with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a
high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic
than previously thought.
An excess of_dusty_starbusts_related_to_the_spiderweb_galaxySérgio Sacani
Artigo que descreve as últimas observações do APEX revelando como se dá a formação de estrelas e a construção do Aglomerado de Galáxias da Teia de Aranha.
An excess of dusty starbursts related to the Spiderweb galaxyGOASA
This document summarizes a study that used the LABOCA instrument on the APEX telescope to observe a field around the high-redshift radio galaxy MRC1138-262 at z=2.16. 16 submillimeter galaxies (SMGs) were detected in the field, with fluxes between 3-11 mJy, indicating a density up to 4 times higher than blank field surveys. Photometric redshifts using Herschel, Spitzer, and VLT data show that at least 8 of the SMGs have z~2.2 and are part of the protocluster associated with MRC1138-262. This corresponds to a star formation rate density 1500 times higher than blank fields at this redshift, concentrated
A population of_fast_radio_bursts_ar_cosmological_distancesSérgio Sacani
1) Four fast radio bursts (FRBs) lasting only a few milliseconds were detected in a radio survey of the high Galactic latitude sky.
2) The bursts' properties indicate they are of celestial rather than terrestrial origin and likely originate from cosmological distances of 0.5 to 3 billion light years.
3) No coincident x-ray or gamma-ray signals were found associated with the bursts. Characterizing the population of FRBs could help determine the baryonic content of the universe.
This document presents a study characterizing active galactic nuclei (AGN) selected using mid-infrared colors from the Wide-field Infrared Survey Explorer (WISE). The authors find that a simple color criterion of W1-W2 ≥ 0.8 selects AGN with high reliability to a depth of W2 ∼ 15.0, identifying over 60 AGN candidates per square degree. This WISE selection method is effective at identifying both obscured and unobscured AGN. Using deep data in the COSMOS field, the authors explore the properties and redshift distribution of WISE-selected AGN candidates, finding the selection identifies 78% of AGN identified by previous Spitzer studies.
This document describes observations of the Seyfert 1 galaxy Mrk 509 using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). The observations detected absorption features in the ultraviolet spectrum, which are attributed to outflowing gas from the active galactic nucleus as well as gas in the galaxy's interstellar medium and halo. The COS observations provide higher signal-to-noise and resolution than previous observations, detecting additional complexity in the absorption features. Variability in some features constrains the distances of absorbing gas components to be less than 250 pc and 1.5 kpc from the active nucleus. The absorption lines only partially cover the emission from the active nucleus, possibly due to
A Search for Technosignatures Around 11,680 Stars with the Green Bank Telesco...Sérgio Sacani
We conducted a search for narrowband radio signals over four observing sessions in 2020–2023 with
the L-band receiver (1.15–1.73 GHz) of the 100 m diameter Green Bank Telescope. We pointed the
telescope in the directions of 62 TESS Objects of Interest, capturing radio emissions from a total of
∼11,860 stars and planetary systems in the ∼9 arcminute beam of the telescope. All detections were
either automatically rejected or visually inspected and confirmed to be of anthropogenic nature. In
this work, we also quantified the end-to-end efficiency of radio SETI pipelines with a signal injection
and recovery analysis. The UCLA SETI pipeline recovers 94.0% of the injected signals over the usable
frequency range of the receiver and 98.7% of the injections when regions of dense RFI are excluded. In
another pipeline that uses incoherent sums of 51 consecutive spectra, the recovery rate is ∼15 times
smaller at ∼6%. The pipeline efficiency affects SETI search volume calculations as well as calculations
of upper bounds on the number of transmitting civilizations. We developed an improved Drake Figure
of Merit for SETI search volume calculations that includes the pipeline efficiency and frequency drift
rate coverage. Based on our observations, we found that there is a high probability (94.0–98.7%) that
fewer than ∼0.014% of stars earlier than M8 within 100 pc host a transmitter that is detectable in
our search (EIRP > 1012 W). Finally, we showed that the UCLA SETI pipeline natively detects the
signals detected with AI techniques by Ma et al. (2023).
First light of VLT/HiRISE: High-resolution spectroscopy of young giant exopla...Sérgio Sacani
A major endeavor of this decade is the direct characterization of young giant exoplanets at high spectral resolution to determine the composition of
their atmosphere and infer their formation processes and evolution. Such a goal represents a major challenge owing to their small angular separation
and luminosity contrast with respect to their parent stars. Instead of designing and implementing completely new facilities, it has been proposed
to leverage the capabilities of existing instruments that offer either high contrast imaging or high dispersion spectroscopy, by coupling them using
optical fibers. In this work we present the implementation and first on-sky results of the HiRISE instrument at the very large telescope (VLT),
which combines the exoplanet imager SPHERE with the recently upgraded high resolution spectrograph CRIRES using single-mode fibers. The
goal of HiRISE is to enable the characterization of known companions in the H band, at a spectral resolution of the order of R = λ/∆λ = 100 000,
in a few hours of observing time. We present the main design choices and the technical implementation of the system, which is constituted of three
major parts: the fiber injection module inside of SPHERE, the fiber bundle around the telescope, and the fiber extraction module at the entrance
of CRIRES. We also detail the specific calibrations required for HiRISE and the operations of the instrument for science observations. Finally, we
detail the performance of the system in terms of astrometry, temporal stability, optical aberrations, and transmission, for which we report a peak
value of ∼3.9% based on sky measurements in median observing conditions. Finally, we report on the first astrophysical detection of HiRISE to
illustrate its potential.
Detection of an atmosphere around the super earth 55 cancri eSérgio Sacani
We report the analysis of two new spectroscopic observations of the super-Earth 55 Cancri e, in the near
infrared, obtained with the WFC3 camera onboard the HST. 55 Cancri e orbits so close to its parent
star, that temperatures much higher than 2000 K are expected on its surface. Given the brightness
of 55 Cancri, the observations were obtained in scanning mode, adopting a very long scanning length
and a very high scanning speed. We use our specialized pipeline to take into account systematics
introduced by these observational parameters when coupled with the geometrical distortions of the
instrument. We measure the transit depth per wavelength channel with an average relative uncertainty
of 22 ppm per visit and nd modulations that depart from a straight line model with a 6 condence
level. These results suggest that 55 Cancri e is surrounded by an atmosphere, which is probably
hydrogen-rich. Our fully Bayesian spectral retrieval code, T -REx, has identied HCN to be the
most likely molecular candidate able to explain the features at 1.42 and 1.54 m. While additional
spectroscopic observations in a broader wavelength range in the infrared will be needed to conrm
the HCN detection, we discuss here the implications of such result. Our chemical model, developed
with combustion specialists, indicates that relatively high mixing ratios of HCN may be caused by a
high C/O ratio. This result suggests this super-Earth is a carbon-rich environment even more exotic
than previously thought.
An excess of_dusty_starbusts_related_to_the_spiderweb_galaxySérgio Sacani
Artigo que descreve as últimas observações do APEX revelando como se dá a formação de estrelas e a construção do Aglomerado de Galáxias da Teia de Aranha.
An excess of dusty starbursts related to the Spiderweb galaxyGOASA
This document summarizes a study that used the LABOCA instrument on the APEX telescope to observe a field around the high-redshift radio galaxy MRC1138-262 at z=2.16. 16 submillimeter galaxies (SMGs) were detected in the field, with fluxes between 3-11 mJy, indicating a density up to 4 times higher than blank field surveys. Photometric redshifts using Herschel, Spitzer, and VLT data show that at least 8 of the SMGs have z~2.2 and are part of the protocluster associated with MRC1138-262. This corresponds to a star formation rate density 1500 times higher than blank fields at this redshift, concentrated
A population of_fast_radio_bursts_ar_cosmological_distancesSérgio Sacani
1) Four fast radio bursts (FRBs) lasting only a few milliseconds were detected in a radio survey of the high Galactic latitude sky.
2) The bursts' properties indicate they are of celestial rather than terrestrial origin and likely originate from cosmological distances of 0.5 to 3 billion light years.
3) No coincident x-ray or gamma-ray signals were found associated with the bursts. Characterizing the population of FRBs could help determine the baryonic content of the universe.
This document presents a study characterizing active galactic nuclei (AGN) selected using mid-infrared colors from the Wide-field Infrared Survey Explorer (WISE). The authors find that a simple color criterion of W1-W2 ≥ 0.8 selects AGN with high reliability to a depth of W2 ∼ 15.0, identifying over 60 AGN candidates per square degree. This WISE selection method is effective at identifying both obscured and unobscured AGN. Using deep data in the COSMOS field, the authors explore the properties and redshift distribution of WISE-selected AGN candidates, finding the selection identifies 78% of AGN identified by previous Spitzer studies.
This document describes observations of the Seyfert 1 galaxy Mrk 509 using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST). The observations detected absorption features in the ultraviolet spectrum, which are attributed to outflowing gas from the active galactic nucleus as well as gas in the galaxy's interstellar medium and halo. The COS observations provide higher signal-to-noise and resolution than previous observations, detecting additional complexity in the absorption features. Variability in some features constrains the distances of absorbing gas components to be less than 250 pc and 1.5 kpc from the active nucleus. The absorption lines only partially cover the emission from the active nucleus, possibly due to
Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar ...Sérgio Sacani
Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs
modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial
correlation. Here we describe a search for an isotropic stochastic gravitational-wave background (GWB) using
observations of 30 millisecond pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA), which
spans 18 yr. Using current Bayesian inference techniques we recover and characterize a common-spectrum noise
process. Represented as a strain spectrum h Af c 1yr = -1 a ( ) , we measure A 3.1 10 0.9 = ´ 1.3 15 -
+ - and
α = −0.45 ± 0.20, respectively (median and 68% credible interval). For a spectral index of α = −2/3,
corresponding to an isotropic background of GWs radiated by inspiraling supermassive black hole binaries, we
recover an amplitude of A 2.04 10 0.22 = ´ 0.25 15 -
+ - . However, we demonstrate that the apparent signal strength is timedependent, as the first half of our data set can be used to place an upper limit on A that is in tension with the inferred
common-spectrum amplitude using the complete data set. We search for spatial correlations in the observations by
hierarchically analyzing individual pulsar pairs, which also allows for significance validation through randomizing
pulsar positions on the sky. For a process with α = −2/3, we measure spatial correlations consistent with a GWB,
with an estimated false-alarm probability of p 0.02 (approx. 2σ). The long timing baselines of the PPTA and the
access to southern pulsars will continue to play an important role in the International Pulsar Timing Array.
GOALS-JWST: Unveiling Dusty Compact Sources in the Merging Galaxy IIZw096Sérgio Sacani
We have used the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST) to obtain the first
spatially resolved, mid-infrared images of IIZw096, a merging luminous infrared galaxy (LIRG) at z = 0.036.
Previous observations with the Spitzer Space Telescope suggested that the vast majority of the total IR luminosity
(LIR) of the system originated from a small region outside of the two merging nuclei. New observations with
JWST/MIRI now allow an accurate measurement of the location and luminosity density of the source that is
responsible for the bulk of the IR emission. We estimate that 40%–70% of the IR bolometric luminosity, or
3–5 × 1011 Le, arises from a source no larger than 175 pc in radius, suggesting a luminosity density of at least
3–5 × 1012 Le kpc−2
. In addition, we detect 11 other star-forming sources, five of which were previously
unknown. The MIRI F1500W/F560W colors of most of these sources, including the source responsible for the
bulk of the far-IR emission, are much redder than the nuclei of local LIRGs. These observations reveal the power
of JWST to disentangle the complex regions at the hearts of merging, dusty galaxies.
Imaging the Milky Way with Millihertz Gravitational WavesSérgio Sacani
Modern astronomers enjoy access to all-sky images across a wide range of the electromagnetic spectrum from
long-wavelength radio to high-energy gamma rays. The most prominent feature in many of these images is our
own Galaxy, with different features revealed in each wave band. Gravitational waves (GWs) have recently been
added to the astronomers’ toolkit as a nonelectromagnetic messenger. To date, all identified GW sources have been
extra-Galactic and transient. However, the Milky Way hosts a population of ultracompact binaries (UCBs), which
radiate persistent GWs in the milliHertz band that is not observable with today’s terrestrial gravitational-wave
detectors. Space-based detectors such as the Laser Interferometer Space Antenna will measure this population and
provide a census of their location, masses, and orbital properties. In this work, we will show how this data can be
used to form a false-color image of the Galaxy that represents the intensity and frequency of the gravitational
waves produced by the UCB population. Such images can be used to study the morphology of the Galaxy, identify
interesting multimessenger sources through cross-matching, and for educational and outreach purposes.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
This document presents the target selection process for the first year of the Breakthrough Listen search for intelligent life using the Green Bank Telescope, Parkes Telescope, and Automated Planet Finder. The targets include: 1) The 60 nearest stars within 5.1 parsecs to search for faint signals; 2) 1649 stars spanning stellar types from the Hipparcos catalog; 3) 123 nearby galaxies representing different morphological types to search billions of stars simultaneously; and 4) several classes of exotic objects like white dwarfs and neutron stars. The telescopes will observe 1,000,000 stars and galaxies at radio and optical wavelengths between 350 MHz to 100 GHz and 374-950nm, respectively, to search for technological signals.
1. This paper presents results from a 600 ks XMM-Newton observation of Mrk 509 as part of a large multiwavelength campaign.
2. The high quality spectrum allows an unprecedented investigation of the ionized outflow through the detection of multiple absorption lines.
3. The outflow is found to consist of at least two velocity components that have been observed previously, as well as a tentative high velocity component. Discrete ionization components are detected spanning four orders of magnitude in ionization parameter.
Life, the Universe, andSETI in a NutshellSérgio Sacani
Todate,no
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ifeverybodyislistening,
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This document summarizes the results of infrared transmission spectroscopy of the exoplanets HD 209458b and XO-1b using the Hubble Space Telescope's Wide Field Camera 3 instrument. Key findings include:
- Both planets exhibited water absorption of approximately 200 ppm at the peak water absorption wavelength of 1.38 microns.
- The water absorption measured for XO-1b contradicts stronger absorption reported from previous observations using a different instrument.
- The weak water absorption measured for HD 209458b is consistent with previous observations of weak molecular absorption features for this planet.
- Model atmospheres including uniformly distributed extra opacity can approximately account for the water measurements as well as previous sodium absorption measurements for
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
This document summarizes the results of a 180 ks Chandra-LETGS observation of Mrk 509 as part of a larger multi-wavelength campaign. The observation detected several absorption features in the X-ray spectrum originating from an ionized absorber, including ions with three distinct ionization degrees. The lowest ionized component is slightly redshifted and not in pressure equilibrium with the others, likely belonging to the host galaxy's interstellar medium. The other two components are outflowing at velocities of around -200 and -455 km/s. Simultaneous HST-COS observations detected 13 UV kinematic components, and at least three can be associated with the X-ray components, providing evidence that the UV and X-
Radio beacon for ionspheric tomography RaBITKarlos Svoboda
This document presents preliminary results from the Radio Beacon for Ionospheric Tomography (RaBIT) payload onboard the YOUTHSAT satellite. RaBIT transmits signals at 150 and 400 MHz that are received by ground stations in India to generate tomographic images of the ionosphere. The first tomograms obtained using RaBIT data during the beginning of solar cycle 24 are shown, demonstrating its ability to investigate large-scale ionospheric structures over the Indian region like the equatorial ionization anomaly. RaBIT improves upon previous experiments by providing improved temporal coverage of the ionosphere from its orbit onboard YOUTHSAT.
O telescópio de rastreio VISTA do ESO encontrou uma horda de galáxias massivas anteriormente ocultas por poeira, que existiram quando o Universo era ainda bebê. Ao descobrir e estudar uma grande quantidade deste tipo de galáxias, os astrônomos descobriram, exatamente e pela primeira vez, quando é que tais monstros apareceram pela primeira vez no Universo.
O simples fato de contar o número de galáxias que existem em determinada área do céu permite aos astrônomos testar teorias de formação e evolução galática. No entanto, uma tarefa aparentemente tão fácil torna-se mais difícil quando tentamos contar galáxias cada vez mais distantes e tênues e é mais complicada ainda devido ao fato das galáxias mais brilhantes e fáceis de observar — as mais massivas no Universo — se tornarem mais raras à medida que os astrônomos observam o passado do Universo, enquanto que as galáxias menos brilhantes, mas muito mais numerosas, são ainda mais difíceis de detectar.
Uma equipe de astrônomos liderada por Karina Caputi do Instituto Astronômico Kapteyn da Universidade de Groningen, descobriu muitas galáxias distantes que não tinham sido detectadas anteriormente. A equipe utilizou imagens do rastreioUltraVISTA, um dos seis projetos que usam o VISTA para mapear o céu no infravermelho próximo, e fez um censo das galáxias tênues quando a idade do Universo estava compreendida entre 0,75 e 2,1 bilhões de anos.
This document summarizes VLBI observations of supernova SN 2011dh made 14 days after its discovery, providing the earliest radio image of a supernova. The observations detected SN 2011dh at 22 GHz using a subset of the EVN array. The recovered flux density was approximately half the value measured by the EVLA at the same frequency and epoch, possibly due to extended emission or calibration issues. Precise coordinates for SN 2011dh were determined, linked to the ICRF, which may help improve future VLBI observations of the supernova.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
The document discusses geospatial technology and geospatial data. Geospatial technology deals with techniques for geospatial data, which is data that includes information about locations on Earth, such as latitude and longitude. Some key techniques discussed are remote sensing using platforms like satellites and aircraft, as well as GIS for storing, manipulating and analyzing geospatial data from sources like GPS and remote sensing.
This document summarizes an observational study of 92 southern stars using near-infrared interferometry to search for hot exozodiacal dust. The study found an 11% detection rate of bright dust, with 9 confirmed and 3 tentative detections. The detection rate decreased for later spectral type stars and increased with stellar age. No correlation was found between the presence of cold dust and hot dust. Spectral analysis suggested the dust is extremely hot or emission is dominated by scattered light in most cases. The results provide insights into the prevalence and properties of dust near the habitable zones of other stars.
This summarizes a scientific study on long-distance quantum teleportation between two laboratories separated by 55 meters but connected by 2 kilometers of fiber optic cable. The key points are:
1) Researchers teleported quantum states (qubits) carried by photons at 1.3 micrometer wavelengths onto photons at 1.55 micrometer wavelengths between the two laboratories.
2) The qubits were encoded in time-bin superpositions and entanglement rather than polarization to make them more robust against decoherence in optical fibers.
3) A partial Bell state measurement was performed using linear optics at the receiving end to probabilistically teleport the quantum states over the long distance.
The muse 3_d_view_of_the_hubble_deep_field_southSérgio Sacani
Artigo mostra como foram as observações feitas com o MUSE, o novo instrumento do VLT do campo profundo do Hubble. Além de descobrir 20 novos objetos, o MUSE conseguiu medir as propriedades das galáxias e até representar as mais próximas em 3 dimensões.
XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Proto...Sérgio Sacani
This document presents the first results from the JWST XUE program, which observed 15 protoplanetary disks in the NGC 6357 star-forming region using MIRI. For the disk XUE 1, located near massive stars, the following was found:
1) Abundant water, CO, CO2, HCN, and C2H2 were detected in the inner few AU, indicating an oxygen-dominated gas-phase chemistry similar to isolated disks.
2) Small crystalline silicate dust is present at the disk surface.
3) The column densities and chemistry are surprisingly similar to isolated disks despite the extreme radiation environment, implying inner disks can retain conditions conducive to rocky planet
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
This document describes a public release of photometric redshifts and galaxy properties from multi-wavelength data in the Abell-2744 and MACS-J0416 galaxy cluster fields observed as part of the Frontier Fields program. Photometric redshifts were estimated using six different methods and have an accuracy of 3-5%. Accounting for gravitational lensing magnification, the H-band number counts agree with CANDELS at bright magnitudes but extend to intrinsically fainter galaxies of H=32-33. The Frontier Fields data allow probing galaxy stellar masses 0.5-1.5 dex lower than in wide fields, including sources with masses of 107-108 solar masses at z>5. Star formation rates can be detected 1
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
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Search for an Isotropic Gravitational-wave Background with the Parkes Pulsar ...Sérgio Sacani
Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs
modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial
correlation. Here we describe a search for an isotropic stochastic gravitational-wave background (GWB) using
observations of 30 millisecond pulsars from the third data release of the Parkes Pulsar Timing Array (PPTA), which
spans 18 yr. Using current Bayesian inference techniques we recover and characterize a common-spectrum noise
process. Represented as a strain spectrum h Af c 1yr = -1 a ( ) , we measure A 3.1 10 0.9 = ´ 1.3 15 -
+ - and
α = −0.45 ± 0.20, respectively (median and 68% credible interval). For a spectral index of α = −2/3,
corresponding to an isotropic background of GWs radiated by inspiraling supermassive black hole binaries, we
recover an amplitude of A 2.04 10 0.22 = ´ 0.25 15 -
+ - . However, we demonstrate that the apparent signal strength is timedependent, as the first half of our data set can be used to place an upper limit on A that is in tension with the inferred
common-spectrum amplitude using the complete data set. We search for spatial correlations in the observations by
hierarchically analyzing individual pulsar pairs, which also allows for significance validation through randomizing
pulsar positions on the sky. For a process with α = −2/3, we measure spatial correlations consistent with a GWB,
with an estimated false-alarm probability of p 0.02 (approx. 2σ). The long timing baselines of the PPTA and the
access to southern pulsars will continue to play an important role in the International Pulsar Timing Array.
GOALS-JWST: Unveiling Dusty Compact Sources in the Merging Galaxy IIZw096Sérgio Sacani
We have used the Mid-InfraRed Instrument (MIRI) on the James Webb Space Telescope (JWST) to obtain the first
spatially resolved, mid-infrared images of IIZw096, a merging luminous infrared galaxy (LIRG) at z = 0.036.
Previous observations with the Spitzer Space Telescope suggested that the vast majority of the total IR luminosity
(LIR) of the system originated from a small region outside of the two merging nuclei. New observations with
JWST/MIRI now allow an accurate measurement of the location and luminosity density of the source that is
responsible for the bulk of the IR emission. We estimate that 40%–70% of the IR bolometric luminosity, or
3–5 × 1011 Le, arises from a source no larger than 175 pc in radius, suggesting a luminosity density of at least
3–5 × 1012 Le kpc−2
. In addition, we detect 11 other star-forming sources, five of which were previously
unknown. The MIRI F1500W/F560W colors of most of these sources, including the source responsible for the
bulk of the far-IR emission, are much redder than the nuclei of local LIRGs. These observations reveal the power
of JWST to disentangle the complex regions at the hearts of merging, dusty galaxies.
Imaging the Milky Way with Millihertz Gravitational WavesSérgio Sacani
Modern astronomers enjoy access to all-sky images across a wide range of the electromagnetic spectrum from
long-wavelength radio to high-energy gamma rays. The most prominent feature in many of these images is our
own Galaxy, with different features revealed in each wave band. Gravitational waves (GWs) have recently been
added to the astronomers’ toolkit as a nonelectromagnetic messenger. To date, all identified GW sources have been
extra-Galactic and transient. However, the Milky Way hosts a population of ultracompact binaries (UCBs), which
radiate persistent GWs in the milliHertz band that is not observable with today’s terrestrial gravitational-wave
detectors. Space-based detectors such as the Laser Interferometer Space Antenna will measure this population and
provide a census of their location, masses, and orbital properties. In this work, we will show how this data can be
used to form a false-color image of the Galaxy that represents the intensity and frequency of the gravitational
waves produced by the UCB population. Such images can be used to study the morphology of the Galaxy, identify
interesting multimessenger sources through cross-matching, and for educational and outreach purposes.
1. This document describes a multiwavelength campaign on the Seyfert 1 galaxy Mrk 509 using five satellites and two ground-based facilities.
2. The campaign aims to study several open questions about active galactic nuclei (AGN), including the location and physics of outflows from AGN, the nature of continuum emission, the geometry and physical state of the X-ray broad emission line region, and the Fe-K line complex.
3. The observations cover more than five decades in frequency, from 2 μm to 200 keV, and include a simultaneous set of deep XMM-Newton and INTEGRAL observations over seven weeks. This allows the authors to disentangle different components and study time variability
This document presents the target selection process for the first year of the Breakthrough Listen search for intelligent life using the Green Bank Telescope, Parkes Telescope, and Automated Planet Finder. The targets include: 1) The 60 nearest stars within 5.1 parsecs to search for faint signals; 2) 1649 stars spanning stellar types from the Hipparcos catalog; 3) 123 nearby galaxies representing different morphological types to search billions of stars simultaneously; and 4) several classes of exotic objects like white dwarfs and neutron stars. The telescopes will observe 1,000,000 stars and galaxies at radio and optical wavelengths between 350 MHz to 100 GHz and 374-950nm, respectively, to search for technological signals.
1. This paper presents results from a 600 ks XMM-Newton observation of Mrk 509 as part of a large multiwavelength campaign.
2. The high quality spectrum allows an unprecedented investigation of the ionized outflow through the detection of multiple absorption lines.
3. The outflow is found to consist of at least two velocity components that have been observed previously, as well as a tentative high velocity component. Discrete ionization components are detected spanning four orders of magnitude in ionization parameter.
Life, the Universe, andSETI in a NutshellSérgio Sacani
Todate,no
SETI
observing
program
hassucceededindetectinganyunambiguousevidenceofan
extraterrestrial
technology.Regrettably,
this
paper
willtherefore
not
dazzleyou
with
the
analysisof
the
contentsofanyinterstellarmessages.However,asis
appropriate
foraplenarypresentation,
this
paper
doesprovidean
update
on
the
state
of
SETI
programsworldwide.Itdiscusses
the
various flavors ofobservational
SETI
projectscurrentlyon
the
air,plansforfutureinstrumentation,recent
attempts
toproactively
plan
forsuccess,
andthe
prospectsforfuture
public/private
partnershipstofundtheseefforts.
Thepaper
concludes
with
some
tentative
responsesto
the What
ifeverybodyislistening,
and
nobodyis
transmitting?
query.
This document summarizes the results of infrared transmission spectroscopy of the exoplanets HD 209458b and XO-1b using the Hubble Space Telescope's Wide Field Camera 3 instrument. Key findings include:
- Both planets exhibited water absorption of approximately 200 ppm at the peak water absorption wavelength of 1.38 microns.
- The water absorption measured for XO-1b contradicts stronger absorption reported from previous observations using a different instrument.
- The weak water absorption measured for HD 209458b is consistent with previous observations of weak molecular absorption features for this planet.
- Model atmospheres including uniformly distributed extra opacity can approximately account for the water measurements as well as previous sodium absorption measurements for
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
This document summarizes the results of a 180 ks Chandra-LETGS observation of Mrk 509 as part of a larger multi-wavelength campaign. The observation detected several absorption features in the X-ray spectrum originating from an ionized absorber, including ions with three distinct ionization degrees. The lowest ionized component is slightly redshifted and not in pressure equilibrium with the others, likely belonging to the host galaxy's interstellar medium. The other two components are outflowing at velocities of around -200 and -455 km/s. Simultaneous HST-COS observations detected 13 UV kinematic components, and at least three can be associated with the X-ray components, providing evidence that the UV and X-
Radio beacon for ionspheric tomography RaBITKarlos Svoboda
This document presents preliminary results from the Radio Beacon for Ionospheric Tomography (RaBIT) payload onboard the YOUTHSAT satellite. RaBIT transmits signals at 150 and 400 MHz that are received by ground stations in India to generate tomographic images of the ionosphere. The first tomograms obtained using RaBIT data during the beginning of solar cycle 24 are shown, demonstrating its ability to investigate large-scale ionospheric structures over the Indian region like the equatorial ionization anomaly. RaBIT improves upon previous experiments by providing improved temporal coverage of the ionosphere from its orbit onboard YOUTHSAT.
O telescópio de rastreio VISTA do ESO encontrou uma horda de galáxias massivas anteriormente ocultas por poeira, que existiram quando o Universo era ainda bebê. Ao descobrir e estudar uma grande quantidade deste tipo de galáxias, os astrônomos descobriram, exatamente e pela primeira vez, quando é que tais monstros apareceram pela primeira vez no Universo.
O simples fato de contar o número de galáxias que existem em determinada área do céu permite aos astrônomos testar teorias de formação e evolução galática. No entanto, uma tarefa aparentemente tão fácil torna-se mais difícil quando tentamos contar galáxias cada vez mais distantes e tênues e é mais complicada ainda devido ao fato das galáxias mais brilhantes e fáceis de observar — as mais massivas no Universo — se tornarem mais raras à medida que os astrônomos observam o passado do Universo, enquanto que as galáxias menos brilhantes, mas muito mais numerosas, são ainda mais difíceis de detectar.
Uma equipe de astrônomos liderada por Karina Caputi do Instituto Astronômico Kapteyn da Universidade de Groningen, descobriu muitas galáxias distantes que não tinham sido detectadas anteriormente. A equipe utilizou imagens do rastreioUltraVISTA, um dos seis projetos que usam o VISTA para mapear o céu no infravermelho próximo, e fez um censo das galáxias tênues quando a idade do Universo estava compreendida entre 0,75 e 2,1 bilhões de anos.
This document summarizes VLBI observations of supernova SN 2011dh made 14 days after its discovery, providing the earliest radio image of a supernova. The observations detected SN 2011dh at 22 GHz using a subset of the EVN array. The recovered flux density was approximately half the value measured by the EVLA at the same frequency and epoch, possibly due to extended emission or calibration issues. Precise coordinates for SN 2011dh were determined, linked to the ICRF, which may help improve future VLBI observations of the supernova.
AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offs...Sérgio Sacani
Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events
whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and
luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming
host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT,
AT 2023fhn. The Hubble Space Telescope data reveal a large offset (> 3.5 half-light radii) from the two closest galaxies, both
at redshift 𝑧 ∼ 0.24. The location of AT 2023fhn is in stark contrast with previous events, and demonstrates that LFBOTs can
occur in a range of galactic environments.
The document discusses geospatial technology and geospatial data. Geospatial technology deals with techniques for geospatial data, which is data that includes information about locations on Earth, such as latitude and longitude. Some key techniques discussed are remote sensing using platforms like satellites and aircraft, as well as GIS for storing, manipulating and analyzing geospatial data from sources like GPS and remote sensing.
This document summarizes an observational study of 92 southern stars using near-infrared interferometry to search for hot exozodiacal dust. The study found an 11% detection rate of bright dust, with 9 confirmed and 3 tentative detections. The detection rate decreased for later spectral type stars and increased with stellar age. No correlation was found between the presence of cold dust and hot dust. Spectral analysis suggested the dust is extremely hot or emission is dominated by scattered light in most cases. The results provide insights into the prevalence and properties of dust near the habitable zones of other stars.
This summarizes a scientific study on long-distance quantum teleportation between two laboratories separated by 55 meters but connected by 2 kilometers of fiber optic cable. The key points are:
1) Researchers teleported quantum states (qubits) carried by photons at 1.3 micrometer wavelengths onto photons at 1.55 micrometer wavelengths between the two laboratories.
2) The qubits were encoded in time-bin superpositions and entanglement rather than polarization to make them more robust against decoherence in optical fibers.
3) A partial Bell state measurement was performed using linear optics at the receiving end to probabilistically teleport the quantum states over the long distance.
The muse 3_d_view_of_the_hubble_deep_field_southSérgio Sacani
Artigo mostra como foram as observações feitas com o MUSE, o novo instrumento do VLT do campo profundo do Hubble. Além de descobrir 20 novos objetos, o MUSE conseguiu medir as propriedades das galáxias e até representar as mais próximas em 3 dimensões.
XUE: Molecular Inventory in the Inner Region of an Extremely Irradiated Proto...Sérgio Sacani
This document presents the first results from the JWST XUE program, which observed 15 protoplanetary disks in the NGC 6357 star-forming region using MIRI. For the disk XUE 1, located near massive stars, the following was found:
1) Abundant water, CO, CO2, HCN, and C2H2 were detected in the inner few AU, indicating an oxygen-dominated gas-phase chemistry similar to isolated disks.
2) Small crystalline silicate dust is present at the disk surface.
3) The column densities and chemistry are surprisingly similar to isolated disks despite the extreme radiation environment, implying inner disks can retain conditions conducive to rocky planet
The ASTRODEEP Frontier Fields catalogues II. Photometric redshifts and rest f...Sérgio Sacani
This document describes a public release of photometric redshifts and galaxy properties from multi-wavelength data in the Abell-2744 and MACS-J0416 galaxy cluster fields observed as part of the Frontier Fields program. Photometric redshifts were estimated using six different methods and have an accuracy of 3-5%. Accounting for gravitational lensing magnification, the H-band number counts agree with CANDELS at bright magnitudes but extend to intrinsically fainter galaxies of H=32-33. The Frontier Fields data allow probing galaxy stellar masses 0.5-1.5 dex lower than in wide fields, including sources with masses of 107-108 solar masses at z>5. Star formation rates can be detected 1
Similar to A Simultaneous dual-site technosignature search using international LOFAR stations (20)
Compositions of iron-meteorite parent bodies constrainthe structure of the pr...Sérgio Sacani
Magmatic iron-meteorite parent bodies are the earliest planetesimals in the Solar System,and they preserve information about conditions and planet-forming processes in thesolar nebula. In this study, we include comprehensive elemental compositions andfractional-crystallization modeling for iron meteorites from the cores of five differenti-ated asteroids from the inner Solar System. Together with previous results of metalliccores from the outer Solar System, we conclude that asteroidal cores from the outerSolar System have smaller sizes, elevated siderophile-element abundances, and simplercrystallization processes than those from the inner Solar System. These differences arerelated to the formation locations of the parent asteroids because the solar protoplane-tary disk varied in redox conditions, elemental distributions, and dynamics at differentheliocentric distances. Using highly siderophile-element data from iron meteorites, wereconstruct the distribution of calcium-aluminum-rich inclusions (CAIs) across theprotoplanetary disk within the first million years of Solar-System history. CAIs, the firstsolids to condense in the Solar System, formed close to the Sun. They were, however,concentrated within the outer disk and depleted within the inner disk. Future modelsof the structure and evolution of the protoplanetary disk should account for this dis-tribution pattern of CAIs.
Signatures of wave erosion in Titan’s coastsSérgio Sacani
The shorelines of Titan’s hydrocarbon seas trace flooded erosional landforms such as river valleys; however, it isunclear whether coastal erosion has subsequently altered these shorelines. Spacecraft observations and theo-retical models suggest that wind may cause waves to form on Titan’s seas, potentially driving coastal erosion,but the observational evidence of waves is indirect, and the processes affecting shoreline evolution on Titanremain unknown. No widely accepted framework exists for using shoreline morphology to quantitatively dis-cern coastal erosion mechanisms, even on Earth, where the dominant mechanisms are known. We combinelandscape evolution models with measurements of shoreline shape on Earth to characterize how differentcoastal erosion mechanisms affect shoreline morphology. Applying this framework to Titan, we find that theshorelines of Titan’s seas are most consistent with flooded landscapes that subsequently have been eroded bywaves, rather than a uniform erosional process or no coastal erosion, particularly if wave growth saturates atfetch lengths of tens of kilometers.
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Mechanisms and Applications of Antiviral Neutralizing Antibodies - Creative B...Creative-Biolabs
Neutralizing antibodies, pivotal in immune defense, specifically bind and inhibit viral pathogens, thereby playing a crucial role in protecting against and mitigating infectious diseases. In this slide, we will introduce what antibodies and neutralizing antibodies are, the production and regulation of neutralizing antibodies, their mechanisms of action, classification and applications, as well as the challenges they face.
CLASS 12th CHEMISTRY SOLID STATE ppt (Animated)eitps1506
Description:
Dive into the fascinating realm of solid-state physics with our meticulously crafted online PowerPoint presentation. This immersive educational resource offers a comprehensive exploration of the fundamental concepts, theories, and applications within the realm of solid-state physics.
From crystalline structures to semiconductor devices, this presentation delves into the intricate principles governing the behavior of solids, providing clear explanations and illustrative examples to enhance understanding. Whether you're a student delving into the subject for the first time or a seasoned researcher seeking to deepen your knowledge, our presentation offers valuable insights and in-depth analyses to cater to various levels of expertise.
Key topics covered include:
Crystal Structures: Unravel the mysteries of crystalline arrangements and their significance in determining material properties.
Band Theory: Explore the electronic band structure of solids and understand how it influences their conductive properties.
Semiconductor Physics: Delve into the behavior of semiconductors, including doping, carrier transport, and device applications.
Magnetic Properties: Investigate the magnetic behavior of solids, including ferromagnetism, antiferromagnetism, and ferrimagnetism.
Optical Properties: Examine the interaction of light with solids, including absorption, reflection, and transmission phenomena.
With visually engaging slides, informative content, and interactive elements, our online PowerPoint presentation serves as a valuable resource for students, educators, and enthusiasts alike, facilitating a deeper understanding of the captivating world of solid-state physics. Explore the intricacies of solid-state materials and unlock the secrets behind their remarkable properties with our comprehensive presentation.
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
PPT on Alternate Wetting and Drying presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
TOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptxshubhijain836
Centrifugation is a powerful technique used in laboratories to separate components of a heterogeneous mixture based on their density. This process utilizes centrifugal force to rapidly spin samples, causing denser particles to migrate outward more quickly than lighter ones. As a result, distinct layers form within the sample tube, allowing for easy isolation and purification of target substances.
PPT on Sustainable Land Management presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
BIRDS DIVERSITY OF SOOTEA BISWANATH ASSAM.ppt.pptxgoluk9330
Ahota Beel, nestled in Sootea Biswanath Assam , is celebrated for its extraordinary diversity of bird species. This wetland sanctuary supports a myriad of avian residents and migrants alike. Visitors can admire the elegant flights of migratory species such as the Northern Pintail and Eurasian Wigeon, alongside resident birds including the Asian Openbill and Pheasant-tailed Jacana. With its tranquil scenery and varied habitats, Ahota Beel offers a perfect haven for birdwatchers to appreciate and study the vibrant birdlife that thrives in this natural refuge.
(June 12, 2024) Webinar: Development of PET theranostics targeting the molecu...Scintica Instrumentation
Targeting Hsp90 and its pathogen Orthologs with Tethered Inhibitors as a Diagnostic and Therapeutic Strategy for cancer and infectious diseases with Dr. Timothy Haystead.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
A Simultaneous dual-site technosignature search using international LOFAR stations
1. Draft version October 25, 2023
Typeset using L
A
TEX twocolumn style in AASTeX63
A Simultaneous dual-site technosignature search using international LOFAR stations
Owen A. Johnson ,1, 2, 3
Vishal Gajjar ,4, 2
Evan F. Keane ,1, 5
David J. McKenna ,1, 6
Charles Giese ,7, 1
Ben McKeon ,5, 8
Tobia D. Carozzi ,9
Cloe Alcaria ,1, 10
Aoife Brennan ,1, 5, 11
Bryan Brzycki ,2
Steve Croft ,2, 4
Jamie Drew,12
Richard Elkins,2
Peter T. Gallagher ,6
Ruth Kelly ,13
Matt Lebofsky ,2
Dave H.E. MacMahon ,2
Joseph McCauley ,1
Imke de Pater ,2
Shauna Rose Raeside ,1, 6, 14
Andrew P.V. Siemion ,2, 4
and S. Pete Worden12
1School of Physics, Trinity College Dublin, College Green, Dublin 2, Ireland
2Breakthrough Listen, University of California, Berkeley, 501 Campbell Hall 3411, Berkeley, CA, 94720, USA
3School of Physics, O’Brien Centre for Science North, University College Dublin, Belfield, Dublin 4, Ireland
4SETI Institute, 339 Bernardo Ave Suite 200 Mountain View, CA 94043, USA
5School of Natural Sciences, Ollscoil na Gaillimhe — University of Galway, University Road, H91 TK33, Galway, Ireland
6School of Cosmic Physics, Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
7Max-Planck-Institut für Radioastronomie, Bonn, Germany
8Department of Physics, University of Limerick, V94 T9PX, Limerick, Ireland
9Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
10Département de Physique, Université Paul Sabatier, Toulouse, France
11European Southern Observatory, Alonso de Córdova 3107, Vitacura, Región Metropolitana, Chile
12The Breakthrough Initiatives, NASA Research Park, Bld. 18, Moffett Field, CA, 94035, USA
13Mullard Space Science Laboratory, Department of Space and Climate Physics, UCL, Surrey RH5 6NT, United Kingdom
14School of Physical Sciences and Centre for Astrophysics & Relativity, Dublin City University, Glasnevin, D09 W6Y4, Ireland
(Received 2023 July 31; Revised 2023 August 29; Accepted 2023 September 1; Published 2023 October 24)
Submitted to AJ
ABSTRACT
The Search for Extraterrestrial Intelligence (SETI) aims to find evidence of technosignatures, which
can point towards the possible existence of technologically advanced extraterrestrial life. Radio signals
similar to those engineered on Earth may be transmitted by other civilizations, motivating technosig-
nature searches across the entire radio spectrum. In this endeavor, the low-frequency radio band
has remained largely unexplored; with prior radio searches primarily above 1 GHz. In this survey at
110 − 190 MHz, observations of 1,631,198 targets from TESS and Gaia are reported. Observations
took place simultaneously with two international stations (non-interferometric) of the Low Frequency
Array in Ireland and Sweden. We can reject the presence of any Doppler drifting narrow-band trans-
missions in the barycentric frame of reference, with equivalent isotropic radiated power of 1017
W, for
0.4 million (or 1.3 million) stellar systems at 110 (or 190) MHz. This work demonstrates the effective-
ness of using multi-site simultaneous observations for rejecting anthropogenic signals in the search for
technosignatures.
Keywords: Astrobiology (74); Exoplanets (498); Search for extraterrestrial intelligence (2127); Tech-
nosignatures (2128)
1. INTRODUCTION
In the last 50 years, evidence has steadily mounted,
that the constituents and conditions necessary for life
are common in the Universe (Wordsworth & Pierrehum-
bert 2014). Predicting specific properties of electromag-
netic emissions from extraterrestrial technologies is one
of the most challenging aspects of searching for life in the
universe. However, it also represents a high-risk, high-
reward endeavor. If an extraterrestrial civilization were
intentionally attempting to indicate its presence through
such emissions, it would be advantageous to make the
signals easily distinguishable from natural phenomena.
The evidence of such emissions is referred to as ‘tech-
nosignatures’, and the field dedicated to their detection
arXiv:2310.15704v1
[astro-ph.IM]
24
Oct
2023
2. 2 Johnson et al.
is known as the Search for Extra-terrestrial Intelligence
(SETI).
It is commonly assumed that civilizations elsewhere
in the universe may employ similar technologies to those
developed on Earth. Consequently, radio frequencies are
considered a logical domain for conducting SETI sur-
veys due to the widespread use of telecommunications
and radar. Therefore, radio astronomy has played a sig-
nificant role in the field of SETI since the 1960s (Drake
1961; Tarter et al. 1980). Numerous previous SETI sur-
veys have utilized large single dish telescopes operat-
ing at frequencies ≳ 1 GHz (Tarter 1996; Siemion et al.
2013; Enriquez et al. 2017) 1
. However, exploration of
the radio window below 1 GHz has been relatively lim-
ited. Technosignature searches commonly seek narrow-
band (approximately Hz-scale) radio emissions, either
transmitted directly or leaking from other civilizations.
Nonetheless, there is no inherent preference for any spe-
cific segment of the radio spectrum, which necessitates
surveys spanning from low frequencies (30 MHz) to high
frequencies (100 GHz; Ng et al. 2022). At 30 MHz it be-
comes very difficult to observe from the ground due to
ionospheric conditions (see Burke et al. 2019, chap. 7.8).
This study primarily focuses on low-frequency SETI in
the 110 - 190 MHz range.
1.1. Scientific Motivation
Low-frequency radio SETI presents significant chal-
lenges due to higher sky temperatures, which limit the
sensitivity of the underlying observations. The Murchi-
son Widefield Array (MWA, Tingay et al. 2013) in West-
ern Australia has been at the forefront of low-frequency
SETI research thus far (Tingay et al. 2016, 2018a,b).
However, the LOw Frequency ARray (LOFAR) presents
a compelling scientific case for conducting a SETI sur-
vey (Loeb & Zaldarriaga 2007). Aside from operating
at low frequencies in the northern sky, LOFAR offers a
large field of view, enabling the search for technosigna-
tures across thousands of stars in each observation.
Radio SETI also grapples with the challenge of han-
dling a significant amount of radio frequency interfer-
ence (RFI). Traditionally, SETI surveys have been con-
ducted using single dish radio telescopes. While these
telescopes offer operational convenience and room for
upgrades, they possess limitations in effectively distin-
guishing between sources of interference and authentic
sky-bound signals unless equipped with multibeam re-
ceivers. In contrast, the utilization of two local LOFAR
stations presents two notable advantages over conven-
tional single dish surveys. As demonstrated in studies
1 See Wright 2018 for a review
conducted by Enriquez et al. (2017) and Price et al.
(2020), single dish surveys typically employ an ’ON’
and ’OFF’ observing technique, where the target is ob-
served for five minutes (’ON’) followed by five minutes
of observing a different location (’OFF’). This cycle is
repeated three times, resulting in three ’ON’ pointings
and three ’OFF’ pointings. This approach facilitates
the identification and elimination of narrowband signals
detected in the local environment that could potentially
interfere with the search for technosignature candidates.
By employing multiple stations, the search benefits from
the unique local RFI environments at each station. This
leads to a higher rate of rejecting false positive signals
compared to the aforementioned surveys, which have
signals of interest on the order of thousands. Addition-
ally, since there are two stations involved, there is no
requirement to alternate between an ’ON’ and ’OFF’
observation regime. As a result, the entire observation
duration can be dedicated to directly observing the tar-
get, as the comparison of RFI environments would yield
the same effect. This characteristic renders SETI sur-
veys with two or more telescopes a highly valuable re-
source, particularly in today’s RFI environments.
1.2. Breakthrough Listen
The Breakthrough Listen (BL) program is conducting
one of the most comprehensive searches for evidence of
intelligent life by extending the search to a wide variety
of targets from existing ground-based observing facilities
(see Gajjar et al. 2019 for a review). All of the existing
observations within the BL program have so far been
conducted in the 1 − 27.45 GHz range (Ng et al. 2022).
In this paper we report on low frequency extension of the
BL initiative using two international LOFAR stations to
perform simultaneous dual-site observations of nearby
exoplanet candidates of interest from both the Tran-
siting Exoplanet Survey Satellite (TESS; Ricker et al.
2015) and from Gaia (Gaia Collaboration et al. 2018)
in collaboration with the BL program. This survey also
demonstrates the proof of concept of using dual-site ob-
servations for the rejection of spurious local sources of
terrestrial origin. This method thus removes the need
for separate ‘ON’ and ‘OFF’ pointings (Gajjar et al.
2021). In § 2 we describe the observational set up and
the data acquired. § 3 explains the data analysis steps
taken. We discuss the implications of this work in § 4
before concluding in § 5.
2. OBSERVATIONS
This study encompasses a total of 44 targeted point-
ings, where each pointing consists of a 15-minute scan
centered on specific targets selected from the TESS
3. Simultaneous dual-site technosignature search at 110-190 MHz 3
catalog, focusing on confirmed or candidate exoplanets
(refer to Figure 1). The entire observation campaign
spanned a duration of 11 hours, covering an area of 232
deg2
in the northern sky.
Figure 1. An Aitoff projection of the sky in Galactic coor-
dinates depicts the distribution of survey pointings, with the
Galactic disk shaded in grey. Gaia sources are omitted from
the plot due to their extremely high source density. Grey
dots represent TESS Targets of Interest (ToIs). Those tar-
gets observed during our survey are marked with red dots
at boresight with green showing the half-power beam width
(2.59◦
).
2.1. LOFAR
LOFAR, a pioneering low-frequency aperture array
telescope, spans hundreds of kilometers across Europe
and serves as a pathfinder to the Square Kilometer Array
(SKA). The array consists of a core station with outrig-
ger stations situated in the Netherlands and additional
international stations spanning multiple countries, such
as Germany, France, Sweden, Ireland, Latvia, Poland,
and the United Kingdom. Additionally, stations are cur-
rently in the process of being constructed in Italy and
Bulgaria. The LOFAR array operates using two types
of antenna, the Low Band Antenna (LBA) and the High
Band Antenna (HBA), operating at 10-90 MHz and 100-
250 MHz respectively. In this study, the HBAs at the
Irish and Swedish LOFAR station are used to carry out
observations non-interferometrically. The field-of-view
(FoV) of an international LOFAR station is rather large;
at full-width-half maximum it is 5.3, 3.4 and 2.3 deg2
at
frequencies of 120, 150 and 180 MHz, respectively (van
Haarlem et al. 2013). With such a large region where
our observations are sensitive, each pointing contains
millions of stars that can be searched for technosigna-
tures (Wlodarczyk-Sroka et al. 2020). In this survey, in
addition to the 44 TESS targets at boresight, 1,631,154
Gaia targets are covered by our observations and so are
searched for technosignatures.
2.2. Targets
A significant fraction of radio emission from Earth is
emitted in the direction of the ecliptic plane. For exam-
ple, powerful planetary radars are used to explore solar
system objects (Siemion et al. 2013) and high-powered
transmitters are used to communicate with solar system
probes (Enriquez et al. 2017). It is conceivable then that
such leakage radiation may also be emanating from other
worlds, preferentially in their planetary orbital planes.
This is why we chose TESS targets, as these are the clos-
est transiting exoplanet systems known (Borucki et al.
2008; Ricker et al. 2015). Observing these sources with
the LOFAR HBAs enables robust constraints on any as-
sociated artificial low-frequency radio emission.
2.2.1. TESS Targets
In order to determine a target list for this work, the
latest list of TESS object of interests (TOIs) was re-
trieved (NASA Exoplanet Science Institute 2020) and a
shortlist of targets were obtained rejecting possible false
positives. Since the sensitivity of the HBA array is best
±30◦
of zenith, the required overlap for both LOFAR
international stations spans the declination range +27◦
to +83◦
. Further practical considerations were also ac-
counted for, i.e. to stay as far from bright sources like
the Sun as possible at both sites, and to balance sensi-
tivity at both sites (Johnson 2023)2
. We report obser-
vations towards 44 unique targets from the TESS cata-
logue in this study, where each target was observed for
15 minutes. Figure 1 shows the distribution of these
targets observed in comparison to the pool of all TESS
TOIs.
2.2.2. Gaia Sources
The beam of a LOFAR station has an expansive cov-
erage enabling observation of a substantial number of
stars in the field-of-view. The significance of these in-
field stars has been highlighted by Wlodarczyk-Sroka
et al. (2020). Consequently, during our observations
targeting 44 sources from the TESS catalogue, we en-
countered a significant number of in-field stars within
our field-of-view as shown in Figure 2.
2 These selection criteria were applied using a custom developed
dual-site observation planning software.
4. 4 Johnson et al.
Figure 2. This figure illustrates one of the boresight point-
ings directed at a TESS object (highlighted in green), with
the LOFAR beam’s Full-Width Half-Maximum (FWHM)
shown in pink. The background image is from the Sloan
Digital Sky Survey (Albareti et al. 2017, SDSS;).
To determine the list of targets within this field-of-
view, we utilized the Gaia catalogue. Some previous
major SETI surveys focused their searches towards
Sun-like stars (Tarter 1996). However, since our under-
standing of the origin of life is limited, it makes sense to
allow for the possibility of life arising on a planet that
is neither Earth-like, nor around stars that are Sun-like.
Similarly, we should consider planets not necessarily
located in the habitable zone. This is typically charac-
terized as the orbital range wherein liquid water could
exist (Kasting et al. 1993), as inferred from planetary
equilibrium temperatures often ignoring the unknown
albedo of the exoplanets. Any sensitive radio SETI
survey seeking to maximize the chance of detecting
weak radio signals should, insofar as possible, expand
its search to encompass nearby stars of a broad range
of spectral types and with exoplanets of all sizes and
distances from their parent star. Thus, we conducted
calculations to determine the number of Gaia stars with
a mean distance of 1215 pc, with an accuracy in their
distances of at least 20%.
This study used Gaia’s third data release (GDR3;
Gaia Collaboration et al. 2023; Ginsburg et al. 2019).
When analyzing GDR3 two filters were applied to the
in beam target values survey volume and sensitivity ac-
curacy. Firstly a constraint on the RA and DEC errors
were implemented. If a Gaia source was found to be in
the beam but had a error magnitude greater than the
FWHM it was removed from the source pool. Equa-
tion (1) states the first condition of filtering.
θsep +
p
∆RA2
+ ∆DEC2
< 1.295◦
(1)
As the sensitivity of the survey is calculated based on
a source’s distance a second filter is implemented to re-
move sources that have large errors. By taking the dif-
ference (∆σG) in the upper and lower confidence levels
of GSP-Photometry3
to obtain a percentage error on dis-
tance. All sources with a dMG
error of 20% or greater
are filtered out of the source list. Equation (2) states
the second condition of filtering:
∆σG
dMG
< 20% (2)
A total of 1, 631, 154 stars from this list, making it one of
the largest samples of stars ever surveyed for SETI pur-
poses. Figure 3 shows a Hertzsprung-Russell diagram
for the targets.
2.3. Simultaneous observations
Typically, international LOFAR stations operate as
standalone telescopes 2 − 3 days per week, i.e. they do
not operate as part of the International LOFAR Tele-
scope’s Europe-wide array. This project was undertaken
during this standalone time. For this purpose the inter-
national LOFAR in Stand-Alone mode (iLiSA) package4
is used to control both telescopes simultaneously. iLiSA
provides a high-level operational control of multiple LO-
FAR stations, including scheduling, processing pipeline
dispatching and metadata aggregation (see Figure 5).
For the observations in this study, an operator-produced
list of targets that were close5
to the local meridian
was fed into iLiSA at each epoch. Towards each tar-
get, one beam per station was formed using iLiSA, and
each beam was formed with 412 HBA sub-bands (corre-
sponding to a bandwidth of 80.46875 MHz). The scan
time on each target was 15 min, and the whole schedul-
ing block was a few hours per epoch.
In this study, the only iLiSA pipeline used was the
raw data recorder, which simply receives UDP packets
of beam-formed data and writes them to disk, separately
at each site. The data consist of coarse-channelised com-
plex voltages. The initial data stream is two polariza-
tion’s from each antenna. With real Nyquist-sampling
with a 200-MHz clock, with a coarse channelisation fac-
tor of 512 taking place, only 488 (244) of these be-
ing recordable when the data are written as 8-bit (16-
bit) complex numbers. Further processing of these data
3 SQL Keys: distance gspphot, distance gspphot upper (dMG
)
and distance gspphot lower
4 https://github.com/2baOrNot2ba/iLiSA/releases/tag/v6.1
5 In practice as Birr and Onsala are separated by ∼ 20 deg of lon-
gitude, the optimum scheduling is to observe ∼ 40 min−Tobs/2
‘late’ at Onsala and 40 min+Tobs/2 ‘early’ at Birr.
5. Simultaneous dual-site technosignature search at 110-190 MHz 5
Figure 3. A Hertzsprung-Russell diagram of the 1,631,198
Gaia targets searched for technosignatures in this survey
with a mean distance of 1270 pc. The relative distribu-
tion with respect to spectral type is: O < 0.01%, B—0.4%,
A—6.94%, F—11.01%, G—31.56%, K—47.84%, M—2.12%.
This is as opposed to the general Gaia catalogue which is:
O, B < 0.0001%, A—1.5%, F—18.9%, G—44.4%, K—34.5%,
M—0.6%.
0.0 0.2 0.4 0.6 0.8 1.0 1.2
Off-Beam Angle, θ [deg◦ ]
50%
60%
70%
80%
90%
100%
Beam
Sensitivity
105
106
Number
of
Gaia
Targets
FWHM
Figure 4. The LOFAR HBA beam’s sensitivity at 150 MHz
changes in relation to the off-axis bore-sight angle (θ). Fur-
thermore, a plot of the number of filtered Gaia targets within
the beam pointing as a function of θ is presented. The × rep-
resents the value for the Full Width Half Max of the beam.
Table 1. Specifications for the data input to our
processing pipeline after pre-processing and prepar-
ing the raw data with udpPacketManager (McKenna
et al. 2023a).
Data Attribute Value
Frequency Start (fstart) 109.9609375 MHz
Frequency End (fend) 190.0390625 MHz
Frequency Resolution 2.980232239 Hz
Channel Number 27000832
Obs. Length (tobs) 15 mins
Temporal Resolution 0.67108864 s
Maximum Drift Rate Search ±4 Hz s−1
S/Nmin threshold 10
is necessary and we use udpPacketManager (McKenna
et al. 2023a) to ultimately create total intensity sigproc
(Lorimer 2011) formatted filterbank files at the time and
frequency resolution appropriate for our Doppler-drift
search, shown in Table 1.
3. ANALYSIS
The most common transmissions sought in SETI
searches are narrow-band (∼Hz) radio signals. Ubiq-
uitous in early terrestrial communication systems, such
signals can be produced with relatively low energy and
traverse the interstellar medium easily. They can be
readily distinguished from natural astrophysical sources.
6. 6 Johnson et al.
Figure 5. iLiSA block diagram, showing how an operator-defined schedule is ingested and is executed in a timely fashion.
Data then begins to flow and ends up being ingested by processing pipelines together with associated metadata.
These signals could either be transmitted intentionally
or arise as leakage from extra-solar technologies. The
apparent frequency of a distant narrow-band transmit-
ter is expected to exhibit Doppler drift due to the rela-
tive motion between the transmitter and receiver. The
Breakthrough Listen group has developed an efficient
narrow-band search software package which includes a
search for such drifting signals, named turboSETI (En-
riquez et al. 2017) which we use for the analysis of our
LOFAR survey data. However, before we can compare
narrowband signal hits detected using this tool, it was
necessary to compare them in the Barycentric reference
frame.
3.1. Barycentric correction
The movement of the Earth around its axis and the
Sun introduces a Doppler effect that causes radio signals’
frequency and arrival time to shift, as
fobs = fem (1 − vrel) . (3)
Here, fobs is the observed frequency, fem is the emitted
frequency (or barycentric frequency), and vrel is the ve-
locity of the source relative to the observer, normalized
by the speed of light. The Doppler effect only depends
on the velocity of the source relative to the observer, and
for a source moving towards the observer, we can con-
sider −vrel, while for a source moving away from the ob-
server, we consider +vrel. The relative velocity between
the observer and the source will differ for different ob-
serving epochs, the location of the source in the sky, and
the geographical location of the telescope. For instance,
the target TIC 27677846 was observed on UT 2021 July
15, from both the LOFAR stations simultaneously. The
expected relative velocity (vrel) towards the source was
−7.669 × 10−5
and −7.496 × 10−5
, causing a relative
shift (fem − fobs) of +11.504 kHz and +11.246 kHz for
a hypothetical ETI signal transmitted at a constant fre-
quency of 150 MHz observed at the Sweden and Ireland
stations, respectively. These are significant shifts that
are distinct at the two stations, and they need to be cor-
rected to compare the same signal observed at the two
stations.
Typically, barycentric corrections are introduced by
adjusting the local oscillator during observations. How-
ever, in our study, we record beamformed baseband
voltages during observations and produce three different
data products with varying temporal and spectral res-
olutions during post-processing (Lebofsky et al. 2019).
We are interested in searching for a wide variety of sig-
nals, including narrowband signals, broadband transient
signals, and wide-band pulsating signals. Introducing lo-
cal oscillator shifts during observations can impact our
other signal searches. Therefore, we correct for barycen-
tric drift after the channelization and detection of the
baseband voltages for narrowband signal searches us-
ing software which we have developed6
. Details of this
correction and code (Gajjar 2023) are fully discussed
in Appendix A. For comparison both topocentric and
barycentric data are analysed for a small sub-set of the
targets and the results are shown in Table 2.
3.2. Searching for Narrowband Signals
Using turboSETI with the parameters outlined in
Table 1, a Doppler drift search was carried out on the
observed candidates listed in Table 3 and 4 at both
stations. This resulted in the list of ‘hits’ collected in
Tables 3 and 4, where hits are defined as a narrow-band
signal detected above the given threshold, S/N = 10.
The distribution of narrow-band signals detected at
both stations is shown in Figure 6. A large percentage
of hits are seen at both sites in the 120 - 140 MHz range.
This falls within the range of expected RFI leakage seen
6 https://github.com/gajjarv/BaryCentricCorrection
7. Simultaneous dual-site technosignature search at 110-190 MHz 7
Table 2. Comparison of the number narrow-band signals detected for a sub-set of TESS objects in both the
topocentric and barycentric reference frame. turboSETI searches were completed using identical parameters in
each reference frame. We did find a small number of mutual hits while it was found that Barycentrically correcting
the data prior to searching filtered out all prior mutual hits of interest.
TIC ID LOFAR-SE Hits I-LOFAR Hits Mutual Hits LOFAR-SE Hits I-LOFAR Hits Mutual Hits
Topocentric Results Barycentrically Corrected Results
121966220 387 178 18 376 171 0
249862365 340 193 22 330 196 0
250724252 276 190 21 265 262 0
27677846 313 159 20 294 151 0
470315428 384 175 17 356 224 0
from neighboring airports7
.
Using a drift-rate search of ±4 Hz/s for this study
covers a fraction of the possible drift rates of trans-
mitters from exotic objects that can be detected as
outlined by Sheikh et al. (2019). Li et al. (2022) shows
that 4 Hs/s is comprehensive in relative to the expected
distribution of exoplanet drift rates. The omission of
a search in this parameter space is due to its compu-
tationally intense nature of searching for narrow-band
signals across a sizeable drift-rate range. However, in
doing this, the parameter space searched for ETI signal
has been drastically reduced. Continual development
of search algorithms like turboSETI is progressing to
make larger drift-rates searches a more computationally
feasible.
Upon first inspection of Figure 6 it appears that the
results at both stations are somewhat similar. However,
upon performing a Kolmogorov-Smirnov (KS) test for
each set of results for drift-rate, SN and frequency of
detected hits the highest p-value returned was on the
order of 10−11
indicating that the RFI environments at
each of the stations are significantly different.
3.3. Dual-site coincidence rejection
In the case of this study, a singular beam observes
a single target for 15 minutes at both stations and ob-
servations are converted to barycentric reference frame.
Narrow-band searches are then performed at both sites,
and the results of both searches are compared. In Fig-
ure 8 two common detection cases are shown and how
the use of dual site observation aids in the nature of each
signals origin.
7 Shannon & Goteborg Landvetter
Case A: In this case a hit has been detected at the
Irish station but is absent from the same frequency at
the Swedish station. Thus the signal is rejected as a
extraterrestrial emitter and deemed as RFI local to the
Irish station.
Case B: Similar to case A but this time the converse
is seen, a hit has been detected at Swedish station and
not at a the frequency at the Irish station.
In our analysis, a signal is classified as a mutual ex-
traterrestrial hit only if two conditions are met: a) the
signals are within a frequency range of ±4 Hz of each
other in the barycentric reference frame, and b) their
drift rates are within ±0.2 Hz/s of each other after
barycentric drift corrections. In Figure 9, an intrigu-
ing candidate is depicted. In the topocentric frame, we
detected a narrowband signal at 160 MHz that was si-
multaneously present at both stations. However, when
converting to the barycentric reference frame (as illus-
trated in Figure 9), the signal appears to be seen at
different frequencies with opposite signs due to the dif-
ferent line-of-sight velocities towards the target. As a
result, this narrowband signal is rejected as a genuine
sky-bound signal.
3.4. Search Results
Figure 7 depicts the observed drift rates as a func-
tion of frequency. As shown in Figure 6, a substantial
number of hits are observed at 125 MHz and 138 MHz,
suggesting the presence of potential aircraft commu-
nications within these frequency bands. Notably, at
I-LOFAR, a significant number of hits are also detected
at 167 MHz, which is suspected to be related to aircraft
communication. Additionally, a pronounced spike in
RFI at 164 MHz is observed at the Swedish station
(LOFAR-SE), likely associated with marine communi-
8. 8 Johnson et al.
2%
4%
6%
8%
110
120
130
140
150
160
170
180
190
Frequency
[MHz]
nhits = 10908
Ireland
2% 4% 6% 8%
nhits = 11579
Sweden
10%
30%
50%
70%
−4
−3
−2
−1
0
1
2
3
4
Drfit
Rate
[Hz/s]
10% 30% 50% 70%
4%
8%
12%
16%
20%
0
25
50
75
100
125
150
175
200
S/N
4% 8% 12% 16% 20%
Figure 6. Comparison of drifting signals or ‘hits’ detected
at both stations seen across the HBA frequency band. Each
bin within the data set represents a 1 MHz frequency range
and is accompanied by a corresponding percentage indicating
its proportion to the overall data set.
110 120 130 140 150 160 170 180 190
Frequency [MHz]
−4
−3
−2
−1
0
1
2
3
4
Drift
Rate
[Hz/s]
Ireland
Sweden
Figure 7. A scatter plot of the drift rate values against
detected frequency. The Irish station is shown in pink and
the Swedish station is shown in blue.
cations due to the proximity of LOFAR-SE to the coast.
Implementing barycentric corrections and coincidence
rejections, no signals of interest were identified among
the observed candidates. Comprehensive information
regarding the targets and their corresponding hits for
both TESS and Gaia can be found in the supplemen-
tary databases presented in the Tables 3 and 4.
4. DISCUSSION
4.1. Survey Sensitivity
The required power for a certain extra terrestrial in-
telligent (ETI) transmitter to be detected depends on
its directionality and other signal characteristics. We
can measure the transmitter power of an ETI beacon in
terms of the effective isotropic radiated power (EIRP;
Enriquez et al. 2017) as,
EIRP = σ × 4πd2
⋆
SEFD
δνt
s
δν
nptobs
W (4)
Here, σ is the required S/N, δν is the bandwidth of the
received signal, δνt is the transmitted bandwidth, tobs
is the observing integration time, SEFD is the System
Equivalent Flux Density, np is the number of polariza-
tions, and d⋆ is the distance between the transmitter and
the receiver, i.e., the distance to the star. We considered
δνt to be 1 Hz. For the narrowband signals we consider
in our Doppler searches, we assume δν is matched to our
spectral resolution and further assume a temporal duty
cycle of 100%.
9. Simultaneous dual-site technosignature search at 110-190 MHz 9
Figure 8. Dynamic spectra (waterfall plots) of detected narrow-band signal centered on the detected frequency of detection,
showing the two most common cases of coincidence rejection. Case A (left) shows a narrowband signal with a non-zero drift
rate detected at I-LOFAR and not LOFAR-SE. Case B (Right) shows the opposite where a non-zero drift rate signal is not
detected by I-LOFAR but is detected by LOFAR-SE. For a signal to be considered a detection of interest both sites would have
to exhibit non-zero drift rate signal at the same frequency simultaneously.
Table 3. TESS candidates used as bore sight pointings for survey. These targets were obtained from the NASA Exoplanet
Archive (NEA) Targets of Interest database. Selection criteria was based on what targets were visible at both stations.
TIC ID MBJD Start RA DEC Distance LOFAR-SE Hits I-LOFAR Hits Mutual Hits
J2000 Hours J2000 Degrees pc
27677846 59410.3856 4.424676 46.365902 78.71 ± 0.330 294 151 0
51024887 59410.3189 2.810346 62.189260 41.53 ± 0.158 265 181 0
81831095 59410.3300 3.187109 61.762385 399.40 ± 5.300 277 196 0
121966220 59410.3967 5.053188 41.785784 472.70 ± 9.135 376 171 0
142090065 59402.4266 5.271567 79.737727 182.91 ± 1.291 290 282 0
191146556 59410.4078 0.553625 46.340305 282.83 ± 3.011 378 266 0
249862365 59410.3078 2.541534 52.704091 184.69 ± 1.290 330 197 0
250724252 59410.2967 2.233683 53.121508 574.87 ± · · · 265 262 0
266500992 59410.3634 4.078149 52.256992 165.31 ± 0.987 276 164 0
288132261 59403.5613 13.965621 79.583322 154.94 ± 0.521 328 310 0
First 10 entries of the table, full table available with paper’s supplementary material.
Note—The above table contains relevant parameters to each observed target and the resultant hits attained from the narrow-
band search at respective stations. A * denotes a confirmed exoplanet in the NEA. The distance is inferred from Bailer-Jones
et al. (2018) which makes use of GDR2 parallax values.
The SEFD of the international HBA stations used in
this survey is on average ∼ 900 Jy for most of the band,
rising to ∼ 1.2 kJy at the band edges (van Haarlem
et al. 2013). For reference, the SEFD of the GBT at
the 1.4 GHz is around 10 Jy. This difference in sensi-
tivity is because sky temperature scales as ν−2.6
mean-
ing it can be hundreds of times higher in the LOFAR
band. However, the average values are of little use as
there is also a large degree of variation in the sky tem-
perature across the sky. For this reason, we perform a
separate calculation for every target to determine the
relevant luminosity limit in each case. For example, the
sensitivity to each off-boresight target is determined by
its proximity to the pointing coordinates. Figure 4 de-
picts both the impact on sensitivity and the number of
background stars within a given LOFAR beam. Figure
10. 10 Johnson et al.
Figure 9. The top two plots represent narrowband signals detected at both stations in the topocentric frame of reference. The
bottom two plots show the same detected narrowband signals detected at both stations but corrected to the barycentric frame
of reference. This is illustrated by the newly added drift to signals present in the post correction.
2 shows an example pointing from the survey and also
well illustrates the vast volume of targets that appear in
a LOFAR beam (pink).
Figure 10 presents the luminosity limits for the cumu-
lative targets of this survey within the frequency range of
110−190 MHz. In this figure, the limiting luminosity is
compared to notable values of Equivalent Isotropic Ra-
diated Power (EIRP) for various scenarios. These sce-
narios include a Kardashev I type advanced civilization
transmitting at a power level of 1017
W, an advanced civ-
ilization producing planetary radar-level transmissions
with a transmitting power of 1013
W, and a cumulative
aircraft radar-type system transmitted across a large
solid angle with a power of 1010
W (Siemion et al. 2013).
The Figure demonstrates that due to the varying system
temperature (Tsys) across the frequency band, our ob-
servations were sensitive to detecting a range of Karda-
shev I type targets. Specifically, we were able to detect
approximately 25% of the targets at the lower end of the
frequency band, increasing to nearly 80% of the targets
at the higher end of the band.
4.2. Starlink Interference
A recent study by Di Vruno et al. (2023) has shown
that unintended electromagnetic radiation (UEMR)
from the Starlink satellite constellation produced broad-
band interference ranging from 0.1 to 10 Jy and narrow-
band interference ranging from 10 to 500 Jy. UEMR
was detected at frequencies at 110 to 188 MHz, which is
the bandwidth of the HBA used in this study. UEMR
has many potential consequences for low frequency ra-
dio observations. Analysis of turboSETI hit detection’s
within 1 MHz the UEMR narrowband emission frequen-
cies (125, 135, 143, 150, 175 MHz; Di Vruno et al. 2023)
show that 17.8% of total detected hits are within this
region. This region occupies 18.5% of this study’s band-
width. This result is expected, as UEMR affects a num-
ber of different types of radio searches, it does not affect
11. Simultaneous dual-site technosignature search at 110-190 MHz 11
Table 4. Gaia candidates found within 1.295◦
of TESS boresight pointing. The Gaia target pool makes use of GDR3, filtering was applied to
the target pool based on the error of parallax. Gaia targets that exhibit a distance error of 20% or more are cut from the data set as their EIRP
sensitivity.
Gaia ID RA DEC Distance Teff Pointing Separation TIC ID LOFAR-SE Hits I-LOFAR Hits Mutual Hits
J2000 Degrees J2000 Degrees pc K deg
540394404387737000 0.003867 77.7984 850.636 4954.0 1.129 407394748 257 181 0
540420788369495000 0.008171 77.9843 836.863 5387.3 1.093 407394748 257 181 0
540290637978301000 0.011819 77.5007 563.690 4686.4 1.013 407394748 257 181 0
540431753423271000 0.017921 78.2404 1293.320 5365.0 1.295 407394748 257 181 0
540422957330267000 0.018887 78.0603 722.054 5415.4 0.958 407394748 257 181 0
564460068219877000 0.018908 78.4901 1415.490 5276.0 1.189 407394748 257 181 0
540394400090438000 0.020346 77.7933 861.226 5896.3 1.118 407394748 257 181 0
540387257562774000 0.021907 77.6559 818.213 4952.0 0.947 407394748 257 181 0
564451272126871000 0.022257 78.3080 854.196 4731.2 1.089 407394748 257 181 0
540291153374376000 0.022550 77.5313 1105.790 4892.0 0.985 407394748 257 181 0
First 10 entries of the table, full table available with paper’s supplementary material.
Note—The above table contains the details of each Gaia target found in a specific TESS pointing and associated separation from the boar sight of the LOFAR beam.
0.00
0.25
0.50
0.75
1.00
110 MHz
25.5 %
120 MHz
34.5 %
130 MHz
43.9 %
0.00
0.25
0.50
0.75
1.00
140 MHz
52.9 %
150 MHz
60.6 %
160 MHz
67.0 %
10 12 14 16 18 20
EIRP [log(W)]
0.00
0.25
0.50
0.75
1.00
170 MHz
72.0 %
10 12 14 16 18 20
EIRP [log(W)]
180 MHz
75.9 %
10 12 14 16 18
EIRP [log(W)]
190 MHz
79.0 %
Figure 10. Cumulative histogram of EIRP limits of this survey across the HBA band. Reference luminosities for three
civilization levels emitting 1017
, 1013
or 1010
W are shown in blue, red and green respectively. The percentage of targets where
the station is sensitive to the transmission of 1017
W is shown, as a function of frequency across the band. At lower frequencies
sensitivity to 1017
emitters drops off as the Tsys rises. The T̄sys varies from 1260 K down to 322 K as frequency is increased
across the band. Detailed calculations are presented in Appendix B.
12. 12 Johnson et al.
narrowband searches of this nature. This is due to two
factors. Firstly satellites in Low Earth Orbit (LEO) to
Geostationary orbit (GEO) usually have velocities that
are too high for them to be detected with the temporal
resolution of our data, and they are at drift rate values
outside the parameters of this search (>4 Hz/s). Sec-
ondly, the satellites are in the near field of each station’s
beam and due to their relative distance to the observer
compared to the bore sight target a satellite less likely
to appear in both beams simultaneously. It is concluded
that the Starlink constellation does not add to the num-
ber of narrowband hits detected in this study.
4.3. Figure of Merit
To compare SETI surveys, Enriquez et al. (2017) in-
troduced a figure of merit known as the Continuous
Waveform Transmitter Rate (CWTFM),
CWTFM = ζAO
EIRP
Nstarsνrel
(5)
Where Nstars is the number of stars in each pointing
for a given survey, νrel is the fractional bandwidth of the
survey, ∆νtot/νmid where νmid is the central frequency
of the survey. ζAO is the normalization factor such that
CWTFM = 1 and the EIRP is equal to the Arecibo radio
telescope’s S-band planetary radar, if it were transmit-
ted across a whole hemisphere, (∼ 1013
W Siemion et al.
2013). In Figure 11, we compare our results to those
from some other SETI surveys. As this survey contin-
ues, the transmitter rate will decrease with the volume
of stars observed (Nstars), as outlined by Equation (6).
Transmitter Rate = log
1
Nstars · νrel
(6)
As dictated by Equation (4) to be sensitive to lower
powered ETI transmitters, the observation sensitivity
needs to be greater. This can be done by employing
further LOFAR stations for n-site simultaneous obser-
vations through coherent summation.
4.4. 110 - 190 MHz Technosignature Parameter Space
The number of intelligent civilizations is quantified us-
ing Equation (7), coined by Drake (1961).
N = R∗fpNeflfifcL (7)
In this expression N is the number of communicative
civilizations in the Milky Way galaxy, R∗ is the rate of
star formation per year in the galaxy, fp is the fraction
of stars that have planets around them, ne is the average
number of planets that can potentially support life per
star that has planets, fl is the fraction of potentially
life-supporting planets that actually develop life, fi is
the fraction of planets with life that go on to develop
intelligent life and fc is the fraction of civilizations that
develop a technology that releases detectable signs of
their existence into space.
In Gajjar et al. (2022) a modified variation of the
Drake equation (Equation. (8); Shklovskii Sagan
1966) is used to constrain the fraction of narrowband
emitting civilizations (fn
c ).
N = RIPfn
c L (8)
Here RIP is defined as the emergence rate (yr−1
) of in-
telligent life in the Milky Way. Figure 12 shows the con-
straint that this survey places on fn
c when using a Pois-
son sided upper limit at 95% confidence which in this
case is 2.995 as per Gehrels (1986). This provides the
most strigent constraint of fn
c in this frequency range.
4.5. Future work using LOFAR 2.0
LOFAR is soon to undergo a staged series of upgrades
across all stations in the array. These upgrades at indi-
vidual stations across Europe will involve the installa-
tion of a new Receiver Control Unit (RCU) as described
in ASTRON (2023). These RCUs will enable the simul-
taneous use of both the LBA and HBA in the frequency
range of 15 - 240 MHz. This enhancement will allow for
a SETI survey across a broader low-frequency band.
Specifically, at 30 MHz, the FWHM will cover an
area of 19.39 deg2
, decreasing to 1.73 deg2
at 190 MHz.
This will enable follow-up LOFAR surveys to encom-
pass a larger volume of stars and a broader frequency
domain.
5. CONCLUSION
This paper presents a SETI search in a mostly un-
explored parameter space as seen with other SETI sur-
veys (Gajjar et al. 2021; Price et al. 2018) by simulta-
neously observing TESS and Gaia targets of interest in
the 110 − 190 MHz radio window. It also demonstrates
dual-site coincidence rejection showing that it provides a
new method to discriminate candidate extra-terrestrial
signals from terrestrial radio frequency interference. We
propose this method as a promising means of follow-up
for confirmation of any candidates interest arising in this
type of study or others in this frequency range. Each
target within our fields was then searched for narrow-
band signals at each station using our most up to date
search techniques (Enriquez et al. 2017). The benefit
of barycentric correction for eliminating false positives
is also demonstrated. Finally the first stringent con-
straints on the fraction of transmitting civilizations at
13. Simultaneous dual-site technosignature search at 110-190 MHz 13
10 12 14 16 18 20 22 24
EIRP [log(Watts)]
−12
−10
−8
−6
−4
−2
0
2
4
Transmitter
Rate
h
log
1
N
stars
·v
rel
i
Price (2019 - Parkes)
Price (2019 - GBT)
Enriquez (2017)
Gray Mooley (2017)
Harp (2016) a,b
Harp (2016) c
Harp (2016) d
Harp (2016) All*
Siemion (2013)
Phoenix
Phoenix All*
Horowitz Sagan (1993)
Valdes (1986)
Tarter (1980)
Verschuur (1973)
Gajjar (2021 - GBT)
Gajjar (2021 - Parkes)
Suresh (2023)
Dual-site LOFAR HBA
Figure 11. Comaprison of our study (highlighted in red) to prior surveys. The plot presents the transmitter rate versus
Effective Isotropic Radiated Power (EIRP), with the grey line indicating the transmitter rate as a function of EIRP. A solid
vertical grey line illustrates the energy surplus of a Kardashev Type-I civilization. Additionally, a dotted-dashed grey line
depicts the EIRP of the Arecibo planetary radar. The gray thick line shows the slope of the transmitter-rate as a function of
their EIRP power. Distance used for EIRP calculation is ¯
d + dσ = 7009 ly.
1013
1014
1015
1016
1017
1018
1019
Narrowband EIRP [W/Hz]
10−6
10−5
10−4
10−3
10−2
10−1
100
Narrowband
Producing
Fraction
(f
n
c
)
Figure 12. The fraction of stars that produce narrow-band
emission (fn
c ) against the transmitter power of the total tar-
get pool. The hashed region (red) shows the constraints this
survey places on a value of fn
c at 110 - 190 MHz.
this frequency range have been shown further contrain-
ing the parameter space the Drake equation presents.
As the LOFAR SETI observation campaign continues
and more high resolution frequency data is collected,
a machine learning search method comparable to Ma
et al. (2023) can be trained and implemented to seek
out signals of interest. Multiple LOFAR stations, or
indeed sub-arrays of any other wide-footprint radio ar-
ray allows the option for a coincidence rejection method
over the ‘ON’ and ‘OFF’ beam pointings used previ-
ously. For future low-frequency SETI surveys, the use
of further international stations and a prolonged obser-
vation campaign will place even further constraints on
an ETI residing in this parameter space. The addition
of one or more LOFAR stations would allow for the use
of localising a signal of interest in the u-v plane which
would be useful for follow up observations. This would
be done post-facto through correlation of saved voltages
for any candidates of interest.
ACKNOWLEDGMENTS
Breakthrough Listen is managed by the Breakthrough
Initiatives, sponsored by the Breakthrough Prize Foun-
dation. D.McK and AB are supported by Government
of Ireland Studentships from the Irish Research Coun-
cil (IRC). I-LOFAR has received funding from Science
Foundation Ireland (SFI), the Department of Further
and Higher Education, Research, Innovation and Science
(DFHERIS) of the Government of Ireland. We acknowl-
edge support from Onsala Space Observatory for the
14. 14 Johnson et al.
provisioning of its facilities and observational support.
The Onsala Space Observatory national research infras-
tructure is funded through Swedish Research Council
grant No 2017-00648. This research has made use of
the NASA Exoplanet Archive, which is operated by the
California Institute of Technology, under contract with
the National Aeronautics and Space Administration un-
der the Exoplanet Exploration Program. This work
also presents results from the European Space Agency
(ESA) space mission Gaia. Gaia data are being pro-
cessed by the Gaia Data Processing and Analysis Con-
sortium (DPAC). Funding for the DPAC is provided by
national institutions, in particular the institutions par-
ticipating in the Gaia MultiLateral Agreement (MLA).
This work has relied on NASA’s Astrophysics Data Sys-
tem (ADS) Bibliographic Services and the ArXiv. This
work has made use of the VizieR catalogue access tool,
CDS, Strasbourg, France. The original description of
the VizieR service was published in AAS 143, 23. We
also acknowledge the support and comments from Laura
C. Cotter and the Berkeley SETI REU Program, classes
of 2021 and 2022. We also thank the anonymous review-
ers for their careful reading of our manuscript and their
many insightful comments and suggestions.
Facilities: LOFAR Stations IE613 and SE607
Software: sigproc (Lorimer 2011), udpPacketMan-
ager (McKenna et al. 2023a), turboSETI (Enriquez et al.
2017), blimpy (Price et al. 2019), astropy (Astropy Col-
laboration et al. 2022), astroquery (Ginsburg et al. 2019),
pandas (pandas development team 2020)
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16. 16 Johnson et al.
APPENDIX
A. POST-DETECTION BARYCENTRIC CORRECTION
We have developed a novel barycentric correction code specifically designed for high-spectral resolution sigproc
filterbank products for technosignature searches (Gajjar 2023). The code uses the TEMPO routine to calculate
relative velocity towards the observing targets at both locations, thus allowing for precise correction of the barycentric
drift.
-24 -12 0 12 24
Frequency (Hz) - 1419.881942 MHz
0
50
100
150
200
250
Time
(seconds)
+vrel
-23 -11 0 11 23
Frequency (Hz) - 1419.878560 MHz
0
50
100
150
200
250
+vrel
-26 -13 0 13 26
Frequency (Hz) - 1420.096949 MHz
0
50
100
150
200
250
vrel
-24 -12 0 12 24
Frequency (Hz) - 1420.092847 MHz
0
50
100
150
200
250
vrel
Figure A.1. Doppler drift of a narrowband signal in the topocentric observing frame at four different observing epochs.
Simulated waterfalls with narrowband signals observed from the Irish LOFAR station towards the direction of TIC 27677846
are shown for different times of the year in blue. The expected sign and direction of change of the relative velocity are labeled
at the top of each plot. It is assumed that a hypothetical narrowband ETI signal is transmitted at a constant frequency of
1420 MHz (with zero drift rate). As shown, the same signal is observed at different frequencies and drift rates depending on
the sign and direction of change of the relative velocity at different epochs of observations. For instance, in the first panel, the
relative velocity is positive and increases with observing time. Therefore, the observing frequency has been shifted to a lower
frequency (as described by Equation 3), and it continues to shift to even lower frequencies with time.
The Doppler shift caused by the relative motion between the transmitter and receiver will change over time as it
is observed. Over a longer time frame, these shifts will exhibit a sinusoidal curve with a sidereal year period. Over
a shorter time frame, the same pattern (superimposed on the yearly pattern) will be visible, but with a sidereal day
period. Consequently, the relative velocity will change during the observation period, thereby altering the observed
frequency of the received narrowband signal. This leads to a drift in the narrowband signal observed by the observer.
Figure A.1 displays examples of observed drifts at four different epochs for the same narrowband signal source observed
from the same location. It is evident that if the relative velocity is positive and increasing with time (leftmost plot
in Figure A.1), the signal, which is stationary in the barycentric frame, will drift towards lower frequencies as time
progresses in the topocentric frame, as per Equation 3.
A.1. Algorithm outline
Figure A.2 shows an example of how data is arranged in a filterbank file. For our case, we will assume that in a given
filterbank file, frequency channels are in descending order with the first channel (f1) having the highest frequency for
each time sample. The goal of our tool is to shift every frequency channel from the observing frame to the actual
emitted frequency frame after correcting for the barycentric relative velocity to remove any additional narrowband
signal drift introduce by it. We aim to keep the first channel frequency of all the time samples the same in the
barycentric frame also, thus relative shifts between spectras are needed to apply for each time sample corresponding
to the inferred relative velocities. Our tool measures relative velocity at each time sample towards a given direction
in the sky from a given telescope at the time of observations. Let’s assume an observing scenario where vrel 0.
Following Equation 3, we can state that the emitted frequency (or barycentric frequency) will be higher than the
observed frequency. That means that observations stored in the first topocentric frequency channel correspond to
higher barycentric frequency. Thus, this spectra needs to be shifted to higher frequency. If the relative velocity
increases with time, the consecutive time sample’s first channel barycentric frequency will be slightly higher than the
17. Simultaneous dual-site technosignature search at 110-190 MHz 17
previous sample’s first channel emitted frequency. Our tool thus shifts the spectra of each time sample towards higher
frequency such that the first channel’s emitted frequency matches across all time samples. Due to this shifts, we either
replace empty channels at the edge of the spectra with zeros in case of squeeze or drop extra channels in case of
expansion.
As given in Equation 3, the Doppler shifts are frequency-dependent, impacting higher frequencies more than lower
frequencies. In other words, for spectra where frequencies are ordered from higher to lower frequency, the first channel
will be shifted more compared to the last frequency channel. To compensate for this, we either expand or squeeze
spectra as shown in Figure A.3. Figure A.4 outlines the logical flow of the code for a case of an input filterbank file
with a descending order of frequency. By comparing Figure A.1 and the code outline in Figure A.4, we can consider
one of the cases where the relative velocity is negative and increasing in absolute value with time. In this case, we need
to shift consecutive spectra to lower and lower frequencies to match up their first frequency channel. Furthermore, for
any negative relative velocity (either increasing or decreasing with time), we need to squeeze the individual spectra as
shown in Figure A.3. Similarly, the same can be consider for the case of positive relative velocity. The code for this
algorithm is publicly available here8
.
Frequency
Time
f1 f2 f3 f4
T2
f1 f2 f3 f4
T1
Figure A.2. A typical filterbank file stores data in a time and frequency matrix format. Each row represents a sample, while
each column represents a frequency channel for a given sample. Time is increasing from bottom to top while the frequency is
increasing from right to left.
Expected Barycentric spectra for +vrel
Time
f1 f2 f3 f4
Corrected Spectra with expansion
Time
f1 + f2 f
′
2 f
′
3 f
′
4
Expected Barycentric spectra for −vrel
Time
f1 f2 f3 f4
Corrected Frequency channels
Time
f
′
1
f1 + f2 f
′
3 f
′
4
Figure A.3. These plots depict the expected spectra at their respective barycentric frequencies and the spectra after the
correction for barycentric relative velocity. Each plot represents a single spectrum, where the frequency increases from right to
left. (a) In the case of +vrel, the first channel of the topocentric spectra is shifted to a higher barycentric frequency compared
to the last topocentric spectra channel, which causes an expansion of the spectra. If two consecutive channels move farther
away from each other (shown as f1 and f2) by more than half the channel width, an additional channel is added in between,
which is the summation of these two channels. Extra channels at the edge of the spectra are dropped. (b) In the case of −vrel,
the first channel of the topocentric frequency is shifted to a lower barycentric frequency relative to the last topocentric spectra
channel, which causes a squeeze in the spectra. If two consecutive frequency channels shift closer to each other by more than
half a channel width, these channels are added together and an extra channel is added at the end containing zeros. The bottom
spectra in each plot illustrate these expansion and squeeze effects after correction are applied from the code.
8 https://github.com/gajjarv/BaryCentricCorrection
18. 18 Johnson et al.
Input filterbank in topocentric frame
vrel 0
|vrel| ↑?
Shift to higher frequency Shift to lower frequency
Expand
|vrel| ↑?
Shift to lower frequency Shift to higher frequency
Squeeze
Output filterbank in barycentric frame
Yes
Yes No
No
Yes No
Figure A.4. An outline of the post-detection barycentric correction algorithm for an input filterbank file in sigproc format.
For this case, the input filterbank file has a descending order in frequency, and vrel represents the relative velocity between the
transmitter and observer. The algorithm considers two cases depending on whether the relative velocity is positive or negative,
which indicates whether the source is moving away from or towards the observer, respectively. Each of these cases is further
divided into two where the absolute value of the relative velocity can either increase or decrease, requiring the spectra to be
shifted to either the higher or lower frequency end. For all cases with +vrel, each spectra is expanded, and for −vrel, each
spectra is squeezed, as shown in Figure A.3. The code then writes each of these spectra into another sigproc filterbank file,
which will have each channel frequency closely corrected to the barycentric frame of reference.
B. SENSITIVITY OF THE SURVEY ACROSS THE HBA
As previously stated the high band antenna spans from 110 - 190 MHz. The system temperature across the band
significantly, which reduces the sensitivity of LOFAR at the lower end of the band-pass (see. Figure 10). Calculation
of Tsys and consquently SEFD follows a modified method as outlined in § 3.3 of McKenna et al. (2023b). The method
differs in the calculation of Tsky as this is pointing dependent. This study uses the LWA1 Low Frequency Sky Survey
(Dowell et al. 2017) for sensitivity analysis. We calculate system equivalent flux density (SEFD; Jy) as follows,
SEFD =
2Tsyskb
Ae
(B1)
Where kb is the Boltzmann constant and Ae is the effective collecting area of a single staion HBA. EIRP is then
consequently calculated using Equation (4).