We present here timing and spectral analyses of SGR J1830−0645 based on an AstroSat observation carried out on 2020 October
16, about a week after the onset of its first detected X-ray outburst. Using data taken with the Soft X-ray Telescope (SXT) and
Large Area X-ray Proportional Counter (LAXPC), we have detected 0.9–10 keV coherent pulsations at a period of ∼10.4 s.
The pulse profiles were single-peaked, asymmetric, and consisted of minor peaks attributable to hotspots on the neutron star
surface. The pulsed fraction evolved significantly with energy, increasing to energies around 5 keV with a steep drop thereafter.
The 0.9–25 keV SXT–LAXPC energy spectrum is best described with two thermal components having temperatures ∼0.46 and
∼1.1 keV (emission radii of ∼2.4 and ∼0.65 km, respectively, assuming a distance of 4 kpc) along with a power-law component
having a photon index of ∼0.39. We report the detection of 67 X-ray bursts having an average duration of ∼33 ms. The brightest
burst lasted for about 90 ms and had a 3–25 keV fluence of ∼5 × 10−9 erg cm−2.
Matter ejections behind the highs and lows of the transitional millisecond pu...Sérgio Sacani
Transitional millisecond pulsars are an emerging class of sources linking low-mass X-ray binaries to millisecond radio pulsars in
binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active
state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray
to optical pulsations are observed only during the high mode. Knowledge of the root reason for this puzzling behaviour remains
elusive. This paper presents the results of the most extensive multi-wavelength campaign ever conducted on the transitional pulsar
prototype, PSR J1023+0038, covering from radio to X-rays. The campaign was carried out over two nights in June 2021, and involved
12 different telescopes and instruments including XMM-Newton, HST, VLT/FORS2 (in polarimetric mode), ALMA, VLA and FAST.
By modelling the broadband spectral energy distributions in both emission modes, we show that the mode switches are caused by
changes in the innermost region of the accretion disc. These changes trigger the emission of discrete mass ejections, which occur on
top of a compact jet, as testified by the detection of at least one short-duration millimetre flare with A
Fast radio bursts trigger aftershocks resembling earthquakes, but not solar f...Sérgio Sacani
The production mechanism of repeating fast radio bursts (FRBs) is still a mystery, and correlations between burst occurrence
times and energies may provide important clues to elucidate it. While time correlation studies of FRBs have been mainly
performed using wait time distributions, here we report the results of a correlation function analysis of repeating FRBs in the
2D space of time and energy. We analyse nearly 7,000 bursts reported in the literature for the three most active sources of
FRB 20121102A, 20201124A, and 20220912A, and find the following characteristics that are universal in the three sources. A
clear power-law signal of the correlation function is seen, extending to the typical burst duration (∼ 10 msec) towards shorter
time intervals (t). The correlation function indicates that every single burst has about a 10–60 per cent chance of producing
an aftershock at a rate decaying by a power law as ∝ (t)
−p with p = 1.5–2.5, like the Omori–Utsu law of earthquakes. The
correlated aftershock rate is stable regardless of source activity changes, and there is no correlation between emitted energy
and t. We demonstrate that all these properties are quantitatively common to earthquakes, but different from solar flares in
many aspects, by applying the same analysis method for the data on these phenomena. These results suggest that repeater FRBs
are a phenomenon in which energy stored in rigid neutron star crusts is released by seismic activity. This may provide a new
opportunity for future studies to explore the physical properties of the neutron star crust.
X-RAY MEASUREMENTS OF THE PARTICLE ACCELERATION PROPERTIES AT INWARD SHOCKS I...Sérgio Sacani
We present new evidence that the bright non-thermal X-ray emission features in the interior of the Cassiopeia A
supernova remnant (SNR) are caused by inward moving shocks based on Chandra and NuSTAR observations. Several
bright inward-moving filaments were identified using monitoring data taken by Chandra in 2000–2014. These inwardmoving shock locations are nearly coincident with hard X-ray (15–40 keV) hot spots seen by NuSTAR. From proper
motion measurements, the transverse velocities were estimated to be in the range ∼2,100–3,800 km s−1
for a distance of
3.4 kpc. The shock velocities in the frame of the expanding ejecta reach values of ∼5,100–8,700 km s−1
, slightly higher
than the typical speed of the forward shock. Additionally, we find flux variations (both increasing and decreasing) on
timescales of a few years in some of the inward-moving shock filaments. The rapid variability timescales are consistent
with an amplified magnetic field of B ∼ 0.5–1 mG. The high speed and low photon cut-off energy of the inward-moving
shocks are shown to imply a particle diffusion coefficient that departs from the Bohm regime (k0 = D0/D0,Bohm ∼ 3–8)
for the few simple physical configurations we consider in this study. The maximum electron energy at these shocks is
estimated to be ∼8–11 TeV, smaller than the values of ∼15–34 TeV inferred for the forward shock. Cassiopeia A is
dynamically too young for its reverse shock to appear to be moving inward in the observer frame. We propose instead
that the inward-moving shocks are a consequence of the forward shock encountering a density jump of & 5–8 in the
surrounding material.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
Reionization and the ISM/Stellar Origins with JWST and ALMA (RIOJA): The Core...Sérgio Sacani
The protoclusters in the epoch of reionization, traced by galaxy overdensity regions, are ideal laboratories for
studying the process of stellar assembly and cosmic reionization. We present the spectroscopic confirmation of the
core of the most distant protocluster at z = 7.88, A2744-z7p9OD, with the James Webb Space Telescope NIRSpec
integral field unit spectroscopy. The core region includes as many as four galaxies detected in [O III] 4960 and
5008 Å in a small area of ∼3″ × 3″, corresponding to ∼11 × 11 kpc, after the lensing magnification correction.
Three member galaxies are also tentatively detected in dust continuum in Atacama Large Millimeter/submillimeter
Array Band 6, which is consistent with their red ultraviolet continuum slopes, β ∼ −1.3. The member galaxies
have stellar masses in the range of log(M*/Me) ∼7.6–9.2 and star formation rates of ∼3–50 Me yr−1
, showing a
diversity in their properties. FirstLight cosmological simulations reproduce the physical properties of the member
galaxies including the stellar mass, [O III] luminosity, and dust-to-stellar mass ratio, and predict that the member
galaxies are on the verge of merging in a few to several tens of Myr to become a large galaxy with
M* ∼ 6 × 109
Me. The presence of a multiple merger and evolved galaxies in the core region of A2744-z7p9OD
indicates that environmental effects are already at work 650 Myr after the Big Bang.
The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflectio...Sérgio Sacani
We present X-ray, UV, optical, and radio observations of the nearby (≈78 Mpc) tidal disruption event
AT2021ehb/ZTF21aanxhjv during its first 430 days of evolution. AT2021ehb occurs in the nucleus of a galaxy
hosting a≈107 Me black hole (MBH inferred from host galaxy scaling relations). High-cadence Swift and Neutron
Star Interior Composition Explorer (NICER) monitoring reveals a delayed X-ray brightening. The spectrum first
undergoes a gradual soft → hard transition and then suddenly turns soft again within 3 days at δt≈272 days during
which the X-ray flux drops by a factor of 10. In the joint NICER+NuSTAR observation (δt = 264 days, harder
state), we observe a prominent nonthermal component up to 30 keV and an extremely broad emission line in the
iron K band. The bolometric luminosity of AT2021ehb reaches a maximum of -
+ 6.0 % 3.8 L 10.4
Edd when the X-ray
spectrum is the hardest. During the dramatic X-ray evolution, no radio emission is detected, the UV/optical
luminosity stays relatively constant, and the optical spectra are featureless. We propose the following
interpretations: (i) the soft → hard transition may be caused by the gradual formation of a magnetically
dominated corona; (ii) hard X-ray photons escape from the system along solid angles with low scattering optical
depth (∼a few) whereas the UV/optical emission is likely generated by reprocessing materials with much larger
column density—the system is highly aspherical; and (iii) the abrupt X-ray flux drop may be triggered by the
thermal–viscous instability in the inner accretion flow, leading to a much thinner disk.
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 atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
Matter ejections behind the highs and lows of the transitional millisecond pu...Sérgio Sacani
Transitional millisecond pulsars are an emerging class of sources linking low-mass X-ray binaries to millisecond radio pulsars in
binary systems. These pulsars alternate between a radio pulsar state and an active low-luminosity X-ray disc state. During the active
state, these sources exhibit two distinct emission modes (high and low) that alternate unpredictably, abruptly, and incessantly. X-ray
to optical pulsations are observed only during the high mode. Knowledge of the root reason for this puzzling behaviour remains
elusive. This paper presents the results of the most extensive multi-wavelength campaign ever conducted on the transitional pulsar
prototype, PSR J1023+0038, covering from radio to X-rays. The campaign was carried out over two nights in June 2021, and involved
12 different telescopes and instruments including XMM-Newton, HST, VLT/FORS2 (in polarimetric mode), ALMA, VLA and FAST.
By modelling the broadband spectral energy distributions in both emission modes, we show that the mode switches are caused by
changes in the innermost region of the accretion disc. These changes trigger the emission of discrete mass ejections, which occur on
top of a compact jet, as testified by the detection of at least one short-duration millimetre flare with A
Fast radio bursts trigger aftershocks resembling earthquakes, but not solar f...Sérgio Sacani
The production mechanism of repeating fast radio bursts (FRBs) is still a mystery, and correlations between burst occurrence
times and energies may provide important clues to elucidate it. While time correlation studies of FRBs have been mainly
performed using wait time distributions, here we report the results of a correlation function analysis of repeating FRBs in the
2D space of time and energy. We analyse nearly 7,000 bursts reported in the literature for the three most active sources of
FRB 20121102A, 20201124A, and 20220912A, and find the following characteristics that are universal in the three sources. A
clear power-law signal of the correlation function is seen, extending to the typical burst duration (∼ 10 msec) towards shorter
time intervals (t). The correlation function indicates that every single burst has about a 10–60 per cent chance of producing
an aftershock at a rate decaying by a power law as ∝ (t)
−p with p = 1.5–2.5, like the Omori–Utsu law of earthquakes. The
correlated aftershock rate is stable regardless of source activity changes, and there is no correlation between emitted energy
and t. We demonstrate that all these properties are quantitatively common to earthquakes, but different from solar flares in
many aspects, by applying the same analysis method for the data on these phenomena. These results suggest that repeater FRBs
are a phenomenon in which energy stored in rigid neutron star crusts is released by seismic activity. This may provide a new
opportunity for future studies to explore the physical properties of the neutron star crust.
X-RAY MEASUREMENTS OF THE PARTICLE ACCELERATION PROPERTIES AT INWARD SHOCKS I...Sérgio Sacani
We present new evidence that the bright non-thermal X-ray emission features in the interior of the Cassiopeia A
supernova remnant (SNR) are caused by inward moving shocks based on Chandra and NuSTAR observations. Several
bright inward-moving filaments were identified using monitoring data taken by Chandra in 2000–2014. These inwardmoving shock locations are nearly coincident with hard X-ray (15–40 keV) hot spots seen by NuSTAR. From proper
motion measurements, the transverse velocities were estimated to be in the range ∼2,100–3,800 km s−1
for a distance of
3.4 kpc. The shock velocities in the frame of the expanding ejecta reach values of ∼5,100–8,700 km s−1
, slightly higher
than the typical speed of the forward shock. Additionally, we find flux variations (both increasing and decreasing) on
timescales of a few years in some of the inward-moving shock filaments. The rapid variability timescales are consistent
with an amplified magnetic field of B ∼ 0.5–1 mG. The high speed and low photon cut-off energy of the inward-moving
shocks are shown to imply a particle diffusion coefficient that departs from the Bohm regime (k0 = D0/D0,Bohm ∼ 3–8)
for the few simple physical configurations we consider in this study. The maximum electron energy at these shocks is
estimated to be ∼8–11 TeV, smaller than the values of ∼15–34 TeV inferred for the forward shock. Cassiopeia A is
dynamically too young for its reverse shock to appear to be moving inward in the observer frame. We propose instead
that the inward-moving shocks are a consequence of the forward shock encountering a density jump of & 5–8 in the
surrounding material.
EXTINCTION AND THE DIMMING OF KIC 8462852Sérgio Sacani
To test alternative hypotheses for the behavior of KIC 8462852, we obtained measurements of the star
over a wide wavelength range from the UV to the mid-infrared from October 2015 through December
2016, using Swift, Spitzer and at AstroLAB IRIS. The star faded in a manner similar to the longterm
fading seen in Kepler data about 1400 days previously. The dimming rate for the entire period
reported is 22.1 ± 9.7 milli-mag yr−1
in the Swift wavebands, with amounts of 21.0 ± 4.5 mmag in
the groundbased B measurements, 14.0 ± 4.5 mmag in V , and 13.0 ± 4.5 in R, and a rate of 5.0 ± 1.2
mmag yr−1 averaged over the two warm Spitzer bands. Although the dimming is small, it is seen at
& 3 σ by three different observatories operating from the UV to the IR. The presence of long-term
secular dimming means that previous SED models of the star based on photometric measurements
taken years apart may not be accurate. We find that stellar models with Tef f = 7000 - 7100 K and
AV ∼ 0.73 best fit the Swift data from UV to optical. These models also show no excess in the
near-simultaneous Spitzer photometry at 3.6 and 4.5 µm, although a longer wavelength excess from
a substantial debris disk is still possible (e.g., as around Fomalhaut). The wavelength dependence of
the fading favors a relatively neutral color (i.e., RV & 5, but not flat across all the bands) compared
with the extinction law for the general ISM (RV = 3.1), suggesting that the dimming arises from
circumstellar material
Reionization and the ISM/Stellar Origins with JWST and ALMA (RIOJA): The Core...Sérgio Sacani
The protoclusters in the epoch of reionization, traced by galaxy overdensity regions, are ideal laboratories for
studying the process of stellar assembly and cosmic reionization. We present the spectroscopic confirmation of the
core of the most distant protocluster at z = 7.88, A2744-z7p9OD, with the James Webb Space Telescope NIRSpec
integral field unit spectroscopy. The core region includes as many as four galaxies detected in [O III] 4960 and
5008 Å in a small area of ∼3″ × 3″, corresponding to ∼11 × 11 kpc, after the lensing magnification correction.
Three member galaxies are also tentatively detected in dust continuum in Atacama Large Millimeter/submillimeter
Array Band 6, which is consistent with their red ultraviolet continuum slopes, β ∼ −1.3. The member galaxies
have stellar masses in the range of log(M*/Me) ∼7.6–9.2 and star formation rates of ∼3–50 Me yr−1
, showing a
diversity in their properties. FirstLight cosmological simulations reproduce the physical properties of the member
galaxies including the stellar mass, [O III] luminosity, and dust-to-stellar mass ratio, and predict that the member
galaxies are on the verge of merging in a few to several tens of Myr to become a large galaxy with
M* ∼ 6 × 109
Me. The presence of a multiple merger and evolved galaxies in the core region of A2744-z7p9OD
indicates that environmental effects are already at work 650 Myr after the Big Bang.
The Tidal Disruption Event AT2021ehb: Evidence of Relativistic Disk Reflectio...Sérgio Sacani
We present X-ray, UV, optical, and radio observations of the nearby (≈78 Mpc) tidal disruption event
AT2021ehb/ZTF21aanxhjv during its first 430 days of evolution. AT2021ehb occurs in the nucleus of a galaxy
hosting a≈107 Me black hole (MBH inferred from host galaxy scaling relations). High-cadence Swift and Neutron
Star Interior Composition Explorer (NICER) monitoring reveals a delayed X-ray brightening. The spectrum first
undergoes a gradual soft → hard transition and then suddenly turns soft again within 3 days at δt≈272 days during
which the X-ray flux drops by a factor of 10. In the joint NICER+NuSTAR observation (δt = 264 days, harder
state), we observe a prominent nonthermal component up to 30 keV and an extremely broad emission line in the
iron K band. The bolometric luminosity of AT2021ehb reaches a maximum of -
+ 6.0 % 3.8 L 10.4
Edd when the X-ray
spectrum is the hardest. During the dramatic X-ray evolution, no radio emission is detected, the UV/optical
luminosity stays relatively constant, and the optical spectra are featureless. We propose the following
interpretations: (i) the soft → hard transition may be caused by the gradual formation of a magnetically
dominated corona; (ii) hard X-ray photons escape from the system along solid angles with low scattering optical
depth (∼a few) whereas the UV/optical emission is likely generated by reprocessing materials with much larger
column density—the system is highly aspherical; and (iii) the abrupt X-ray flux drop may be triggered by the
thermal–viscous instability in the inner accretion flow, leading to a much thinner disk.
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 atacama cosmology_telescope_measuring_radio_galaxy_bias_through_cross_cor...Sérgio Sacani
A radiação cósmica de micro-ondas aponta para a matéria escura invisível, marcando o ponto onde jatos de material viajam a velocidades próximas da velocidade da luz, de acordo com uma equipe internacional de astrônomos. O principal autor do estudo, Rupert Allison da Universidade de Oxford apresentou os resultados no dia 6 de Julho de 2015 no National Astronomy Meeting em Venue Cymru, em Llandudno em Wales.
Atualmente, ninguém sabe ao certo do que a matéria escura é feita, mas ela é responsável por cerca de 26% do conteúdo de energia do universo, com galáxias massivas se formando em densas regiões de matéria escura. Embora invisível, a matéria escura se mostra através do efeito gravitacional – uma grande bolha de matéria escura puxa a matéria normal (como elétrons, prótons e nêutrons) através de sua própria gravidade, eventualmente se empacotando conjuntamente para criar as estrelas e galáxias inteiras.
Muitas das maiores dessas são galáxias ativas com buracos negros supermassivos em seus centros. Alguma parte do gás caindo diretamente na direção do buraco negro é ejetada como jatos de partículas e radiação. As observações feitas com rádio telescópios mostram que esses jatos as vezes se espalham por milhões de anos-luz desde a galáxia – mais distante até mesmo do que a extensão da própria galáxia.
Os cientistas esperam que os jatos possam viver em regiões onde existe um excesso de concentração da matéria escura, maior do que o da média. Mas como a matéria escura é invisível, testar essa ideia não é algo tão direto.
GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process N...Sérgio Sacani
Fast neutron-rich material ejected dynamically over 10 ms during the merger of a binary neutron star (BNS) can
give rise to distinctive electromagnetic counterparts to the system’s gravitational-wave emission that serve as a
“smoking gun” to distinguish between a BNS and an NS–black hole merger. We present novel ab initio modeling
of the kilonova precursor and kilonova afterglow based on 3D general-relativistic magnetohydrodynamic
simulations of BNS mergers with nuclear, tabulated, finite-temperature equations of state (EOSs), weak
interactions, and approximate neutrino transport. We analyze dynamical mass ejection from 1.35–1.35 Me
binaries, consistent with properties of the first observed BNS merger GW170817, using three nuclear EOSs that
span the range of allowed compactness of 1.35 Me-neutron stars. Nuclear reaction network calculations yield a
robust second-to-third-peak r-process. We find few ×10−6 Me of fast (v > 0.6c) ejecta that give rise to broadband
synchrotron emission on ∼years timescales, consistent with tentative evidence for excess X-ray/radio emission
following GW170817. We find ≈2 × 10−5 Me of free neutrons that power a kilonova precursor on hours
timescale. A boost in early UV/optical brightness by a factor of a few due to previously neglected relativistic
effects, with enhancements up to 10 hr post-merger, is promising for future detection with UV/optical telescopes
like Swift or ULTRASAT. We find that a recently predicted opacity boost due to highly ionized lanthanides at
70,000 K is unlikely to affect the early kilonova based on the obtained ejecta structures. Azimuthal
inhomogeneities in dynamical ejecta composition for soft EOSs found here (“lanthanide/actinide pockets”) may
have observable consequences for both early kilonova and late-time nebular emission.
Flaring from the_supermassive_black_hole_in_mrk335_studied_with_swift_and_nustarSérgio Sacani
Os comportamentos estranhos e desconcertantes dos buracos negros tornam-se cada dia menos misteriosos, com as novas observações feitas com as missões Swift e NuSTAR da NASA. Os dois telescópios espaciais registraram um buraco negro supermassivo no meio de uma gigantesca explosão de luz de raio-X, ajudando os astrônomos a tentarem resolver um grande quebra-cabeça: Como os buracos negros supermassivos emitem flares?
Os resultados sugerem que os buracos negros supermassivos emitem flares de raios-X, quando suas coroas circundantes, fontes de partículas extremamente energéticas, são atiradas ou lançadas para fora dos buracos negros.
“Essa é a primeira vez que nós somos capazes de linkar o lançamento da coroa com uma flare”, disse Dan Wilkins, da Universidade de Saint Mary em Halifax, no Canadá e principal autor do artigo que descreve os resultados na revista Monthly Notices of The Royal Astronomical Society. “Isso nos ajudará a entender como os buracos negros supermassivos alimentam alguns dos objetos mais brilhantes do universo”.
Os buracos negros supermassivos não emitem luz por si só, mas eles as vezes são circundados por discos de material quente e brilhante. A gravidade do buraco negro puxa o gás ao redor, aquecendo esse material e fazendo com que ele brilhe com diferentes tipos de luz. Outra fonte da radiação perto do buraco negro é a coroa. As coroas são feitas de partículas altamente energéticas que geram luz de raio-X, mas os detalhes sobre sua aparência, ou como elas se formam, ainda não são claros.
A High-mass, Young Star-forming Core Escaping from Its Parental FilamentSérgio Sacani
We studied the unique kinematic properties in massive filament G352.63-1.07 at 103 au spatial scale with the dense
molecular tracers observed with the Atacama Large Millimeter/submillimeter Array. We find the central massive
core M1 (12 Me) being separated from the surrounding filament with a velocity difference of
- =- - v vsys 2 km s 1 and a transverse separation within 3″. Meanwhile, as shown in multiple dense-gas
tracers, M1 has a spatial extension closely aligned with the main filament and is connected to the filament toward
both its ends. M1 thus represents a very beginning state for a massive, young star-forming core escaping from the
parental filament, within a timescale of ∼4000 yr. Based on its kinetic energy (3.5 × 1044 erg), the core escape is
unlikely solely due to the original filament motion or magnetic field but requires more energetic events such as a
rapid intense anisotropic collapse. The released energy also seems to noticeably increase the environmental
turbulence. This may help the filament to become stabilized again.
Solving the Multimessenger Puzzle of the AGN-starburst Composite Galaxy NGC 1068Sérgio Sacani
Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from
their central region. These active galactic nuclei (AGN)-starburst composites are of special interest, as both
phenomena on their own are potential sources of highly energetic cosmic rays and associated γ-ray and neutrino
emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission
from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the
case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we
show that the entire spectrum of multimessenger data—from radio to γ-rays including the neutrino constraint—can
be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission
region is not sufficient.
ALMA Observations of the Extraordinary Carina Pillars: A Complementary SampleSérgio Sacani
We present a study of six dusty and gaseous pillars (containing the HH 1004 and HH 1010 objects)
and globules (that contain the HH 666, HH 900, HH 1006, and HH 1066 objects) localized in the Carina
nebula using sensitive and high angular resolution (∼0.3′′) Atacama Large Millimeter/Sub-millimeter
Array (ALMA) observations. This is a more extensive study that the one presented in Cortes-Rangel
et al. (2020). As in this former study, we also analyzed the 1.3 mm continuum emission and C18O(2−1),
N2D+(3−2) and 12CO(2−1) spectral lines. These new observations revealed the molecular outflows
emanating from the pillars, the dusty envelopes+disks that are exciting them, and the extended HH
objects far from their respective pillars. We reveal that the masses of the disks+envelopes are in a
range of 0.02 to 0.38 M⊙, and those for the molecular outflows are of the order of 10−3 M⊙, which
suggests that their exciting sources might be low- or intermediate-mass protostars as already revealed
in recent studies at infrared and submillimeter bands. In the regions associated with the objects HH
900 and HH 1004, we report multiple millimeter continuum sources, from where several molecular
outflows emanate.
PROBING THE SOLAR INTERIOR WITH LENSED GRAVITATIONAL WAVES FROM KNOWN PULSARSSérgio Sacani
When gravitational waves (GWs) from a spinning neutron star arrive from behind the Sun, they are
subjected to gravitational lensing that imprints a frequency-dependent modulation on the waveform.
This modulation traces the projected solar density and gravitational potential along the path as
the Sun passes in front of the neutron star. We calculate how accurately the solar density prole
can be extracted from the lensed GWs using a Fisher analysis. For this purpose, we selected three
promising candidates (the highly spinning pulsars J1022+1001, J1730-2304, and J1745-23) from the
pulsar catalog of the Australia Telescope National Facility. The lensing signature can be measured
with 3 condence when the signal-to-noise ratio (SNR) of the GW detection reaches 100 (f=300Hz)1
over a one-year observation period (where f is the GW frequency). The solar density prole can be
plotted as a function of radius when the SNR improves to & 104.
Fifteen years of_xmm_newton_and_chandra_monitoring_of_sgr_a_evidence_for_a_re...Sérgio Sacani
Três telescópios de raios-X têm monitorado o buraco negro supermassivo no centro da Via Láctea, na última década e meia observando o seu comportamento. Essa longa campanha de monitoramento tem revelado algumas novas mudanças nos padrões desse buraco negro de 4 milhões de massas solares conhecido como Sagittarius A* (Sgr A*).
O painel inferior do gráfico principal desse post é uma visão da região ao redor do Sgr A*, onde as cores vermelha, verde e azul, representam os raios-X de baixa, média e alta energia detectados pelo Observatório de Raios-X Chandra da NASA. O Sgr A* não é visto na imagem, mas ele está mergulhado no ponto brando na ponta final da seta. Os outros dois telescópios envolvidos nessas observações de raios-X de 15 anos foram o XMM-Newton da ESA e o Swift Gamma Ray Burst Explorer da NASA, mas seus dados não estão incluídos nessa imagem.
Dentro do último ano, o buraco negro normalmente tranquilo, tem mostrado um aumento no nível de flares de raios-X com relação à sua taxa típica. Esse aumento nos flares de raios-X coincide com a passagem perto do Sgr A* do misterioso objeto chamado G2. Os astrônomos estão rastreando o G2 por anos, pensado originalmente como uma extensa nuvem de gás e poeira. Contudo, depois da passagem próxima do Sgr A* no final de 2013 sua aparência não mudou muito, a menos do fato de ter sido levemente estirado pela gravidade do buraco negro. Isso levou a novas teorias que o G2 não era uma nuvem de gás, mas uma estrela ou um par de estrelas dentro de um casulo empoeirado.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
The JWST Discovery of the Triply-imaged Type Ia “Supernova H0pe” and Observat...Sérgio Sacani
A Type Ia supernova (SN) at z = 1.78 was discovered in James Webb Space Telescope Near Infrared
Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; z = 0.35). The SN is situated 1.5–
2 kpc from its host galaxy Arc 2 and appears in three different locations as a result of gravitational
lensing by G165. These data can yield a value for Hubble’s constant using time delays from this
multiply-imaged SN Ia that we call “SN H0pe.” Over the entire field we identified 21 image multiplicities,
confirmed five of them using Near-Infrared Spectrograph (NIRspec), and constructed a new
lens model that gives a total mass within 600 kpc of (2.6 ± 0.3) × 1014M⊙. The photometry uncovered
a galaxy overdensity at Arc 2’s redshift. NIRSpec confirmed six member galaxies, four of which
surround Arc 2 with relative velocity ≲900 km s−1 and projected physical extent ≲33 kpc. Arc 2
dominates the stellar mass ((5.0±0.1)×1011M⊙), which is a factor of ten higher than other members
of this compact galaxy group. These other group members have specific star formation rates (sSFR)
arXiv:2309.07326v1 [astro-ph.GA] 13 Sep 2023
2 Frye, Pascale, Pierel et al.
of 2–260 Gyr−1 derived from the Hα-line flux corrected for stellar absorption, dust extinction, and slit
losses. Another group centered on the dusty star forming galaxy Arc 1 is at z = 2.24. The total SFR
for the Arc 1 group (≳400M⊙ yr−1) translates to a supernova rate of ∼1 SNe yr−1, suggesting that
regular monitoring of this cluster may yield additional SNe.
Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Gal...Sérgio Sacani
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key
insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric
shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here,
we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field
covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope.
From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis
(connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of
M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and
twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy.
Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine
simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar
mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of
p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine
the black hole mass to be ( - ´) 5.37 0.22 10 +
0.25
0.37 9M , where the second error indicates the systematic uncertainty
associated with the distance to M87.
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.
More Related Content
Similar to AstroSat observation of the magnetar SGR J1830−0645 during its first detected X-ray outburst
GRMHD Simulations of Neutron-star Mergers with Weak Interactions: r-process N...Sérgio Sacani
Fast neutron-rich material ejected dynamically over 10 ms during the merger of a binary neutron star (BNS) can
give rise to distinctive electromagnetic counterparts to the system’s gravitational-wave emission that serve as a
“smoking gun” to distinguish between a BNS and an NS–black hole merger. We present novel ab initio modeling
of the kilonova precursor and kilonova afterglow based on 3D general-relativistic magnetohydrodynamic
simulations of BNS mergers with nuclear, tabulated, finite-temperature equations of state (EOSs), weak
interactions, and approximate neutrino transport. We analyze dynamical mass ejection from 1.35–1.35 Me
binaries, consistent with properties of the first observed BNS merger GW170817, using three nuclear EOSs that
span the range of allowed compactness of 1.35 Me-neutron stars. Nuclear reaction network calculations yield a
robust second-to-third-peak r-process. We find few ×10−6 Me of fast (v > 0.6c) ejecta that give rise to broadband
synchrotron emission on ∼years timescales, consistent with tentative evidence for excess X-ray/radio emission
following GW170817. We find ≈2 × 10−5 Me of free neutrons that power a kilonova precursor on hours
timescale. A boost in early UV/optical brightness by a factor of a few due to previously neglected relativistic
effects, with enhancements up to 10 hr post-merger, is promising for future detection with UV/optical telescopes
like Swift or ULTRASAT. We find that a recently predicted opacity boost due to highly ionized lanthanides at
70,000 K is unlikely to affect the early kilonova based on the obtained ejecta structures. Azimuthal
inhomogeneities in dynamical ejecta composition for soft EOSs found here (“lanthanide/actinide pockets”) may
have observable consequences for both early kilonova and late-time nebular emission.
Flaring from the_supermassive_black_hole_in_mrk335_studied_with_swift_and_nustarSérgio Sacani
Os comportamentos estranhos e desconcertantes dos buracos negros tornam-se cada dia menos misteriosos, com as novas observações feitas com as missões Swift e NuSTAR da NASA. Os dois telescópios espaciais registraram um buraco negro supermassivo no meio de uma gigantesca explosão de luz de raio-X, ajudando os astrônomos a tentarem resolver um grande quebra-cabeça: Como os buracos negros supermassivos emitem flares?
Os resultados sugerem que os buracos negros supermassivos emitem flares de raios-X, quando suas coroas circundantes, fontes de partículas extremamente energéticas, são atiradas ou lançadas para fora dos buracos negros.
“Essa é a primeira vez que nós somos capazes de linkar o lançamento da coroa com uma flare”, disse Dan Wilkins, da Universidade de Saint Mary em Halifax, no Canadá e principal autor do artigo que descreve os resultados na revista Monthly Notices of The Royal Astronomical Society. “Isso nos ajudará a entender como os buracos negros supermassivos alimentam alguns dos objetos mais brilhantes do universo”.
Os buracos negros supermassivos não emitem luz por si só, mas eles as vezes são circundados por discos de material quente e brilhante. A gravidade do buraco negro puxa o gás ao redor, aquecendo esse material e fazendo com que ele brilhe com diferentes tipos de luz. Outra fonte da radiação perto do buraco negro é a coroa. As coroas são feitas de partículas altamente energéticas que geram luz de raio-X, mas os detalhes sobre sua aparência, ou como elas se formam, ainda não são claros.
A High-mass, Young Star-forming Core Escaping from Its Parental FilamentSérgio Sacani
We studied the unique kinematic properties in massive filament G352.63-1.07 at 103 au spatial scale with the dense
molecular tracers observed with the Atacama Large Millimeter/submillimeter Array. We find the central massive
core M1 (12 Me) being separated from the surrounding filament with a velocity difference of
- =- - v vsys 2 km s 1 and a transverse separation within 3″. Meanwhile, as shown in multiple dense-gas
tracers, M1 has a spatial extension closely aligned with the main filament and is connected to the filament toward
both its ends. M1 thus represents a very beginning state for a massive, young star-forming core escaping from the
parental filament, within a timescale of ∼4000 yr. Based on its kinetic energy (3.5 × 1044 erg), the core escape is
unlikely solely due to the original filament motion or magnetic field but requires more energetic events such as a
rapid intense anisotropic collapse. The released energy also seems to noticeably increase the environmental
turbulence. This may help the filament to become stabilized again.
Solving the Multimessenger Puzzle of the AGN-starburst Composite Galaxy NGC 1068Sérgio Sacani
Multiwavelength observations indicate that some starburst galaxies show a dominant nonthermal contribution from
their central region. These active galactic nuclei (AGN)-starburst composites are of special interest, as both
phenomena on their own are potential sources of highly energetic cosmic rays and associated γ-ray and neutrino
emission. In this work, a homogeneous, steady-state two-zone multimessenger model of the nonthermal emission
from the AGN corona as well as the circumnuclear starburst region is developed and subsequently applied to the
case of NGC 1068, which has recently shown some first indications of high-energy neutrino emission. Here, we
show that the entire spectrum of multimessenger data—from radio to γ-rays including the neutrino constraint—can
be described very well if both, starburst and AGN corona, are taken into account. Using only a single emission
region is not sufficient.
ALMA Observations of the Extraordinary Carina Pillars: A Complementary SampleSérgio Sacani
We present a study of six dusty and gaseous pillars (containing the HH 1004 and HH 1010 objects)
and globules (that contain the HH 666, HH 900, HH 1006, and HH 1066 objects) localized in the Carina
nebula using sensitive and high angular resolution (∼0.3′′) Atacama Large Millimeter/Sub-millimeter
Array (ALMA) observations. This is a more extensive study that the one presented in Cortes-Rangel
et al. (2020). As in this former study, we also analyzed the 1.3 mm continuum emission and C18O(2−1),
N2D+(3−2) and 12CO(2−1) spectral lines. These new observations revealed the molecular outflows
emanating from the pillars, the dusty envelopes+disks that are exciting them, and the extended HH
objects far from their respective pillars. We reveal that the masses of the disks+envelopes are in a
range of 0.02 to 0.38 M⊙, and those for the molecular outflows are of the order of 10−3 M⊙, which
suggests that their exciting sources might be low- or intermediate-mass protostars as already revealed
in recent studies at infrared and submillimeter bands. In the regions associated with the objects HH
900 and HH 1004, we report multiple millimeter continuum sources, from where several molecular
outflows emanate.
PROBING THE SOLAR INTERIOR WITH LENSED GRAVITATIONAL WAVES FROM KNOWN PULSARSSérgio Sacani
When gravitational waves (GWs) from a spinning neutron star arrive from behind the Sun, they are
subjected to gravitational lensing that imprints a frequency-dependent modulation on the waveform.
This modulation traces the projected solar density and gravitational potential along the path as
the Sun passes in front of the neutron star. We calculate how accurately the solar density prole
can be extracted from the lensed GWs using a Fisher analysis. For this purpose, we selected three
promising candidates (the highly spinning pulsars J1022+1001, J1730-2304, and J1745-23) from the
pulsar catalog of the Australia Telescope National Facility. The lensing signature can be measured
with 3 condence when the signal-to-noise ratio (SNR) of the GW detection reaches 100 (f=300Hz)1
over a one-year observation period (where f is the GW frequency). The solar density prole can be
plotted as a function of radius when the SNR improves to & 104.
Fifteen years of_xmm_newton_and_chandra_monitoring_of_sgr_a_evidence_for_a_re...Sérgio Sacani
Três telescópios de raios-X têm monitorado o buraco negro supermassivo no centro da Via Láctea, na última década e meia observando o seu comportamento. Essa longa campanha de monitoramento tem revelado algumas novas mudanças nos padrões desse buraco negro de 4 milhões de massas solares conhecido como Sagittarius A* (Sgr A*).
O painel inferior do gráfico principal desse post é uma visão da região ao redor do Sgr A*, onde as cores vermelha, verde e azul, representam os raios-X de baixa, média e alta energia detectados pelo Observatório de Raios-X Chandra da NASA. O Sgr A* não é visto na imagem, mas ele está mergulhado no ponto brando na ponta final da seta. Os outros dois telescópios envolvidos nessas observações de raios-X de 15 anos foram o XMM-Newton da ESA e o Swift Gamma Ray Burst Explorer da NASA, mas seus dados não estão incluídos nessa imagem.
Dentro do último ano, o buraco negro normalmente tranquilo, tem mostrado um aumento no nível de flares de raios-X com relação à sua taxa típica. Esse aumento nos flares de raios-X coincide com a passagem perto do Sgr A* do misterioso objeto chamado G2. Os astrônomos estão rastreando o G2 por anos, pensado originalmente como uma extensa nuvem de gás e poeira. Contudo, depois da passagem próxima do Sgr A* no final de 2013 sua aparência não mudou muito, a menos do fato de ter sido levemente estirado pela gravidade do buraco negro. Isso levou a novas teorias que o G2 não era uma nuvem de gás, mas uma estrela ou um par de estrelas dentro de um casulo empoeirado.
Todo mundo sabe que os raios produzidos pela Estrela da Morte em Guerra nas Estrelas não pode existir na vida real, porém no universo existem fenômenos que as vezes conseguem superar até a mais surpreendente ficção.
A galáxia Pictor A, é um desses objetos que possuem fenômenos tão espetaculares quanto aqueles exibidos no cinema. Essa galáxia localiza-se a cerca de 500 milhões de anos-luz da Terra e possui um buraco negro supermassivo no seu centro. Uma grande quantidade de energia gravitacional é lançada, à medida que o material cai em direção ao horizonte de eventos, o ponto sem volta ao redor do buraco negro. Essa energia produz um enorme jato de partículas que viajam a uma velocidade próxima da velocidade da luz no espaço intergaláctico, chamado de jato relativístico.
Para obter imagens desse jato, os cientistas usaram o Observatório de Raios-X Chandra, da NASA várias vezes durante 15 anos. Os dados do Chandra, apresentados em azul nas imagens, foram combinados com os dados obtidos em ondas de rádio a partir do Australia Telescope Compact Array, e são aparesentados em vermelho nas imagens.
M82 X-2 is the first pulsating ultraluminous X-ray source discovered. The luminosity of these extreme pulsars, if
isotropic, implies an extreme mass transfer rate. An alternative is to assume a much lower mass transfer rate, but
with an apparent luminosity boosted by geometrical beaming. Only an independent measurement of the mass
transfer rate can help discriminate between these two scenarios. In this paper, we follow the orbit of the neutron star
for 7 yr, measure the decay of the orbit (P P orb orb 8 10 yr 6 1 · » - - - ), and argue that this orbital decay is driven by
extreme mass transfer of more than 150 times the mass transfer limit set by the Eddington luminosity. If this is true,
the mass available to the accretor is more than enough to justify its luminosity, with no need for beaming. This also
strongly favors models where the accretor is a highly magnetized neutron star.
The JWST Discovery of the Triply-imaged Type Ia “Supernova H0pe” and Observat...Sérgio Sacani
A Type Ia supernova (SN) at z = 1.78 was discovered in James Webb Space Telescope Near Infrared
Camera imaging of the galaxy cluster PLCK G165.7+67.0 (G165; z = 0.35). The SN is situated 1.5–
2 kpc from its host galaxy Arc 2 and appears in three different locations as a result of gravitational
lensing by G165. These data can yield a value for Hubble’s constant using time delays from this
multiply-imaged SN Ia that we call “SN H0pe.” Over the entire field we identified 21 image multiplicities,
confirmed five of them using Near-Infrared Spectrograph (NIRspec), and constructed a new
lens model that gives a total mass within 600 kpc of (2.6 ± 0.3) × 1014M⊙. The photometry uncovered
a galaxy overdensity at Arc 2’s redshift. NIRSpec confirmed six member galaxies, four of which
surround Arc 2 with relative velocity ≲900 km s−1 and projected physical extent ≲33 kpc. Arc 2
dominates the stellar mass ((5.0±0.1)×1011M⊙), which is a factor of ten higher than other members
of this compact galaxy group. These other group members have specific star formation rates (sSFR)
arXiv:2309.07326v1 [astro-ph.GA] 13 Sep 2023
2 Frye, Pascale, Pierel et al.
of 2–260 Gyr−1 derived from the Hα-line flux corrected for stellar absorption, dust extinction, and slit
losses. Another group centered on the dusty star forming galaxy Arc 1 is at z = 2.24. The total SFR
for the Arc 1 group (≳400M⊙ yr−1) translates to a supernova rate of ∼1 SNe yr−1, suggesting that
regular monitoring of this cluster may yield additional SNe.
Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Gal...Sérgio Sacani
The three-dimensional intrinsic shape of a galaxy and the mass of the central supermassive black hole provide key
insight into the galaxy’s growth history over cosmic time. Standard assumptions of a spherical or axisymmetric
shape can be simplistic and can bias the black hole mass inferred from the motions of stars within a galaxy. Here,
we present spatially resolved stellar kinematics of M87 over a two-dimensional 250″ × 300″ contiguous field
covering a radial range of 50 pc–12 kpc from integral-field spectroscopic observations at the Keck II Telescope.
From about 5 kpc and outward, we detect a prominent 25 km s−1 rotational pattern, in which the kinematic axis
(connecting the maximal receding and approaching velocities) is 40° misaligned with the photometric major axis of
M87. The rotational amplitude and misalignment angle both decrease in the inner 5 kpc. Such misaligned and
twisted velocity fields are a hallmark of triaxiality, indicating that M87 is not an axisymmetrically shaped galaxy.
Triaxial Schwarzschild orbit modeling with more than 4000 observational constraints enabled us to determine
simultaneously the shape and mass parameters. The models incorporate a radially declining profile for the stellar
mass-to-light ratio suggested by stellar population studies. We find that M87 is strongly triaxial, with ratios of
p = 0.845 for the middle-to-long principal axes and q = 0.722 for the short-to-long principal axes, and determine
the black hole mass to be ( - ´) 5.37 0.22 10 +
0.25
0.37 9M , where the second error indicates the systematic uncertainty
associated with the distance to M87.
Similar to AstroSat observation of the magnetar SGR J1830−0645 during its first detected X-ray outburst (20)
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.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
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.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
DERIVATION OF MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMINAL V...Wasswaderrick3
In this book, we use conservation of energy techniques on a fluid element to derive the Modified Bernoulli equation of flow with viscous or friction effects. We derive the general equation of flow/ velocity and then from this we derive the Pouiselle flow equation, the transition flow equation and the turbulent flow equation. In the situations where there are no viscous effects , the equation reduces to the Bernoulli equation. From experimental results, we are able to include other terms in the Bernoulli equation. We also look at cases where pressure gradients exist. We use the Modified Bernoulli equation to derive equations of flow rate for pipes of different cross sectional areas connected together. We also extend our techniques of energy conservation to a sphere falling in a viscous medium under the effect of gravity. We demonstrate Stokes equation of terminal velocity and turbulent flow equation. We look at a way of calculating the time taken for a body to fall in a viscous medium. We also look at the general equation of terminal velocity.
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
Salas, V. (2024) "John of St. Thomas (Poinsot) on the Science of Sacred Theol...Studia Poinsotiana
I Introduction
II Subalternation and Theology
III Theology and Dogmatic Declarations
IV The Mixed Principles of Theology
V Virtual Revelation: The Unity of Theology
VI Theology as a Natural Science
VII Theology’s Certitude
VIII Conclusion
Notes
Bibliography
All the contents are fully attributable to the author, Doctor Victor Salas. Should you wish to get this text republished, get in touch with the author or the editorial committee of the Studia Poinsotiana. Insofar as possible, we will be happy to broker your contact.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
Remote Sensing and Computational, Evolutionary, Supercomputing, and Intellige...University of Maribor
Slides from talk:
Aleš Zamuda: Remote Sensing and Computational, Evolutionary, Supercomputing, and Intelligent Systems.
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Inter-Society Networking Panel GRSS/MTT-S/CIS Panel Session: Promoting Connection and Cooperation
https://www.etran.rs/2024/en/home-english/
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
2. 4878 R. Sharma et al.
MNRAS 526, 4877–4884 (2023)
Table 1. Log of AstroSat observation (ID: 9000003922) of SGR J1830−0645.
AstroSat Start time Stop time Mode Obs. span Clean exposure
instrument (yyyy-mm-dd hh:mm:ss) (yyyy-mm-dd hh:mm:ss) (ks) (ks)
SXT 2020-10-16 04:17:32 2020-10-19 02:13:32 PC 251.8 38.8
LAXPC 2020-10-16 03:37:03 2020-10-19 04:44:46 EA 263.2 108.4
variability in temperature throughout the rotation cycle of the pulsar.
The pulse profiles of the two blackbody emission components are
aligned in phase, thereby indicating that the two regions are not
spatially separated (Coti Zelati et al. 2021; Younes et al. 2022b). The
spin modulation pattern observed in the soft X-ray emission is due to
changes in the blackbody emission area of both components. Several
short X-ray bursts have been observed from NICER and Swift (Ray
et al. 2020; Coti Zelati et al. 2021; Younes et al. 2022a). The spectra
of these bursts can be described with either a hot blackbody or a
power-law emission.
For the current work, we have used data from the Soft X-
ray Telescope (SXT) and Large Area X-ray Proportional Counter
(LAXPC) instruments onboard AstroSat (Agrawal 2006; Singh et al.
2014). Section 2 describes the observation details and the data
reduction process. The results from the timing, spectral, and burst
analyses of SGR J1830−0645 are presented in Section 3. Section 4
discusses the implications of our findings.
2 OBSERVATIONS
India’s first multiwavelength astronomical mission, AstroSat, was
launched in 2015 September by the Indian Space Research Organiza-
tion. It comprises five scientific instruments that can simultaneously
observe a source over a wide energy range from optical to hard X-
rays—a scanning sky monitor (Ramadevi et al. 2018), an ultraviolet
imaging telescope (Tandon et al. 2017), SXT (Singh et al. 2017),
LAXPCs (Yadav et al. 2016; Agrawal et al. 2017), and a cadmium
zinc telluride imager (Rao et al. 2017).
The data from an AstroSat observation of SGR J1830−0645
(Observation ID T03 255T01 9000003922) made on 2020 October
16 were analysed for this work (see Table 1 for observation details).
During this observation, SGR J1830−0645 was observed for a span
of ∼260 ks. For the current work, we have used data from SXT and
LAXPC only.
2.1 AstroSat/SXT
AstroSat/SXT is a focusing X-ray telescope that is capable of
performing X-ray imaging and spectroscopy in the 0.3–8 keV energy
range with an energy resolution of ∼150 eV. It consists of a charge-
coupled device (CCD) camera, which is operated in photon counting
(PC) mode with a time resolution of 2.37 s and in fast windowed (FW)
mode with a time resolution of 0.278 s. The on-axis effective area is
∼90 cm2
at 1.5 keV and the FWHM of the point spread function in
the focal plane is ∼2 arcmin (see Singh et al. 2016, 2017 for details).
The SXT data of SGR J1830−0645 were taken in the PC
mode. Level-1 data were processed by using SXTPIPELINE ver-
sion 1.4b, which generated the filtered level-2 cleaned event files.
SXTEVTMERGERTOOL was used to merge the cleaned event files
from different orbits in the SXT data. We used the XSELECT
v2.4m tool to extract the image, light curve, and spectra of SGR
J1830−0645. A circular region of 15 arcmin radius was consid-
ered as a source region around the source location. The ancillary
response file (ARF) was created with the SXTARFMODULE tool
by using the ARF provided by the SXT team. The response file
(sxt pc mat g0to12.rmf) and the blank-sky background spectrum file
(SkyBkg comb EL3p5 Cl Rd16p0 v01.pha) provided by the SXT
team were used.1
2.2 AstroSat/LAXPC
AstroSat/LAXPC consists of three co-aligned proportional counters
(LAXPC10, LAXPC20, and LAXPC30) covering a broad energy
range of 3–80 keV with a total effective area of 6000 cm2
at 15 keV
(Yadav et al. 2016; Agrawal et al. 2017). Every LAXPC detector
has the capability to record the arrival time of photons with a time
resolution of 10 μs. Due to issues related to high background and gain
instability of LAXPC10 and detector LAXPC30 being switched off,
we have only used data from LAXPC20 for the current work. The
energy resolution for LAXPC20 at 30 keV is about 20 per cent (Antia
et al. 2021).
The event analysis mode (EA) data from LAXPC20 were used for
performing the timing and spectral analyses of SGR J1830−0645.
The EA mode data were processed by using the LAXPC software2
(LAXPCSOFT: version 3.4.3). The light curves and spectra for the
source and background were extracted from level-1 files by using
the tool LAXPCL1. The background in the LAXPC is estimated from
the blank-sky observations (for details, see Antia et al. 2017). To
minimize the background, we have performed all analyses using
the data from the top layer (L1, L2) of the LAXPC20 detector
(Sharma et al. 2020; Sharma, Sanna Beri 2023b). We have used
corresponding response files to obtain channel-to-energy conversion
information while performing energy-resolved analyses.
The AS1BARY3
tool was used to apply barycentric correction to the
photon arrival times in the level-2 files of LAXPC and SXT using the
JPL DE405 ephemeris and source position RA (J2000) = 18h
30m
41.
s
64 and Dec. (J2000) = −06◦
45
16.
9 obtained from Chandra
observations (Gogus, Kouveliotou Younes 2020b; Younes et al.
2022a).
3 ANALYSES AND RESULTS
Fig. 1 shows the evolution of the 0.5–10 keV count rate of
SGR J1830−0645 extracted from the 32 observations made with
Swift/XRT4
(Evans et al. 2007) over a baseline of about 400 d starting
from the onset of the outburst (MJD 59132.6176). The time evolution
of the count rate can be described with an exponential function
(∝ e−t/τ
, shown by the solid red line) with an e-folding time (τ) of
113 ± 4 d (χ2
= 221 for 29 degrees of freedom, dof), which is nearly
double that reported by Coti Zelati et al. (2021) using the first 34 d
of data coverage of SGR J1830−0645.
1https://www.tifr.res.in/∼astrosat sxt/dataanalysis.html
2https://www.tifr.res.in/∼astrosat laxpc/LaxpcSoft.html
3http://astrosat-ssc.iucaa.in/?q = data and analysis
4Created from the online ‘Build XRT products’ tool at the UK Swift Science
Data Centre.
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Figure 1. 0.5–10 keV Swift/XRT light curve of SGR J1830−0645 over a
baseline of ∼400 d since the onset of the outburst (MJD 59132.6176). The
red solid line denotes the best-fitting exponential function with an e-folding
time of 113 ± 4 d. The vertical blue solid lines mark the observation span of
the AstroSat observation.
Figure 2. Top: The 0.9–7 keV AstroSat/SXT light curve of SGR J1830−0645
binned at 2.3775 s. Bottom: The 3–25 keV AstroSat/LAXPC light curve of
SGR J1830−0645 binned at 0.1 s.
3.1 Timing analysis
Fig. 2 shows the SXT (0.9–7 keV) and LAXPC (3–25 keV) light
curves of SGR J1830−0645 binned with 2.3775 and 0.1 s, respec-
tively. Several short bursts lasting a few milliseconds were detected
only with LAXPC during this observation.
We used the χ2
maximization technique to determine the spin
period of SGR J1830−0645. From the literature, the spin period is
known to be ∼10.4157 s. We folded the LAXPC light curve over
a range of periods (10.410—10.420 s) with a resolution of 10−6
s
by using the EFSEARCH tool of the XRONOS subpackage of FTOOLS
(Blackburn et al. 1999). We obtained a spin period of 10.415 730 s
for epoch MJD 59138. We have detected pulsations only up to
10 keV. The error in the spin period was estimated by using the
bootstrap method (Lutovinov, Tsygankov Chernyakova 2012;
Boldin, Tsygankov Lutovinov 2013). We simulated 1000 light
curves by the method described in Sharma, Jain Dutta (2022),
Sharma et al. (2023a) and obtained the spin period for each of
Figure 3. Energy-resolved pulse profile of SGR J1830−0645, generated
from SXT (left) and LAXPC (right). The respective pulsed fraction values
are noted in each panel. Two rotation cycles of the pulsar are shown for clarity.
them by using the epoch-folding technique. We obtained a standard
deviation of 4 × 10−6
s in the best spin period distribution. This
number was taken as the error of the pulse period. From the SXT
data, we found a spin period of 10.415 72(1) s, consistent with the
estimate from the LAXPC data. Using a phase-coherent timing
analysis, we have estimated the limit on the spin period derivative to
be |Ṗ| 2 × 10−10
s s−1
at a 90 per cent confidence limit.
Fig. 3 shows the energy-resolved pulse profiles of SGR
J1830−0645, generated from SXT (in the energy ranges 0.9–3, 3–7,
and 0.9–7 keV) and LAXPC (in the energy ranges 3–6, 6–10, and
3–10 keV), using the spin period derived with LAXPC. The SXT pro-
files show a phase shift of ∼1.4 s relative to LAXPC, also observed
in the pulse profiles reported by Beri et al. (2021). This phase shift
could be instrumental and related to the readout time of the SXT
CCD. The 0.9–3 keV SXT pulse profile displayed an asymmetric
single-peak morphology with a minor peak just before the main
peak. The 3–7 keV SXT profile was also asymmetric but relatively
smoother. The pulsed fraction (defined as the semi-amplitude of the
modulation in the pulse profile divided by the average source count
rate)5
was found to increase from about 30 per cent at 0.9–3 keV
energy to 37 per cent at 3–7 keV. The LAXPC pulse profile displayed
a similar morphology, with a minor peak in the rising part of the
profile at low energies (3–6 keV), which could possibly be attributed
to hotspots on the neutron star surface, while the profile at 6–
10 keV is more complex. Similar features were observed in the pulse
profiles extracted from the XMM–Newton and NICER observations
(Coti Zelati et al. 2021; Younes et al. 2022a). The LAXPC pulsed
fraction was found to decrease from ∼34 per cent (below 6 keV) to
∼20 per cent (at 6–10 keV). Fig. 4 shows the significant evolution
of the pulsed fraction with energy in SGR J1830−0645. It increases
up to energies around 5 keV and shows a steep drop thereafter, a
behaviour also reported by Coti Zelati et al. (2021) and Younes et al.
(2022b).
3.2 Spectral analysis
We have performed a spectral analysis of the persistent-only emission
of SGR J1830−0645. We simultaneously fitted spectra from SXT
5Pulsed fraction = Imax−Imin
Imax+Imin
, where Imax and Imin are the maximum and
minimum intensities of the pulse profile.
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Figure 4. Evolution of the pulsed fraction in SGR J1830−0645 with energy
as seen in the SXT and LAXPC data.
Figure 5. (a) The 0.9–25 keV energy spectrum of SGR J1830−0645 ob-
tained from SXT and LAXPC data. (b) The residuals for a model comprising
continuum emission components without a Gaussian emission line. (c) The
residuals with a best-fitting model comprising two blackbodies and power-law
and Gaussian components.
and LAXPC in the 0.9–25 keV energy range to study the spectral
properties of the source. We have ignored LAXPC20 data above
25 keV because of the large uncertainty in the background estimation
(Antia et al. 2017; Sharma et al. 2023a). We have used XSPEC v12.12.0
from the HEASOFT 6.29 package for spectral fitting (Arnaud 1996).
We used a systematic uncertainty of 1 per cent during spectral fitting
(Antia et al. 2017). The SXT and LAXPC spectra were grouped using
GRPPHA to have a minimum count of 50 counts per bin. A constant
factor of 1 fixed for LAXPC was added for cross-calibration.
Fig. 5 shows the 0.9–25 keV energy spectrum of SGR
J1830−0645, which can be described with a model compris-
ing a double blackbody along with a power-law component
(bbodyrad+bbodyrad+powerlaw) (Coti Zelati et al. 2021).
This model has a χ2
value of 323 for 253 dof. The addition of a
Gaussian feature around 6.4 keV improved the fit (χ2
/dof = 276/250)
with an F-test probability of improvement by chance of about 10−8
,
which corresponds to 5.6σ significance. The parameters of the best-
Table 2. Best-fitting spectral parameters of SGR J1830−0645. All errors
reported in this table are at a 90 per cent confidence level (χ2 = 2.7).
Component Parameter Value
tbabs NH (1022 cm−2) 1.00+0.22
−0.19
bbodyrad kTHot (keV) 1.096+0.05
−0.04
RBB (km)b 0.65+0.06
−0.07
norm 2.66+0.51
−0.56
bbodyrad kTWarm (keV) 0.46+0.09
−0.07
RBB (km)b 2.37+1.25
−0.55
norm 35.1+37.0
−16.4
powerlaw 0.39 ± 0.13
norm (10−4) 1.73+0.8
−0.5
Gaussian Eline (keV) 6.44 ± 0.15
Sigma (keV) 0.26+0.25
−0.24
norm (10−5) 9.7+3.4
−2.6
EQW (keV) 0.24+0.10
−0.09
Factor CSXT 0.91 ± 0.04
FBB-hot
0.9–25 keV 4.06 × 10−11
FBB-warm
0.9–25 keV 1.40 × 10−11
Unabs. fluxa F
powerlaw
0.9−25 keV 3.03 × 10−11
FTotal
0.9–25 keV 8.60 × 10−11
FTotal
0.1–100 keV 3.40 × 10−10
χ2/dof 276.6/250
Notes. aFlux is in units of erg cm−2 s−1.
bAssuming a fiducial distance of 4 kpc (Younes et al. 2022a).
fitting spectral model are given in Table 2. They are consistent with
those of Coti Zelati et al. (2021), except for the emission line.
The inclusion of an emission-line component in the energy
spectrum improved the best-fitting statistics by χ2
of 46.8 for
three additional dof. Although popular amongst the astrophysics
community, the F-test is associated with caveats when it comes
to the detection of emission lines in a spectral model (Protassov
et al. 2002). Therefore, we estimated the significance of the potential
spectral line by using the simftest script from XSPEC. This routine
uses the Monte Carlo method to simulate data sets with the same
counting statistics as the original data. We simulated 10 000 data
sets, which were fitted with the best-fitting spectral models (both with
and without a 6.4 keV emission line). Fig. 6 shows the distribution
of χ2
values obtained from fitting every simulated data set. From
the simftest routine, we obtained a maximum χ2
value of 15,
which is significantly lower than the χ2
value of 46.8 obtained in
the original data. A large deviation of χ2
confirms a significant
detection of the emission line in the spectra. To be doubly sure,
we also tested whether the presence of the spectral line is due
to systematics in the LAXPC instrument. For this, we increased
the systematic error in the spectral fitting to 2 per cent. We found
an improvement of χ2
of 20 for three additional dof; the F-test
probability of finding such a change by chance is ∼3 × 10−4
,
which corresponds to 3.6σ significance. It is important to mention
here that the spectral analysis of observations made with the X-ray
missions XMM–Newton and NuSTAR has not detected the presence
of this spectral line (Coti Zelati et al. 2021). Even a dedicated
NICER monitoring of the source has not shown any evidence of
the presence of emission lines (Younes et al. 2022a). Therefore, even
though we have performed thorough statistical checks that support
the presence of the emission line, it is possible that the 6.4 keV
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Figure 6. Histogram showing the results of the simftest simulations for
testing the detection significance of the emission line. The overlaid solid black
curve represents the χ2 distribution for three dof. The vertical red dashed line
marks the χ2 value obtained from spectral fitting of the real data.
feature observed in our data is an instrumental effect. If our detection
of line emission in the persistent emission of SGR J1830−0645 is
indeed true, then it has several implications for the X-ray emis-
sion mechanism of magnetars, some of which are highlighted in
Section 4.
In order to check the correlation between the emission line and
burst/non-burst phase of SGR J1830−0645, we generated stacked
spectra from 100, 200, 300, 400, and 500 s data before and after each
burst. The spectrum from all the segments showed the presence of
a ∼6.4 keV emission line with a probability of chance improvement
10−4
(i.e. significance 3σ) using simftest, except for the first
100 s segment where we obtained a probability of 0.0029. A relatively
high probability, in this case, could be due to overall low exposure
(∼6.2 ks compared to more than 20 ks for other segments) and thus
poorer statistics. The equivalent width of the emission line during
these segments was similar to that obtained in the average spectrum
of the source (∼0.25–0.30 keV), clearly indicating that the presence
of line is not related to the occurrence of bursts in SGR J1830−0645.
3.3 Burst analysis
In order to quantify the occurrence of X-ray bursts, we used only
the LAXPC data because of the relatively large time resolution
(2.37 s) of SXT. We binned the 3–25 keV LAXPC time series with a
time resolution of 0.01 s. We searched for bursts in every good time
interval (GTI) of the time series by using the find peaks routine
of the SCIPY package (Virtanen et al. 2020).
Using a Poisson distribution, the probability (Pi) of the number of
counts occurring randomly in each time bin (ni) is given by
Pi =
λni e−λ
ni!
. (1)
Here, λ is the local mean count rate of every GTI. The events for
which Pi was less than 10−4
/N were labelled as bursts. Here, N is
the total number of time bins in the respective GTI (Gavriil, Kaspi
Woods 2004; Borghese et al. 2020). Using this algorithm, we have
detected a total of 67 bursts. Fig. 7 shows the profile of the two
brightest bursts observed with LAXPC. The brightest burst had a
peak count of about 100 counts in a 10 ms bin, corresponding to a
fluence of about 419 counts within a duration of 0.09 s.
Fig. 8 shows the 3–25 keV burst spectra that have been modelled
with an absorbed power law (χ2
/dof = 17.9/18) with = 1.52 ± 0.14
Figure 7. The 3–25 keV profile of the two brightest bursts observed with
LAXPC.
Figure 8. The spectra of the two brightest bursts detected during the AstroSat
observation of SGR J1830−0645. The bottom panel shows the residuals with
respect to the best-fitting absorbed power-law model.
where NH was fixed at 1.0 × 1022
cm−2
(Table 3). For both the bursts,
the LAXPC energy spectra could not be modelled with a single
blackbody as reported in the literature (Coti Zelati et al. 2021; Younes
et al. 2022a). For the brightest burst, we obtained an unabsorbed 3–
25 keV flux of 5.41 × 10−8
erg cm−2
s−1
, corresponding to a fluence
of ∼5 × 10−9
erg cm−2
. To date, the Swift/BAT burst detected on 2020
November 5 has the highest reported fluence (∼3.2 × 10−8
erg cm−2
)
at 15–150 keV (Coti Zelati et al. 2021). On extrapolating our results,
we obtained a 15–150 keV fluence of ∼1.1 × 10−8
erg cm−2
. The
cumulative spectrum of all the 67 bursts is also well described with a
power-law ( ∼ 1.7) model having an average 3–25 keV unabsorbed
flux of ∼1 × 10−10
erg cm−2
s−1
. The burst spectra did not show any
evidence of the presence of the ∼6.4 keV emission line.
The left-hand panel of Fig. 9 shows the fluence distribution of all
67 bursts. The 3–25 keV high-fluence tail in this distribution ranges
from (0.2–48) × 10−10
erg cm−2
. This tail can be described by a
power-law function having an index of ∼1.88. From the 0.7–8 keV
NICER data, Younes et al. (2022a) described the high-fluence tail
with a power-law function having an index of 1.5. The right-hand
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Figure 9. Left: The fluence distribution of 3–25 keV bursts detected with AstroSat in SGR J1830−0645. The red dashed line shows the best-fitting power-law
trend (F−1.88). Right: Distribution of the duration (T90) of the X-ray bursts.
Table 3. Spectral parameters of the two brightest bursts detected in SGR
J1830−0645 with LAXPC. The best-fitting model used was the absorbed
power-law.
Component Parameter Burst 1 Burst 2
tbabs NH (1022 cm−2) 1.0fixed
powerlaw 1.52 ± 0.14 1.56 ± 0.38
norm 5.4+1.9
−1.4 1.9+2.4
−1.1
Unabs. flux F3–25 keV (erg cm−2 s−1) 5.41 × 10−8 1.69 × 10−8
Unabs. flux F0.1–100 keV (erg cm−2 s−1) 1.58 × 10−7 4.87 × 10−8
χ2/dof 17.9/18
panel of Fig. 9 shows the distribution of the burst duration (T90
6
).
The average duration of all 67 bursts was about 33 ms with a standard
deviation of 13 ms.
4 DISCUSSION
This work reports results from the timing and spectral analyses of the
AstroSat observation of SGR J1830−0645 made on 2020 October
16 during its first detected outburst. We conclude the following from
our findings.
(i) Detection of 0.9–10 keV pulsations in SGR J1830−0645.
(ii) Pulse period of 10.415 730(4) s at an epoch of MJD 59138.
(iii) Variation in the morphology of the pulse profiles with energy
(pronounced dip just before the main peak at low energies and almost
sinusoidal at higher energies) along with significant variation in the
pulsed fraction.
(iv) The 0.9–25 keV SXT + LAXPC energy spectrum comprising
the sum of two thermal components and a power-law component.
(v) Tentative detection of a 6.4 keV emission line with an equiva-
lent width of about 0.24 keV.
(vi) Detection of several short subsecond X-ray bursts during this
observation of AstroSat.
The pulsed fraction of SGR J1830−0645 shows a significant
evolution with increasing energy. It is observed to increase for
energies up to ∼5 keV and shows a steep drop thereafter. This trend
is different from that observed in several other magnetars, such as
6Time interval between 90 per cent of the peak counts.
1E 1841−045, 1E 2259+586, and 4U 0142+61 (Kuiper et al. 2006;
An et al. 2013; Vogel et al. 2014). Clearly, the pulsed fraction trend
seen in SGR J1830−0645 is in stark contrast to the coronal outflow
model of Beloborodov (2013).
SGR J1830−0645 displays spectral properties typical of most
magnetars in the soft X-ray band (Thompson, Lyutikov Kulkarni
2002; Tiengo, Esposito Mereghetti 2008; Coti Zelati et al.
2018). The energy spectrum consists of two blackbody (thermal)
components along with a non-thermal power law associated with
resonantly up-scattered soft thermal photons as they traverse from the
stellar surface through the magnetosphere (Fernández Thompson
2007; Nobili, Turolla Zane 2008; Coti Zelati et al. 2021). Assuming
a distance of 4 kpc (Younes et al. 2022a), we have estimated the size
of the emitting regions to be RBB of 0.65 km (for kTBB of 1.1 keV)
and RBB of 2.45 km (kTBB of 0.46 keV). During this observation, the
blackbody components carried about 47 per cent (hot component)
and 16 per cent (warmer component) fractions of the total flux.
We detected a total of 67 bursts from the LAXPC data set with an
average duration of 33 ms. The brightest burst lasted for ∼90 ms and
had a fluence of ∼5 × 10−9
erg cm−2
in the 3–25 keV energy range.
The fluence tail of the bursts can be described by a power-law function
of index ∼1.88. The power-law fluence distribution of burst fluence
observed in SGR J1830−0645 is similar to several magnetars (see
e.g. Cheng et al. 1996; Scholz Kaspi 2011; Collazzi et al. 2015) and
is believed to be consistent with either magnetospheric reconnection
or the crust-quake theories of the burst-triggering mechanism (for
example, see Thompson Duncan 1995; Lyutikov 2003).
We have detected the presence of an emission-line-like feature
in SGR J1830−0645. This detection makes SGR J1830−0645 one
of the few magnetars that have shown the presence of emission
lines. In the case of SGR 1900+14, an emission feature at 6.4 keV
accompanied by a faint hint of its harmonic at ∼13 keV was detected
during the first 0.3 s of the precursor of a strong burst (Strohmayer
Ibrahim 2000). In XTE J1810−197, a narrow 12.6 keV emission
feature was reported by Woods et al. (2005) by using RXTE data
during the bright X-ray tail of a burst. In 1E 1048.1−5937, Gavriil,
Kaspi Woods (2002) reported the presence of a ∼14 keV emission
feature during the initial stages of a burst detected with RXTE. For this
magnetar, An et al. (2014) also reported a ∼13 keV emission feature
using NuSTAR data, thereby ruling out any instrumental effects. In
all these magnetars, the emission line is a transient feature observed
occasionally during the burst, but we have found the emission feature
during persistent emission in SGR J1830−0645. We did not find
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evidence for this emission line in the individual spectra of the two
brightest bursts nor in the cumulative burst spectra.
There are several possibilities that could explain the presence
of this emission line but, owing to the lack of sufficient data,
these possibilities come with many limitations. It is possible that
the emission line is a result of the fluorescence of iron due to
the presence of relatively cool material near the neutron star. We
have detected an emission line with an equivalent width of about
∼0.24 keV. This is similar to the emission line generally observed
in accreting X-ray pulsars (e.g. Naik, Paul Ali 2011; Naik Paul
2012; Sharma et al. 2023a). Another possibility for the presence of
the emission line is related to proton and alpha-particle cyclotron
transitions in astrophysical systems with ultrastrong magnetic fields
(Strohmayer Ibrahim 2000; Ibrahim et al. 2002, 2007). For
magnetars having B ࣠ 1014
G, the electron cyclotron absorption line
energy is O(MeV), which is out of bounds for AstroSat detectors.
The proton and alpha-particle cyclotron resonances are well within
reach, with fundamentals at Ep = 6.3(1 + z)−1
(B/1015
G) keV and
Eα = 3.2(1 + z)−1
(B/1015
G) keV, respectively. Using (1 + z) = 1.31
for a canonical neutron star of M = 1.4M and R = 10 km, the surface
field strength in SGR J1830−0645 comes out to be ∼1.3 × 1015
G for
proton cyclotron resonances, which is slightly higher than the dipole
magnetic field strength derived from the spin-down measurements
by Younes et al. (2022a) and Coti Zelati et al. (2021).
In spite of these possibilities and owing to the fact that the emission
line has not been detected with other X-ray missions (Coti Zelati
et al. 2021; Younes et al. 2022a), it is possible that its presence in
the AstroSat observation is an instrumental systematic effect. Thus,
more data and intensive analysis are required before commenting on
its viability.
ACKNOWLEDGEMENTS
This work has made use of data from the AstroSat mission of
the Indian Space Research Organisation (ISRO), archived at the
Indian Space Science Data Centre (ISSDC). We thank the LAXPC
Payload Operation Center (POC) and SXT POC at TIFR, Mumbai
for verifying and releasing the data via the ISSDC data archive
and providing the necessary software tools. We have also made
use of the software provided by the High Energy Astrophysics
Science Archive Research Center (HEASARC), which is a service
of the Astrophysics Science Division at NASA/GSFC. This work
has also made use of data supplied by the UK Swift Science Data
Centre at the University of Leicester. This paper makes use of the
following software packages: NUMPY (Harris et al. 2020), SCIPY
(Virtanen et al. 2020), ASTROPY (Astropy Collaboration 2018), and
MATPLOTLIB (Hunter 2007). We thank the anonymous referee for
insightful comments and suggestions, which helped to improve the
manuscript significantly.
DATA AVAILABILITY
Data used in this work can be accessed through the Indian Space
Science Data Center (ISSDC) at https://astrobrowse.issdc.gov.in/ast
ro archive/archive/Home.jsp.
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