1) The Chandra X-ray Observatory was used to observe the supermassive black hole at the center of the Milky Way, Sgr A*, for a total of 3 megaseconds.
2) The observations revealed extended X-ray emission around Sgr A* that aligns spatially with a surrounding disk of massive stars.
3) Spectral analysis ruled out low-mass stars as the origin of the X-ray emission and instead found evidence that the emission is from a radiatively inefficient accretion flow onto the black hole, with an outflow present.
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
Serendipitous discovery of an extended xray jet without a radio counterpart i...Sérgio Sacani
A recent Chandra observation of the nearby galaxy cluster Abell 585 has led to the discovery of
an extended X-ray jet associated with the high-redshift background quasar B3 0727+409, a luminous
radio source at redshift z = 2:5. This is one of only few examples of high-redshift X-ray jets known
to date. It has a clear extension of about 1200, corresponding to a projected length of 100 kpc, with
a possible hot spot located 3500 from the quasar. The archival high resolution VLA maps surprisingly
reveal no extended jet emission, except for one knot about 1:400 from the quasar. The high X-ray to
radio luminosity ratio for this source appears consistent with the / (1 + z)4 amplication expected
from the inverse Compton radiative model. This serendipitous discovery may signal the existence
of an entire population of similar systems with bright X-ray and faint radio jets at high redshift, a
selection bias which must be accounted for when drawing any conclusions about the redshift evolution
of jet properties and indeed about the cosmological evolution of supermassive black holes and active
galactic nuclei in general.
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
PROBING FOR EVIDENCE OF PLUMES ON EUROPA WITH HST/STISSérgio Sacani
Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude
region on Europa – spectroscopic detection of off-limb line emission from the dissociation
products of water. Here, we present Hubble Space Telescope (HST) direct images of Europa in
the far ultraviolet (FUV) as it transited the smooth face of Jupiter, in order to measure absorption
from gas or aerosols beyond the Europa limb. Out of ten observations we found three in which
plume activity could be implicated. Two show statistically significant features at latitudes similar
to Roth et al., and the third, at a more equatorial location. We consider potential systematic
effects that might influence the statistical analysis and create artifacts, and are unable to find any
that can definitively explain the features, although there are reasons to be cautious. If the
apparent absorption features are real, the magnitude of implied outgassing is similar to that of the
Roth et al. feature, however the apparent activity appears more frequently in our data.
The document summarizes research from images taken by the New Horizons spacecraft of Charon, Pluto's largest moon. The images reveal Charon has a reddish polar cap at its north pole. Thermal models show the pole experiences long periods of extreme cold temperatures due to Charon's high obliquity and long seasons. The researchers hypothesize that methane and other volatiles escaping from Pluto's atmosphere become cold-trapped at Charon's winter pole, where they are processed by radiation into non-volatile organic compounds that remain on the surface to form the red cap. Spectral and compositional evidence supports this mechanism of seasonal accumulation of photolyzed volatiles to explain Charon's unique polar color
Wind from the_black_hole_accretion_disk_driving_a_molecular_outflow_in_an_act...Sérgio Sacani
Artigo descreve estudo inédito que mostra que os ventos gerados pelos buracos negros nos centros das galáxias pode acabar com o processo de formação de estrelas nas galáxias hospedeiras.
1) Researchers observed 15 transits of the exoplanet GJ 1214b using the Hubble Space Telescope to measure its transmission spectrum from 1.1 to 1.7 microns.
2) The transmission spectrum was featureless, inconsistent with cloud-free atmospheres dominated by water, methane, carbon monoxide, nitrogen, or carbon dioxide.
3) The most likely explanation for the featureless spectrum is the presence of high-altitude clouds in the planet's atmosphere, which block the transmission of stellar light through the lower atmosphere.
Serendipitous discovery of an extended xray jet without a radio counterpart i...Sérgio Sacani
A recent Chandra observation of the nearby galaxy cluster Abell 585 has led to the discovery of
an extended X-ray jet associated with the high-redshift background quasar B3 0727+409, a luminous
radio source at redshift z = 2:5. This is one of only few examples of high-redshift X-ray jets known
to date. It has a clear extension of about 1200, corresponding to a projected length of 100 kpc, with
a possible hot spot located 3500 from the quasar. The archival high resolution VLA maps surprisingly
reveal no extended jet emission, except for one knot about 1:400 from the quasar. The high X-ray to
radio luminosity ratio for this source appears consistent with the / (1 + z)4 amplication expected
from the inverse Compton radiative model. This serendipitous discovery may signal the existence
of an entire population of similar systems with bright X-ray and faint radio jets at high redshift, a
selection bias which must be accounted for when drawing any conclusions about the redshift evolution
of jet properties and indeed about the cosmological evolution of supermassive black holes and active
galactic nuclei in general.
A highly magnetized twin-jet base pinpoints a supermassive black holeSérgio Sacani
Supermassive black holes (SMBH) are essential for the production of jets in radio-loud active galactic nuclei (AGN). Theoretical
models based on (Blandford & Znajek 1977, MNRAS, 179, 433) extract the rotational energy from a Kerr black hole, which could
be the case for NGC1052, to launch these jets. This requires magnetic fields on the order of 103 G to 104 G. We imaged the vicinity
of the SMBH of the AGN NGC1052 with the Global Millimetre VLBI Array and found a bright and compact central feature that is
smaller than 1.9 light days (100 Schwarzschild radii) in radius. Interpreting this as a blend of the unresolved jet bases, we derive the
magnetic field at 1 Schwarzschild radius to lie between 200 G and 8:3 104 G consistent with Blandford & Znajek models.
This document summarizes research on determining temperatures, luminosities, and masses of the coldest known brown dwarfs. The key findings are:
1) Precise distances were measured for a sample of late-T and Y dwarfs using Spitzer Space Telescope astrometry, allowing accurate calculation of absolute fluxes, luminosities, and temperatures.
2) Y0 dwarfs were found to have temperatures of 400-450 K, significantly warmer than previous estimates, and masses of 5-20 times Jupiter's mass.
3) While having similar temperatures, Y dwarfs showed diverse spectral energy distributions, suggesting temperature alone does not determine spectra. Physical properties like gravity, clouds and chemistry also influence spectra.
PROBING FOR EVIDENCE OF PLUMES ON EUROPA WITH HST/STISSérgio Sacani
Roth et al. (2014a) reported evidence for plumes of water venting from a southern high latitude
region on Europa – spectroscopic detection of off-limb line emission from the dissociation
products of water. Here, we present Hubble Space Telescope (HST) direct images of Europa in
the far ultraviolet (FUV) as it transited the smooth face of Jupiter, in order to measure absorption
from gas or aerosols beyond the Europa limb. Out of ten observations we found three in which
plume activity could be implicated. Two show statistically significant features at latitudes similar
to Roth et al., and the third, at a more equatorial location. We consider potential systematic
effects that might influence the statistical analysis and create artifacts, and are unable to find any
that can definitively explain the features, although there are reasons to be cautious. If the
apparent absorption features are real, the magnitude of implied outgassing is similar to that of the
Roth et al. feature, however the apparent activity appears more frequently in our data.
The document summarizes research from images taken by the New Horizons spacecraft of Charon, Pluto's largest moon. The images reveal Charon has a reddish polar cap at its north pole. Thermal models show the pole experiences long periods of extreme cold temperatures due to Charon's high obliquity and long seasons. The researchers hypothesize that methane and other volatiles escaping from Pluto's atmosphere become cold-trapped at Charon's winter pole, where they are processed by radiation into non-volatile organic compounds that remain on the surface to form the red cap. Spectral and compositional evidence supports this mechanism of seasonal accumulation of photolyzed volatiles to explain Charon's unique polar color
Wind from the_black_hole_accretion_disk_driving_a_molecular_outflow_in_an_act...Sérgio Sacani
Artigo descreve estudo inédito que mostra que os ventos gerados pelos buracos negros nos centros das galáxias pode acabar com o processo de formação de estrelas nas galáxias hospedeiras.
1) The document reports on phase-resolved emission spectroscopy observations of the exoplanet WASP-43b using the Hubble Space Telescope.
2) The observations tracked the planet over three full orbits and measured its thermal emission as a function of orbital phase, allowing the researchers to construct a map of the planet's atmospheric thermal structure.
3) The results found large day-night temperature variations at all measured altitudes, with temperature monotonically decreasing with increasing pressure. A low Bond albedo of 0.07-0.18 and offset of the hottest point from the substellar point were also derived.
Using observations from the Very Large Telescope, astronomers have discovered a dense gas cloud approximately three times the mass of Earth that is falling towards the supermassive black hole at the center of the Milky Way. The cloud is on a highly eccentric orbit that will bring it as close as 3,100 times the event horizon of the black hole in 2013. Over the past three years, the cloud has begun to disrupt due to tidal shearing from the black hole's gravitational forces, and its dynamic evolution over the next few years will provide insights into the black hole's accretion processes.
The open cluster_ngc6520_and_the_nearby_dark_molecular_cloud_barnard_86Sérgio Sacani
This document presents optical photometry and CO observations of the open cluster NGC 6520 and nearby dark molecular cloud Barnard 86. Analysis of the optical data finds the cluster radius is 1.0±0.5 arcmin, smaller than previous estimates. The cluster age is estimated to be 150±50 Myr with reddening of EB−V =0.42±0.10. The distance from the Sun is estimated to be 1900±100 pc, larger than previous estimates. CO observations are used to derive basic properties of Barnard 86 under the assumption it lies at the same distance as the cluster.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
A close pair_binary_in_a_distant_triple_supermassive_black_hole_systemSérgio Sacani
This document reports the discovery of a triple supermassive black hole system through radio observations. Very Long Baseline Interferometry observations revealed two flat-spectrum radio cores, labelled J1502SE and J1502SW, within the galaxy J1502S, separated by about 140 parsecs. Analysis of archival data provides further evidence of this close black hole pair through the detection of 'S-shaped' radio emission between the two cores, indicative of jet precession caused by the binary black holes. This is the closest black hole pair yet discovered and demonstrates a new method for finding binary black holes that cannot be spatially resolved with current instruments.
Towards the identification of the primary particle nature by the radiodetecti...Ahmed Ammar Rebai PhD
To contact the author use ahmed.rebai2@gmail.com
Radio signal from extensive air showers EAS studied by the CODALEMA experiment have been detected by means of the classic short fat antennas array working in a slave trigger mode by a particle scintillator array. It is shown that the radio shower wavefront is curved with respect to the plane wavefront hypothesis. Then a new fitting model (parabolic model) is proposed to fit the radio signal time delay distributions in an event-by-event basis. This model take into account this wavefront property and several shower geometry parameters such as: the existence of an apparent localised radio-emission source located at a distance Rc from the antenna array of and the
radio shower core on the ground. Comparison of the outputs from this model and other reconstruction models used in the same experiment show: 1)- That the radio shower core is shifted from the particle shower core in a statistic analysis approach. 2)- The capability of the radiodetection method to reconstruct the curvature radius
with a statistical error less than 50 g.cm−2 . Finally a preliminary study of the primary particle nature has been performed based on a comparison between data and Xmax distribution from Aires Monte-Carlo simulations for the same set of events.
This document summarizes new results from a study of proper motions in the optical jet of the galaxy M87 using over 13 years of Hubble Space Telescope imaging data. Key findings include:
1) Superluminal velocities (above the speed of light) were measured for knots as far out as knot C in the jet, suggesting these speeds persist over large distances.
2) Significant apparent accelerations both parallel and transverse to the jet axis were found, as well as evidence for stationary features in some knots.
3) Complex motions including differing velocities between nearby features and changes in velocity over time were observed throughout the jet, placing constraints on theoretical jet models.
This document summarizes cosmological parameters measured from galaxy surveys. It discusses:
1) Direct measurements of the Hubble constant from the Hubble Space Telescope and Planck, finding values of 72-74 km/s/Mpc and 67.3 km/s/Mpc respectively.
2) Supernova surveys finding evidence for an accelerating universe with matter density of ~30% and dark energy density of ~70%.
3) Measurements of cosmic microwave background from COBE, WMAP and Planck, determining ages and densities of the universe.
4) Galaxy clustering surveys like SDSS detecting baryon acoustic oscillations to measure dark energy properties.
Mapping spiral structure on the far side of the Milky WaySérgio Sacani
Little is known about the portion of the Milky Way lying beyond the Galactic center at distances
of more than 9 kiloparsec from the Sun. These regions are opaque at optical wavelengths
because of absorption by interstellar dust, and distances are very large and hard to measure.
We report a direct trigonometric parallax distance of 20:4þ2:8
2:2 kiloparsec obtained with the Very
Long Baseline Array to a water maser source in a region of active star formation. These
measurements allow us to shed light on Galactic spiral structure by locating the ScutumCentaurus
spiral arm as it passes through the far side of the Milky Way and to validate a
kinematic method for determining distances in this region on the basis of transverse motions.
Probing the jet_base_of_blazar_pks1830211_from_the_chromatic_variability_of_i...Sérgio Sacani
This document summarizes ALMA observations of the blazar PKS 1830-211 taken over multiple epochs in 2012. The blazar is lensed by a foreground galaxy, producing two resolved images (NE and SW) separated by 1". The observations were taken at frequencies corresponding to 350-1050 GHz in the blazar rest frame. Analysis of the flux ratio between the two images over time and frequency revealed a remarkable frequency-dependent behavior, implying a "chromatic structure" in the blazar jet. This is interpreted as evidence for a "core-shift effect" caused by plasmon ejection very near the base of the jet. The observations provide a unique probe of activity in the region where plasma acceleration occurs in blazar
The shape of Fe Ka line emitted from relativistic accretion disc around AGN b...Milan Milošević
The document discusses simulations of the Fe Kα emission line from accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGN). Ray tracing simulations in Kerr spacetime were used to model the line profiles for different black hole spins, disk radii, inclinations, and emissivity profiles. Relativistic effects like Doppler shifts and gravitational redshift distort the line profiles. Comparisons of simulated and observed line profiles can determine SMBH properties like mass and spin, providing insights into plasma physics and strong gravity near AGN black holes.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
Observed glacier and volatile distribution on Pluto from atmosphere–topograph...Sérgio Sacani
Pluto has a variety of surface frosts and landforms as well as a
complex atmosphere1. There is ongoing geological activity related
to the massive Sputnik Planum glacier, mostly made of nitrogen (N2)
ice mixed with solid carbon monoxide and methane2, covering the
4-kilometre-deep, 1,000-kilometre-wide basin of Sputnik Planum1,3
near the anti-Charon point. The glacier has been suggested to arise
from a source region connected to the deep interior, or from a sink
collecting the volatiles released planetwide1. Thin deposits of N2
frost, however, were also detected at mid-northern latitudes and
methane ice was observed to cover most of Pluto except for the
darker, frost-free equatorial regions2. Here we report numerical
simulations of the evolution of N2, methane and carbon monoxide
on Pluto over thousands of years. The model predicts N2 ice
accumulation in the deepest low-latitude basin and the threefold
increase in atmospheric pressure that has been observed to occur
since 19884–6. This points to atmospheric–topographic processes as
the origin of Sputnik Planum’s N2 glacier. The same simulations also
reproduce the observed quantities of volatiles in the atmosphere and
show frosts of methane, and sometimes N2, that seasonally cover the
mid- and high latitudes, explaining the bright northern polar cap
reported in the 1990s7,8 and the observed ice distribution in 20152.
The model also predicts that most of these seasonal frosts should
disappear in the next decade.
- The document discusses going beyond the standard model of cosmology which assumes a flat Lambda Cold Dark Matter (LCDM) universe with a power-law primordial spectrum.
- It suggests that the universe could be more complicated and that extensions to the standard model need to be properly investigated using advanced statistical methods and high quality observational data.
- Examples of possible extensions discussed include allowing the primordial power spectrum to take on different forms beyond a simple power law, or exploring the possibility that dark energy is not a cosmological constant.
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
This document summarizes research using pulsar timing array data to search for gravitational waves from binary supermassive black holes. The authors analyzed 11 years of timing data for 4 millisecond pulsars and placed an upper limit on the characteristic strain amplitude of the gravitational wave background of Ac,yr < 1.0×10-15 at 95% confidence. This limit is inconsistent with current models of binary supermassive black hole evolution and gravitational wave emission. It suggests binary evolution may be more efficient than assumed or the gravitational wave background is weaker than predicted. Improved pulsar timing data could help distinguish between possible explanations for the non-detection.
Galaxy Cluster Gas Motions with X-ray Surveyor: Probing the Small ScalesJohn ZuHone
This document discusses using X-ray telescopes to study gas motions in galaxy clusters. It argues that while Astro-H will provide some insights into cluster gas kinematics on large scales, an X-ray Surveyor telescope with higher spatial resolution (<1") and effective area would allow researchers to probe gas motions on smaller scales, such as measuring the dissipation scale in the Coma Cluster and precisely characterizing velocity fields in sloshing cores.
Towards the identification of the primary particle nature by the radiodetecti...Ahmed Ammar Rebai PhD
This document summarizes a study using the CODALEMA experiment to analyze radio signals from air showers and identify properties of primary cosmic ray particles. It describes:
1) Analyzing time delays of radio signals compared to a plane wavefront hypothesis and finding systematic deviations, indicating the wavefront is curved.
2) Developing a model to reconstruct the emission center position based on fitting time delays to a parabolic function dependent on curvature radius and antenna distances.
3) Applying the model to 450 selected CODALEMA events and comparing reconstructed shower core positions to results from other models, finding consistency.
1) The Tunable Laser Spectrometer on the Curiosity rover measured methane in the Martian atmosphere on six occasions and found no detection of methane, with an upper limit of 1.3 parts per billion.
2) This contradicts previous orbital and ground-based observations over the last decade that reported detectable methane plumes containing tens of parts per billion of methane.
3) The low measured methane level is not consistent with calculations of methane dispersal from previous large plume detections and suggests methane is being destroyed more rapidly than can be explained by current models.
Human and natural_influences_on_the_changing_thermal_structure_of_the_atmosphereSérgio Sacani
This document analyzes human and natural influences on changing atmospheric temperature patterns based on climate model simulations and satellite observations. The key findings are:
1) Both climate model simulations including human factors and satellite data show widespread tropospheric warming and stratospheric cooling over the past several decades.
2) These temperature changes are unlikely to be due to internal variability or natural external factors alone, based on comparisons to model runs with only natural forcings.
3) The observed temperature pattern matches that expected from increased greenhouse gases more closely than patterns from alternative forcings, providing evidence of a human influence on atmospheric temperatures.
1) The document reports on phase-resolved emission spectroscopy observations of the exoplanet WASP-43b using the Hubble Space Telescope.
2) The observations tracked the planet over three full orbits and measured its thermal emission as a function of orbital phase, allowing the researchers to construct a map of the planet's atmospheric thermal structure.
3) The results found large day-night temperature variations at all measured altitudes, with temperature monotonically decreasing with increasing pressure. A low Bond albedo of 0.07-0.18 and offset of the hottest point from the substellar point were also derived.
Using observations from the Very Large Telescope, astronomers have discovered a dense gas cloud approximately three times the mass of Earth that is falling towards the supermassive black hole at the center of the Milky Way. The cloud is on a highly eccentric orbit that will bring it as close as 3,100 times the event horizon of the black hole in 2013. Over the past three years, the cloud has begun to disrupt due to tidal shearing from the black hole's gravitational forces, and its dynamic evolution over the next few years will provide insights into the black hole's accretion processes.
The open cluster_ngc6520_and_the_nearby_dark_molecular_cloud_barnard_86Sérgio Sacani
This document presents optical photometry and CO observations of the open cluster NGC 6520 and nearby dark molecular cloud Barnard 86. Analysis of the optical data finds the cluster radius is 1.0±0.5 arcmin, smaller than previous estimates. The cluster age is estimated to be 150±50 Myr with reddening of EB−V =0.42±0.10. The distance from the Sun is estimated to be 1900±100 pc, larger than previous estimates. CO observations are used to derive basic properties of Barnard 86 under the assumption it lies at the same distance as the cluster.
Too much pasta_for_pulsars_to_spin_downSérgio Sacani
This document summarizes a study investigating why no isolated X-ray pulsars have been observed with spin periods longer than 12 seconds. The researchers suggest this is due to a highly resistive layer in the inner crust of neutron stars, which is expected to be in a state called "nuclear pasta". Nuclear pasta has an irregular structure that increases electrical resistivity, limiting the spin-down of pulsars. Modeling the long-term magnetic field evolution incorporating a resistive nuclear pasta layer successfully reproduced the observed 12 second period limit. The results provide the first potential observational evidence for the existence of nuclear pasta in neutron star crusts.
A close pair_binary_in_a_distant_triple_supermassive_black_hole_systemSérgio Sacani
This document reports the discovery of a triple supermassive black hole system through radio observations. Very Long Baseline Interferometry observations revealed two flat-spectrum radio cores, labelled J1502SE and J1502SW, within the galaxy J1502S, separated by about 140 parsecs. Analysis of archival data provides further evidence of this close black hole pair through the detection of 'S-shaped' radio emission between the two cores, indicative of jet precession caused by the binary black holes. This is the closest black hole pair yet discovered and demonstrates a new method for finding binary black holes that cannot be spatially resolved with current instruments.
Towards the identification of the primary particle nature by the radiodetecti...Ahmed Ammar Rebai PhD
To contact the author use ahmed.rebai2@gmail.com
Radio signal from extensive air showers EAS studied by the CODALEMA experiment have been detected by means of the classic short fat antennas array working in a slave trigger mode by a particle scintillator array. It is shown that the radio shower wavefront is curved with respect to the plane wavefront hypothesis. Then a new fitting model (parabolic model) is proposed to fit the radio signal time delay distributions in an event-by-event basis. This model take into account this wavefront property and several shower geometry parameters such as: the existence of an apparent localised radio-emission source located at a distance Rc from the antenna array of and the
radio shower core on the ground. Comparison of the outputs from this model and other reconstruction models used in the same experiment show: 1)- That the radio shower core is shifted from the particle shower core in a statistic analysis approach. 2)- The capability of the radiodetection method to reconstruct the curvature radius
with a statistical error less than 50 g.cm−2 . Finally a preliminary study of the primary particle nature has been performed based on a comparison between data and Xmax distribution from Aires Monte-Carlo simulations for the same set of events.
This document summarizes new results from a study of proper motions in the optical jet of the galaxy M87 using over 13 years of Hubble Space Telescope imaging data. Key findings include:
1) Superluminal velocities (above the speed of light) were measured for knots as far out as knot C in the jet, suggesting these speeds persist over large distances.
2) Significant apparent accelerations both parallel and transverse to the jet axis were found, as well as evidence for stationary features in some knots.
3) Complex motions including differing velocities between nearby features and changes in velocity over time were observed throughout the jet, placing constraints on theoretical jet models.
This document summarizes cosmological parameters measured from galaxy surveys. It discusses:
1) Direct measurements of the Hubble constant from the Hubble Space Telescope and Planck, finding values of 72-74 km/s/Mpc and 67.3 km/s/Mpc respectively.
2) Supernova surveys finding evidence for an accelerating universe with matter density of ~30% and dark energy density of ~70%.
3) Measurements of cosmic microwave background from COBE, WMAP and Planck, determining ages and densities of the universe.
4) Galaxy clustering surveys like SDSS detecting baryon acoustic oscillations to measure dark energy properties.
Mapping spiral structure on the far side of the Milky WaySérgio Sacani
Little is known about the portion of the Milky Way lying beyond the Galactic center at distances
of more than 9 kiloparsec from the Sun. These regions are opaque at optical wavelengths
because of absorption by interstellar dust, and distances are very large and hard to measure.
We report a direct trigonometric parallax distance of 20:4þ2:8
2:2 kiloparsec obtained with the Very
Long Baseline Array to a water maser source in a region of active star formation. These
measurements allow us to shed light on Galactic spiral structure by locating the ScutumCentaurus
spiral arm as it passes through the far side of the Milky Way and to validate a
kinematic method for determining distances in this region on the basis of transverse motions.
Probing the jet_base_of_blazar_pks1830211_from_the_chromatic_variability_of_i...Sérgio Sacani
This document summarizes ALMA observations of the blazar PKS 1830-211 taken over multiple epochs in 2012. The blazar is lensed by a foreground galaxy, producing two resolved images (NE and SW) separated by 1". The observations were taken at frequencies corresponding to 350-1050 GHz in the blazar rest frame. Analysis of the flux ratio between the two images over time and frequency revealed a remarkable frequency-dependent behavior, implying a "chromatic structure" in the blazar jet. This is interpreted as evidence for a "core-shift effect" caused by plasmon ejection very near the base of the jet. The observations provide a unique probe of activity in the region where plasma acceleration occurs in blazar
The shape of Fe Ka line emitted from relativistic accretion disc around AGN b...Milan Milošević
The document discusses simulations of the Fe Kα emission line from accretion disks around supermassive black holes (SMBHs) in active galactic nuclei (AGN). Ray tracing simulations in Kerr spacetime were used to model the line profiles for different black hole spins, disk radii, inclinations, and emissivity profiles. Relativistic effects like Doppler shifts and gravitational redshift distort the line profiles. Comparisons of simulated and observed line profiles can determine SMBH properties like mass and spin, providing insights into plasma physics and strong gravity near AGN black holes.
Exocometary gas in_th_hd_181327_debris_ringSérgio Sacani
An increasing number of observations have shown that gaseous debris discs are not an
exception. However, until now we only knew of cases around A stars. Here we present the first
detection of 12CO (2-1) disc emission around an F star, HD 181327, obtained with ALMA
observations at 1.3 mm. The continuum and CO emission are resolved into an axisymmetric
disc with ring-like morphology. Using a Markov chain Monte Carlo method coupled with
radiative transfer calculations we study the dust and CO mass distribution. We find the dust is
distributed in a ring with a radius of 86:0 0:4 AU and a radial width of 23:2 1:0 AU. At
this frequency the ring radius is smaller than in the optical, revealing grain size segregation
expected due to radiation pressure. We also report on the detection of low level continuum
emission beyond the main ring out to 200 AU. We model the CO emission in the non-LTE
regime and we find that the CO is co-located with the dust, with a total CO gas mass ranging
between 1:2 10 6 M and 2:9 10 6 M, depending on the gas kinetic temperature and
collisional partners densities. The CO densities and location suggest a secondary origin, i.e.
released from icy planetesimals in the ring. We derive a CO cometary composition that is
consistent with Solar system comets. Due to the low gas densities it is unlikely that the gas is
shaping the dust distribution.
Observed glacier and volatile distribution on Pluto from atmosphere–topograph...Sérgio Sacani
Pluto has a variety of surface frosts and landforms as well as a
complex atmosphere1. There is ongoing geological activity related
to the massive Sputnik Planum glacier, mostly made of nitrogen (N2)
ice mixed with solid carbon monoxide and methane2, covering the
4-kilometre-deep, 1,000-kilometre-wide basin of Sputnik Planum1,3
near the anti-Charon point. The glacier has been suggested to arise
from a source region connected to the deep interior, or from a sink
collecting the volatiles released planetwide1. Thin deposits of N2
frost, however, were also detected at mid-northern latitudes and
methane ice was observed to cover most of Pluto except for the
darker, frost-free equatorial regions2. Here we report numerical
simulations of the evolution of N2, methane and carbon monoxide
on Pluto over thousands of years. The model predicts N2 ice
accumulation in the deepest low-latitude basin and the threefold
increase in atmospheric pressure that has been observed to occur
since 19884–6. This points to atmospheric–topographic processes as
the origin of Sputnik Planum’s N2 glacier. The same simulations also
reproduce the observed quantities of volatiles in the atmosphere and
show frosts of methane, and sometimes N2, that seasonally cover the
mid- and high latitudes, explaining the bright northern polar cap
reported in the 1990s7,8 and the observed ice distribution in 20152.
The model also predicts that most of these seasonal frosts should
disappear in the next decade.
- The document discusses going beyond the standard model of cosmology which assumes a flat Lambda Cold Dark Matter (LCDM) universe with a power-law primordial spectrum.
- It suggests that the universe could be more complicated and that extensions to the standard model need to be properly investigated using advanced statistical methods and high quality observational data.
- Examples of possible extensions discussed include allowing the primordial power spectrum to take on different forms beyond a simple power law, or exploring the possibility that dark energy is not a cosmological constant.
Magnetic interaction of_a_super_cme_with_the_earths_magnetosphere_scenario_fo...Sérgio Sacani
Solar eruptions, known as Coronal Mass Ejections (CMEs), are
frequently observed on our Sun. Recent Kepler observations of super
ares
on G-type stars have implied that so called super-CMEs, possessing kinetic
energies 10 times of the most powerful CME event ever observed on the Sun,
could be produced with a frequency of 1 event per 800-2000 yr on solar-
like slowly rotating stars. We have performed a 3D time-dependent global
magnetohydrodynamic simulation of the magnetic interaction of such a CME
cloud with the Earth's magnetosphere. We calculated the global structure
of the perturbed magnetosphere and derive the latitude of the open-closed
magnetic eld boundary. We also estimated energy
uxes penetrating the
Earth's ionosphere and discuss the consequences of energetic particle
uxes
on biological systems on early Earth.
Inverse Compton cooling limits the brightness temperature of the radiating plasma to a maximum of
1011.5 K. Relativistic boosting can increase its observed value, but apparent brightness temperatures
much in excess of 1013 K are inaccessible using ground-based very long baseline interferometry (VLBI)
at any wavelength. We present observations of the quasar 3C 273, made with the space VLBI mission
RadioAstron on baselines up to 171,000 km, which directly reveal the presence of angular structure as
small as 26 µas (2.7 light months) and brightness temperature in excess of 1013 K. These measurements
challenge our understanding of the non-thermal continuum emission in the vicinity of supermassive
black holes and require a much higher Doppler factor than what is determined from jet apparent
kinematics.
Keywords: galaxies: active — galaxies: jets — radio continuum: galaxies — techniques: interferometric
— quasars: individual (3C 273)
This document summarizes research using pulsar timing array data to search for gravitational waves from binary supermassive black holes. The authors analyzed 11 years of timing data for 4 millisecond pulsars and placed an upper limit on the characteristic strain amplitude of the gravitational wave background of Ac,yr < 1.0×10-15 at 95% confidence. This limit is inconsistent with current models of binary supermassive black hole evolution and gravitational wave emission. It suggests binary evolution may be more efficient than assumed or the gravitational wave background is weaker than predicted. Improved pulsar timing data could help distinguish between possible explanations for the non-detection.
Galaxy Cluster Gas Motions with X-ray Surveyor: Probing the Small ScalesJohn ZuHone
This document discusses using X-ray telescopes to study gas motions in galaxy clusters. It argues that while Astro-H will provide some insights into cluster gas kinematics on large scales, an X-ray Surveyor telescope with higher spatial resolution (<1") and effective area would allow researchers to probe gas motions on smaller scales, such as measuring the dissipation scale in the Coma Cluster and precisely characterizing velocity fields in sloshing cores.
Towards the identification of the primary particle nature by the radiodetecti...Ahmed Ammar Rebai PhD
This document summarizes a study using the CODALEMA experiment to analyze radio signals from air showers and identify properties of primary cosmic ray particles. It describes:
1) Analyzing time delays of radio signals compared to a plane wavefront hypothesis and finding systematic deviations, indicating the wavefront is curved.
2) Developing a model to reconstruct the emission center position based on fitting time delays to a parabolic function dependent on curvature radius and antenna distances.
3) Applying the model to 450 selected CODALEMA events and comparing reconstructed shower core positions to results from other models, finding consistency.
1) The Tunable Laser Spectrometer on the Curiosity rover measured methane in the Martian atmosphere on six occasions and found no detection of methane, with an upper limit of 1.3 parts per billion.
2) This contradicts previous orbital and ground-based observations over the last decade that reported detectable methane plumes containing tens of parts per billion of methane.
3) The low measured methane level is not consistent with calculations of methane dispersal from previous large plume detections and suggests methane is being destroyed more rapidly than can be explained by current models.
Human and natural_influences_on_the_changing_thermal_structure_of_the_atmosphereSérgio Sacani
This document analyzes human and natural influences on changing atmospheric temperature patterns based on climate model simulations and satellite observations. The key findings are:
1) Both climate model simulations including human factors and satellite data show widespread tropospheric warming and stratospheric cooling over the past several decades.
2) These temperature changes are unlikely to be due to internal variability or natural external factors alone, based on comparisons to model runs with only natural forcings.
3) The observed temperature pattern matches that expected from increased greenhouse gases more closely than patterns from alternative forcings, providing evidence of a human influence on atmospheric temperatures.
High precision abundances_of_the_old_solar_twin_insights_on_li_depletion_from...Sérgio Sacani
- The document presents the results of a chemical abundance analysis of the old solar twin star HIP 102152 (8.2 Gyr) and the younger solar twin 18 Sco (2.9 Gyr) using high-resolution UVES spectra.
- Abundances of 21 elements were derived for HIP 102152 with precisions up to 0.004 dex relative to the Sun. The metallicity of HIP 102152 was found to be nearly solar at [Fe/H] = -0.013.
- Elemental abundances as a function of condensation temperature reveal a solar abundance pattern for HIP 102152, unlike most solar twins. Its pattern most closely matches the Sun. The Li abundance
The document is a scientific paper published in 1972 that consists of the same citation repeated multiple times without any other substantive information. In 3 sentences or less, it is difficult to summarize the content and purpose of the document since it only contains a repeated citation without any other details.
Modelling element abundances_in_semi_analytic_models_of_galaxy_formationSérgio Sacani
This document summarizes a new implementation of detailed chemical enrichment modeling in the Munich semi-analytic model of galaxy formation (L-Galaxies). The new implementation tracks the delayed enrichment of 11 heavy elements from stellar winds, supernovae type II, and supernovae type Ia. It considers different supernovae type II yield sets and three supernovae type Ia delay-time distributions. The results are compared to observational data on local star-forming galaxies, Milky Way disc G dwarfs, and local elliptical galaxies. Overall, the best model matches require a power-law supernovae type Ia delay-time distribution, supernovae type II yields accounting for prior mass loss, and some direct ejection
Alignment of th_angular_momentum_vectors_of_planetary_nebulae_in_the_galactic...Sérgio Sacani
This document analyzes the orientations of 130 planetary nebulae (PNe) in the Galactic Bulge to investigate whether there is a preferred alignment. It finds that while the full sample shows a uniform distribution, the bipolar PNe exhibit a non-uniform distribution with a mean orientation along the Galactic plane at a 90 degree position angle, significant at the 0.001 level. This indicates that the orbital planes of binary systems in old stars are oriented perpendicular to the Galactic plane, likely due to strong magnetic fields during star formation that influenced the angular momentum vectors.
The x-ray diffraction analysis of soil samples from Rocknest at Gale Crater on Mars revealed:
1) Crystalline components including plagioclase, olivine, augite, pigeonite, and minor amounts of other phases.
2) 27±14% of the soil was amorphous material, likely containing multiple iron-bearing and volatile phases including possibly hisingerite.
3) The crystalline components are similar to martian basalts and meteorites, while the amorphous component is similar to soils on Earth like those on Mauna Kea, Hawaii.
The ChemCam instrument on the Curiosity rover identified two main soil types on Mars - a fine-grained mafic soil and a coarse-grained felsic soil locally derived. The mafic soil is similar to widespread martian soils and dust, and possesses a ubiquitous hydrogen signature from hydrated amorphous phases. This hydration may account for a significant fraction of hydrogen detected globally on Mars. ChemCam analyses did not reveal water vapor exchange between the soil and atmosphere. The observations provide constraints on the nature and hydration of amorphous phases in the soil.
A rigid and_weathered_ice_shell_on_titanSérgio Sacani
- Saturn's moon Titan likely has a global subsurface ocean beneath an ice shell 50-200 km thick.
- Analysis of gravity and topography data at long wavelengths shows a strong inverse correlation, indicating a rigid ice shell at least 40 km thick.
- A rigid shell is required to support hundreds of meters of surface erosion/deposition as observed, ruling out an actively convecting shell.
- The results suggest Titan's ice shell has undergone substantial erosion over geological timescales, with implications for its internal structure and composition.
Its official voyager_has_left_the_solar_systemSérgio Sacani
1) After 36 years of traveling away from Earth, the Voyager 1 spacecraft may have finally crossed into interstellar space based on new data.
2) In August 2012, Voyager 1 detected a sharp drop in cosmic rays from inside the heliosphere and an increase in cosmic rays from outside, but the magnetic field did not change direction as expected. This led to debate over whether it had truly crossed the boundary.
3) In April 2013, Voyager detected plasma oscillations at a frequency implying a plasma density 80 times higher than inside the heliosphere, suggesting it had crossed into interstellar space in August 2012. While some researchers still disagree, this is now the consensus of the Voyager team.
Swiging between rotation_and_accretion_power_in_a_millisecond_binary_pulsarSérgio Sacani
This document discusses the discovery of a millisecond X-ray pulsar, IGR J18245-2452, located in the globular cluster M28. The pulsar was previously known as the radio millisecond pulsar PSR J1824-2452I. Observations found that the pulsar alternates between accretion-powered and rotation-powered states on timescales of years, providing direct evidence that these two states cycle in recycled pulsars. When accreting, the pulsar shows X-ray pulsations and luminosity characteristic of other accreting millisecond pulsars. When not accreting, it had previously been detected as a radio pulsar. This demonstrates the evolutionary link between low-mass X
Inference of homogeneous_clouds_in_an_exoplanet_atmosphereSérgio Sacani
1) New visible and infrared observations of the exoplanet Kepler-7b were analyzed to determine its atmospheric properties and detect the presence of clouds.
2) The observations found a westward shift in Kepler-7b's optical phase curve and placed upper limits on its thermal emission that remained undetected in Spitzer bandpasses.
3) The data suggests Kepler-7b has optically thick, high-altitude clouds located west of the substellar point, composed possibly of silicates. The clouds help explain Kepler-7b's unusually high geometric albedo and visible flux that cannot be attributed to thermal emission or molecular hydrogen scattering alone.
Mapping the three_dimensional_density_of_the_galactic_bulge_with_vvv_red_clum...Sérgio Sacani
This document summarizes a study that mapped the three-dimensional density distribution of the Galactic bulge using red clump giant stars identified in the VISTA Variables in the Via Lactea (VVV) survey. The authors constructed extinction maps and used the red clump stars to estimate line-of-sight density distributions by deconvolving the intrinsic luminosity function. Assuming an 8-fold mirror symmetry, they used the line-of-sight densities to construct a 3D density map covering the inner (2.2 × 1.4 × 1.1)kpc of the bulge/bar. The resulting density distribution shows a highly elongated bar with an exponential fall off and axis ratios characteristic of a strongly boxy/pe
In situ observations_of_interstellar_plasma_with_voyager_1Sérgio Sacani
Voyager 1 detected electron plasma oscillations beginning in April 2013 at a frequency corresponding to an electron density of 0.08 cm-3. This provides evidence that Voyager 1 has crossed into the nearby interstellar plasma, as the density is much higher than what is expected in the heliosheath. Comparison with radio emissions detected in 1992 suggests Voyager 1 has encountered a smoothly increasing plasma density ramp, as the frequency drift matches what was observed remotely. Estimating the shock propagation speed that would be required to produce the 1992 drift indicates a plausible speed of 40 km/s.
The Curiosity rover analyzed samples of Martian fines from the Rocknest site using its Sample Analysis at Mars (SAM) instrument suite. SAM detected water, sulfur dioxide, carbon dioxide, and oxygen as the major gases released when heating the fines. The water content and release temperature suggest the water is bound in amorphous materials. Much of the carbon dioxide was likely released from the decomposition of fine-grained iron or magnesium carbonates. Elevated levels of deuterium indicate recent interaction with the atmosphere. Several simple organic compounds were detected but are not definitively of Martian origin.
The petrochemistry of_jake_m_a_martian_mugeariteSérgio Sacani
The rock "Jake_M" was the first rock analyzed by Curiosity on Mars. It has a distinct chemical composition compared to other known Martian rocks. Jake_M has a basaltic composition but is alkaline, with over 15% normative nepheline content. Its chemical makeup is similar to terrestrial mugearites, fractionated alkaline rocks found at ocean islands and rifts. This suggests Jake_M formed through extensive fractional crystallization of an alkaline magma at elevated pressure, possibly with water. The discovery of an alkaline rock expands the diversity of known Martian igneous compositions.
Curiosity at gale_crater_characterization_and_analysis_of_the_rocknest_sand_s...Sérgio Sacani
The Rocknest sand shadow analyzed by the Curiosity rover on Mars was similar to coarse-grained ripples analyzed by previous rovers. It consisted of an upper layer of very coarse sand grains armoring the surface, underlain by finer grains. Analysis found the sand was around 55% crystalline material of basaltic composition and 45% amorphous iron-rich glass. This amorphous component contained the volatiles detected and was similar to soils analyzed at other Mars sites, implying the materials were locally derived from similar basaltic sources globally on Mars.
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.
The characterization of_the_gamma_ray_signal_from_the_central_milk_way_a_comp...Sérgio Sacani
This document analyzes the gamma-ray signal from the central Milky Way that is consistent with emission from annihilating dark matter particles. The authors re-examine Fermi data using cuts on an event parameter to improve gamma-ray maps and more easily separate components. They find the GeV excess is robust and well-fit by a 36-51 GeV dark matter particle annihilating to bottom quarks with a cross section of 1-3×10−26 cm3/s. The signal extends over 10 degrees from the Galactic Center and is spherically symmetric, disfavoring explanations from millisecond pulsars or gas interactions.
A rapidly spinning_supermassive_black_hole_at_the_centre_of_ngc1365Sérgio Sacani
1) XMM-Newton and NuSTAR observed the galaxy NGC 1365 simultaneously over 130 ks, detecting broadband X-ray emission from 3-79 keV.
2) The observations revealed variable absorption below 10 keV and prominent broad emission features between 5-7 keV and 10-30 keV, indicative of relativistic reflection from an accretion disk near a spinning supermassive black hole.
3) Time-resolved spectral analysis was able to disentangle the variable absorption component from the relativistic reflection component. Absorption-dominated models without reflection could be ruled out statistically and on physical grounds.
A magnetar-powered X-ray transient as the aftermath of a binary neutron-star ...Sérgio Sacani
Mergers of neutron stars are known to be associated with short γ-ray
bursts1–4
. If the neutron-star equation of state is sufficiently stiff
(that is, the pressure increases sharply as the density increases), at
least some such mergers will leave behind a supramassive or even a
stable neutron star that spins rapidly with a strong magnetic field5–8
(that is, a magnetar). Such a magnetar signature may have been
observed in the form of the X-ray plateau that follows up to half
of observed short γ-ray bursts9,10. However, it has been expected
that some X-ray transients powered by binary neutron-star mergers
may not be associated with a short γ-ray burst11,12. A fast X-ray
transient (CDF-S XT1) was recently found to be associated with a
faint host galaxy, the redshift of which is unknown13. Its X-ray and
host-galaxy properties allow several possible explanations including
a short γ-ray burst seen off-axis, a low-luminosity γ-ray burst at
high redshift, or a tidal disruption event involving an intermediatemass black hole and a white dwarf13. Here we report a second X-ray
transient, CDF-S XT2, that is associated with a galaxy at redshift
z = 0.738 (ref. 14). The measured light curve is fully consistent with
the X-ray transient being powered by a millisecond magnetar. More
intriguingly, CDF-S XT2 lies in the outskirts of its star-forming host
galaxy with a moderate offset from the galaxy centre, as short γ-ray
bursts often do15,16. The estimated event-rate density of similar
X-ray transients, when corrected to the local value, is consistent
with the event-rate density of binary neutron-star mergers that is
robustly inferred from the detection of the gravitational-wave event
GW170817.
The discovery of_lensed_radio_and_x-ray_sources_behind_the_frontier_fields_cl...Sérgio Sacani
We report on high-resolution JVLA and Chandra observations of the Hubble Space Telescope (HST) Frontier Cluster
MACSJ0717.5+3745. MACSJ0717.5+3745 offers the largest contiguous magnified area of any known cluster,
making it a promising target to search for lensed radio and X-ray sources. With the high-resolution 1.0–6.5 GHz
JVLA imaging in A and B configuration, we detect a total of 51 compact radio sources within the area covered by the
HST imaging. Within this sample, we find sevenlensed sources with amplification factors larger than two. None of
these sources are identified as multiply lensed. Based on the radio luminosities, the majority of these sources are
likely star-forming galaxies with star-formation rates (SFRs) of 10–50 M: yr−1 located at 1 1 z 1 2. Two of the
lensed radio sources are also detected in the Chandra image of the cluster. These two sources are likely active galactic
nuclei, given their 2–10 keV X-ray luminosities of ∼1043–44 erg s−1. From the derived radio luminosity function, we
find evidence for an increase in the number density of radio sources at 0.6 z 2.0, compared to a z 0.3 sample.
Our observations indicate that deep radio imaging of lensing clusters can be used to study star-forming galaxies, with
SFRs as low as ∼10Me yr−1, at the peak of cosmic star formation history.
This paper presents a study of the extended X-ray emission in the Seyfert galaxy NGC 4151 using deep Chandra observations. Key findings include:
1) Emission line maps show strong OVII, OVIII, and NeIX line emission extending along the northeast-southwest direction, consistent with an ionization cone.
2) Spectral analysis finds the extended emission is well described by photoionized plasma models, supporting a dominant role for nuclear photoionization.
3) Faint extended emission is also seen perpendicular to the ionization cone, indicating some leakage of nuclear ionizing radiation through warm absorbers rather than being blocked by an obscuring torus.
Forming intracluster gas in a galaxy protocluster at a redshift of 2.16Sérgio Sacani
Galaxy clusters are the most massive gravitationally bound structures in the Universe, comprising thousands of galaxies and
pervaded by a diffuse, hot “intracluster medium” (ICM) that dominates the baryonic content of these systems. The formation
and evolution of the ICM across cosmic time1
is thought to be driven by the continuous accretion of matter from the large-scale
filamentary surroundings and dramatic merger events with other clusters or groups. Until now, however, direct observations of
the intracluster gas have been limited only to mature clusters in the latter three-quarters of the history of the Universe, and we
have been lacking a direct view of the hot, thermalized cluster atmosphere at the epoch when the first massive clusters formed.
Here we report the detection (about 6σ) of the thermal Sunyaev-Zeldovich (SZ) effect2
in the direction of a protocluster. In fact,
the SZ signal reveals the ICM thermal energy in a way that is insensitive to cosmological dimming, making it ideal for tracing
the thermal history of cosmic structures3
. This result indicates the presence of a nascent ICM within the Spiderweb protocluster
at redshift z = 2.156, around 10 billion years ago. The amplitude and morphology of the detected signal show that the SZ
effect from the protocluster is lower than expected from dynamical considerations and comparable with that of lower-redshift
group-scale systems, consistent with expectations for a dynamically active progenitor of a local galaxy cluster.
Detection of an_unindentified_emission_line_in_the_stacked_x_ray_spectrum_of_...Sérgio Sacani
1. Researchers detected a previously unknown emission line in the stacked X-ray spectrum of 73 galaxy clusters observed by XMM-Newton. 2. The line was detected at an energy of 3.55-3.57 keV and was seen independently in subsamples of clusters. 3. The line was also detected in Chandra observations of the Perseus cluster but not in observations of the Virgo cluster. 4. The nature of this line is unclear - it could be a thermal line from an undetected element, or potentially the decay line of a hypothesized dark matter particle called a sterile neutrino. Further observations are needed to determine the origin of the line.
The nustar extragalactic_survey_a_first_sensitive_lookSérgio Sacani
The document summarizes the first ten sources detected by the Nuclear Spectroscopic Telescope Array (NuSTAR) as part of its extragalactic survey. NuSTAR provides the first sensitive census of the cosmic X-ray background source population at energies above 10 keV. The ten sources have a broad range of redshifts and luminosities, with a median redshift of 0.7 and luminosity of 3×10^44 erg/s. Based on broad-band spectroscopy and SED analysis, the dominant population is quasars with luminosities above 10^44 erg/s, of which around 50% are obscured. However, none are Compton thick and the fraction of Compton thick quasars is constrained to
Magnetic support of_the_optical_emission_line_filaments_in_ngc_1275Sérgio Sacani
1) New Hubble Space Telescope observations of the galaxy NGC 1275 reveal thin thread-like structures within its emission line filaments that extend over 6 kpc but are only 70 pc wide.
2) It is concluded that magnetic fields within the threads, in pressure balance with the surrounding hot gas, are stabilizing the filaments and allowing a large mass of cold gas to accumulate without forming stars.
3) The inferred magnetic field strengths of 10-100 microgauss are sufficient to support the filaments against gravity and tidal forces, and would make the filaments magnetically dominated structures similar to molecular clouds in the Milky Way.
The first X-ray look at SMSS J114447.77-430859.3: the most luminous quasar in...Sérgio Sacani
SMSS J114447.77-430859.3 (z = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in
the last ∼ 9 Gyr . In this paper, we report on the eROSITA/Spectrum–Roentgen–Gamma (SRG) observations of the source from
the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift, XMM-Newton, and
NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 overtime-scales of a year and of a few days,respectively.
When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a = 2.2 ± 0.2 and Ecut = 23+26
−5 keV
. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of τ = 2.5 − 5.3 (5.2 − 8) and
kT = 8 − 18 (7.5 − 14) keV , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by
assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile.
The former model results in a black hole mass estimate of the order of 1010 M , slightly higher than prior optical estimates;
meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning
black hole, and a compact (∼ 10 rg ) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly
suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of
magnitude over the period of ∼ 900 d .
A mildly relativistic wide-angle outflow in the neutron-star merger event GW1...Sérgio Sacani
GW170817 was the first gravitational wave detection of a binary
neutron-star merger1
. It was accompanied by radiation across the
electromagnetic spectrum and localized2
to the galaxy NGC 4993
at a distance of 40 megaparsecs. It has been proposed that the
observed γ-ray, X-ray and radio emission is due to an ultrarelativistic
jet launched during the merger, directed away from
our line of sight3–6. The presence of such a jet is predicted from
models that posit neutron-star mergers as the central engines
that drive short hard γ-ray bursts7,8
. Here we report that the radio
light curve of GW170817 has no direct signature of an off-axis
jet afterglow. Although we cannot rule out the existence of a jet
pointing elsewhere, the observed γ-rays could not have originated
from such a jet. Instead, the radio data require a mildly relativistic
wide-angle outflow moving towards us. This outflow could be the
high-velocity tail of the neutron-rich material dynamically ejected
during the merger or a cocoon of material that breaks out when a
jet transfers its energy to the dynamical ejecta. The cocoon model
explains the radio light curve of GW170817 as well as the γ-rays
and X-rays (possibly also ultraviolet and optical emission)9–15, and
is therefore the model most consistent with the observational data.
Cocoons may be a ubiquitous phenomenon produced in neutronstar
mergers, giving rise to a heretofore unidentified population of
radio, ultraviolet, X-ray and γ-ray transients in the local Universe
The document presents observations of the starburst galaxy NGC 253 using near-infrared imaging and spectroscopy as well as mid-infrared spectroscopy. The observations are used to derive physical properties of the starburst such as the star formation rate, stellar population, and evolutionary stage. Evolutionary synthesis modeling is applied to interpret the observations and show that the starburst in NGC 253 is in a late phase, has been ongoing for 20-30 million years, and is consistent with a modified Salpeter initial mass function.
Sdss1133 an unsually_perssitent_transient_in_a_nearby_dwarf_galaxySérgio Sacani
This document summarizes observations of SDSS1133, an unusual transient object offset from the center of a nearby dwarf galaxy. SDSS1133 has been detected in observations spanning 63 years, and exhibits broad emission lines and strong variability. While initially classified as a supernova due to its non-detection in 2005, more recent observations over the past decade show it has rebrightened over a magnitude and displays properties consistent with both an active galactic nucleus and luminous blue variable star eruptions. Its nature remains ambiguous between an extreme example of pre-supernova mass loss or a potential candidate for a recoiling supermassive black hole.
A spectroscopic sample_of_massive_galaxiesSérgio Sacani
This document describes a study of 16 massive galaxies at z ~ 2 selected from the 3D-HST spectroscopic survey based on the detection of a strong 4000 Angstrom break in their spectra. Spectroscopy and imaging from HST/WFC3 are used to determine accurate redshifts, stellar population properties, and structural parameters. The sample significantly increases the number of spectroscopically confirmed evolved galaxies at z ~ 2 with robust size measurements. The analysis populates the mass-size relation and finds it is consistent with local relations but with smaller sizes by a factor of 2-3. A model is presented where the observed size evolution is explained by quenching of increasingly larger star-forming galaxies at a rate set by
Off nuclear star_formation_and_obscured_activity_in_the_luminous_infrared_gal...Sérgio Sacani
The document summarizes observations of the luminous infrared galaxy NGC 2623 from multiple telescopes. Hubble Space Telescope images reveal over 100 bright star clusters in a 3.2 kpc extension south of the galaxy's nucleus, making it one of the richest concentrations of clusters observed. The clusters have ages between 1-100 Myr based on their optical colors. Archival GALEX data show the extension is very bright in far-ultraviolet but less significant at longer wavelengths. Spitzer data detect [Ne V] emission, confirming the presence of an active galactic nucleus. The off-nuclear star formation corresponds to a rate of 0.1-0.2 solar masses per year, while the bulk of the infrared
A 300 parsec-long jet-inflated bubble around a powerful microquasar in the ga...Sérgio Sacani
This document summarizes the discovery of a 300-parsec-long jet-inflated bubble around a powerful microquasar in the galaxy NGC 7793. Chandra X-ray observations revealed an aligned triple X-ray source within the optical nebula S26, consisting of a central core and two hot spots, interpreted as the core of the X-ray binary and where the jets interact with the ambient medium. Spectral analysis found the core has a hard power-law spectrum, while the hot spots have softer thermal plasma emission. The morphology and properties of S26 resemble those of a powerful FRII-type active galaxy, indicating it is powered by collimated jets with mechanical luminosity of ~10^40 er
Radio continum emission_of_35_edge_on_galaxies_observed_with_the_vlaSérgio Sacani
Usando um dos maiores rádio observatórios do mundo, o Very Large Array do National Radio Astronomy, um grupo de astrônomos descobriram que os halos ao redor dos discos das galáxias espirais são muito mais comuns do que se pensava anteriormente.
A equipe, dirigida pela Dra. Judith Irwin, da Universidade de Queens, em Kingston, ON, Canadá, observou 35 galáxias espirais próximas de lado, de 11 a 137 milhões de anos-luz de distância da Terra.
As galáxias espirais, como a nossa própria Via Láctea ou a famosa Galáxia de Andrômeda, possuem uma vasta maioria de suas estrelas, gás, e poeira num disco plano em rotação com braços espirais. A maior parte da luz e das ondas de rádio observadas com telescópios veem de objetos localizados nesse disco.
“Nós sabíamos antes que alguns halos existiam, mas, usando o poder total do VLA atualizado e o poder total de algumas técnicas de processamento de imagens, nós descobrimos que esses halos são muito mais comuns entre as galáxias espirais do que nós pensávamos antes”, explicou a Dra. Irwin.
This document summarizes Edwin Hubble's 1929 paper establishing a relationship between the distance and radial velocity of extragalactic nebulae. Hubble analyzed spectra and distances of 24 nebulae, finding a linear correlation between higher distances and velocities after correcting for solar motion. Hubble proposed a new solution where velocity varies directly with distance, with a velocity increase of around 500 km/sec per million parsecs. This relationship was supported by data from 22 additional nebulae. The findings helped establish the expanding universe model and Hubble's law relating galaxy recession velocity and distance.
A massive protocluster of galaxies at a redshift of z<5.3Sérgio Sacani
This document describes the discovery of a massive protocluster of galaxies located approximately 1 billion years after the Big Bang (redshift of z=5.3). The protocluster contains overdense regions of massive galaxies extending over 13 megaparsecs. It contains an extremely luminous starburst galaxy with large molecular gas reserves and a luminous quasar. Together, these objects place a minimum total mass of over 4×1011 solar masses in this early cluster, consistent with cosmological simulations of the earliest galaxy clusters. This discovery provides evidence for the hierarchical formation of massive structures in the early universe.
Similar to Dissecting x ray_emitting_gas_around_the_center_of_our_galaxy (20)
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
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.
Removing Uninteresting Bytes in Software FuzzingAftab Hussain
Imagine a world where software fuzzing, the process of mutating bytes in test seeds to uncover hidden and erroneous program behaviors, becomes faster and more effective. A lot depends on the initial seeds, which can significantly dictate the trajectory of a fuzzing campaign, particularly in terms of how long it takes to uncover interesting behaviour in your code. We introduce DIAR, a technique designed to speedup fuzzing campaigns by pinpointing and eliminating those uninteresting bytes in the seeds. Picture this: instead of wasting valuable resources on meaningless mutations in large, bloated seeds, DIAR removes the unnecessary bytes, streamlining the entire process.
In this work, we equipped AFL, a popular fuzzer, with DIAR and examined two critical Linux libraries -- Libxml's xmllint, a tool for parsing xml documents, and Binutil's readelf, an essential debugging and security analysis command-line tool used to display detailed information about ELF (Executable and Linkable Format). Our preliminary results show that AFL+DIAR does not only discover new paths more quickly but also achieves higher coverage overall. This work thus showcases how starting with lean and optimized seeds can lead to faster, more comprehensive fuzzing campaigns -- and DIAR helps you find such seeds.
- These are slides of the talk given at IEEE International Conference on Software Testing Verification and Validation Workshop, ICSTW 2022.
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Dissecting x ray_emitting_gas_around_the_center_of_our_galaxy
1. Dissecting X-ray-emitting Gas around the Center of our Galaxy
Q. D. Wang,1,2∗
M. A. Nowak3
, S. B. Markoff4
, F. K. Baganoff3
,
S. Nayakshin5
, F. Yuan6
, J. Cuadra7
, J. Davis3
, J. Dexter8
,
A. C. Fabian1
, N. Grosso9
, D. Haggard10
, J. Houck3
, L. Ji11
, Z. Li12
,
J. Neilsen13,3
, D. Porquet9
, F. Ripple2
, R. V. Shcherbakov14
1Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK.
2Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA.
3Kavli Institute for Astrophysics and Space Research, MIT, Cambridge MA 02139, USA.
4Astronomical Institute, “Anton Pannekoek”, University of Amsterdam,
Postbus 94249, 1090 GE, Amsterdam, The Netherlands.
5Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK.
6Shanghai Astronomical Observatory, CAS, 80 Nandan Road, Shanghai 200030, China
7 Instituto de Astrofsica, Pontificia Universidad Catlica de Chile, Chile.
8Theoretical Astrophysics Center and Department of Astronomy,
University of California, Berkeley, CA 94720-3411, USA
9Observatoire Astronomique de Strasbourg, Universit´e de Strasbourg,
CNRS, UMR 7550, Strasbourg, France
10CIERA Fellow, Center for Interdisciplinary Exploration and Research in Astrophysics,
Department of Physics and Astronomy, Northwestern University, Evanston, IL USA
11Purple Mountain Observatory, CAS, Nanjing, 210008, P.R. China.
12School of Astronomy and Space Science, Nanjing University, Nanjing, 210093, China.
13Einstein Fellow, Boston University, Boston, MA 02215, USA.
14Hubble Fellow; Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA.
∗To whom correspondence should be addressed; E-mail: wqd@astro.umass.edu.
Most supermassive black holes (SMBHs) are accreting at very low levels and are diffi-
cult to distinguish from the galaxy centers where they reside. Our own Galaxy’s SMBH
provides a uniquely instructive exception, and we present a close-up view of its quies-
cent X-ray emission based on 3 mega-second of Chandra observations. Although the
X-ray emission is elongated and aligns well with a surrounding disk of massive stars,
1
arXiv:1307.5845v1[astro-ph.HE]22Jul2013
2. we can rule out a concentration of low-mass coronally active stars as the origin of the
emission based on the lack of predicted Fe Kα emission. The extremely weak H-like
Fe Kα line further suggests the presence of an outflow from the accretion flow onto
the SMBH. These results provide important constraints for models of the prevalent
radiatively inefficient accretion state.
The nucleus of our Galaxy offers a multitude of unique opportunities for observing the interplay
between a SMBH and its immediate surroundings. The SMBH, named Sgr A*, has a mass of 4.1 ×
106M (1,2), and at its distance of 8 kpc (1), an arcsecond (1 ) subtends 1.2 × 1017 cm, or 1.0 × 105rs,
where rs = 1.2 × 1012 cm is the Schwarzschild radius. The X-ray emission of Sgr A* typically has
an unabsorbed 2-10 keV luminosity (Lx) of a few times 1033 erg s−1 (3), or a factor of ∼ 1011 lower
than the canonical maximum allowed (Eddington) luminosity of the SMBH, representing a common
“inactive” state of galactic nuclei in the Local Universe. Because of its proximity, Sgr A* allows us to
study this extremely low-LX state in unparalleled detail [e.g., (4,5)].
It is believed that Sgr A* feeds off the winds from surrounding massive stars (6–8). At the so-called
Bondi capture radius rB ∼ 4 (Ta/107 K)−1 (9), the gravitational pull of the SMBH wins over the
expanding motion of the medium with effective temperature Ta. The corresponding Bondi capture rate is
estimated to be ˙MB ∼ 1×10−5M yr−1 [e.g., (3)]. If Sgr A* indeed accretes at this rate and if the 10%
X-ray emission efficiency of a “normal” active galactic nucleus applies, one would predict a luminosity
of Lx ∼ 1041 erg s−1. That the observed Lx is nearly a factor of ∼ 108 smaller has led to a renaissance
of radiatively inefficient accretion flow (RIAF) models (10,11), including self-similar solutions (12–
17) and numerous hydrodynamic or magneto-hydrodynamic simulations of various complexities and
dynamic ranges [e.g., (18–23)]. Many of the recent model development were stimulated by sub-mm
polarization/Faraday rotation measurements, providing stringent constraints on the accretion rate in the
innermost region (r <
∼ 102rs) of Sgr A*[e.g., (24)]. But controversies remain as to which model (if any)
may apply [e.g., (19,21)].
2
3. High-angular resolution observations of Sgr A* – such as those provided by the Chandra X-ray
Observatory — can in principle probe the accretion phenomenon not only in its innermost regions, but
also the outer boundary conditions at flow onset. However, there are substantial uncertainties regarding
the interpretation of the quiescent emission of Sgr A* which previous Chandra observations showed to
be extended with an intrinsic size of about 1.4 (3). How that emission is distributed within this region,
and how much is due to a bound accretion flow versus other components, remain unclear. Furthermore,
it has been proposed (3,25) that a substantial or even dominant fraction of the emission could arise from
a centrally-peaked population of coronally active, low-mass main-sequence stars around Sgr A*, which
is allowed by current near-infrared observations. This scenario predicts a 6.4 keV emission line with the
equivalent width (EW) in the range of 50 − 100 eV, due to fluorescence of photospheric weakly ionized
irons, irradiated by coronal flare X-rays. It is thus essential to test this hypothesis before we can assign
the X-ray emission to the accretion flow onto the SMBH.
We use data taken during the Sgr A* X-ray Visionary Program [XVP; (26)]. The ACIS-S (Advanced
CCD Imaging Spectrometer-Spectroscopy), combined with the HETG (High-energy Transmission Grat-
ing), was placed at the aim point of the telescope. The on-axis spatial resolution of Chandra is ∼ 0.4
(FWHM), whereas the spectral resolution of the 0th-order ACIS-S/HETG data is about a factor of ∼ 2
better than that of the previous ACIS-I observations and thus enables critical spectroscopic diagnostics
of the X-ray emission.
These observations reveal X-ray emission from Sgr A* that appears substantially more extended than
a point-like source [Fig. 1a; (26)]. After subtracting a point-like contribution, which accounts for 20%
of the total quiescent emission (26), an east-west-elongated X-ray enhancement emerges around Sgr A*
on ∼ 1 -1.5 scales (Fig. 1b). This relatively symmetric enhancement morphologically resembles the
so-called clockwise stellar disk, which is the most notable kinematically organized structure known for
the massive stars around Sgr A* (27,28). Irregular low-surface-brightness features (e.g., spurs toward the
north-east and south-east; Fig. 1b) appear on scales greater than the enhancement, but still roughly within
the Bondi radius. These features are softer (more prominent in the 1-4 keV band than in the 4-9 keV
3
4. band) than the smoothly-distributed background.
The quiescent X-ray emission is also spectrally distinct from the point-like flare emission (26), which
is considerably harder. The accumulated flare spectrum can be well characterized by a power law with
photon index 2.6(2.2, 3.0), and a foreground absorption column of NH = 16.6(14.1, 19.4) × 1022 cm−2
[see (29) for the definition of the uncertainties], consistent with the previous analysis of individual bright
flares (30,31). Because of the simplicity of the flare spectrum, this NH measurement can be considered
a reliable estimate of the foreground X-ray-absorbing column density along the sightline toward Sgr A*,
and hence a useful constraint in modeling the more complex spectrum of the quiescent X-ray emission.
In contrast, the quiescent spectrum shows prominent emission lines (Fig. 2). In addition to the
previously known Fe Kα emission at ∼ 6.7 keV, Kα lines of several other species (He- and H-like Ar,
He-like S and Ca), as well as He-like Fe Kβ are also apparent. We find that a single-temperature (1-T)
plasma with metal abundance set equal to zero describes the overall (continuum) shape of the observed
spectrum well, while individual Gaussians can be used to characterize the centroid, flux, and EW of six
most significant emission lines [Fig. 2a; (26)]. There is little sign of the diagnostic Kα emission lines
from neutral/weakly ionized Fe at ∼ 6.4 keV or H-like Fe at 6.97 keV.
We can reject the stellar coronal hypothesis, based on our temporal, spatial, and spectral results. First,
our spectrum does not confirm the presence of the 6.4-keV line, previously suggested by (25). Measuring
the 6.4-keV line, which is adjacent to the strong highly ionized Fe Kα line, is difficult when the spectral
resolution is poor, as was the case for the previous ACIS-I spectrum, because the measurement then
depends sensitively on the assumed thermal plasma model. Our measured upper limit to the EW of
the 6.4-keV line emission, 22 eV (26), is more than a factor of 2 below the range predicted before (25).
Second, the quiescent emission shows no significant variation on time scales of hours or days, as expected
from the sporadic giant coronal flares of individual stars. Third, if the bulk of the quiescent emission is
due to stellar coronal activity, then it should also account for some of the detected X-ray flares, especially
the relatively long and weak ones (25). However, no sign of any line emission, even the strong Fe Kα
line, is found in any flare spectra [individual or accumulated; (26,32)]. Fourth, the spatial distribution of
4
5. the weak flares is as point-like as the strong ones, in contrast to the extended quiescent emission (26).
Therefore, we conclude that neither flare nor quiescent emission originates from stellar coronal activity,
although the latter could still give a small (∼25%) contribution to the quiescent emission.
As described above, the diffuse X-ray emission on the scale of <
∼ 1.5 (or 1.5 × 105rs) morphologi-
cally resembles a gaseous disk with inclination angle and line-of-nodes similar to those of the stellar disk
around Sgr A*. This scale, a factor of >
∼ 2 smaller than rB, corresponds to the sound-crossing distance
over ∼ 102(Ta/107 K)−1/2 years, which is about the time since the last major burst of Sgr A*, as in-
ferred from X-ray light echoes [e.g., (33,34)]. The burst, making Sgr A* a factor of ∼ 106 brighter than
its present state over a period of several 102 years, could have substantially altered the surroundings, as
well as the accretion flow itself. A stable accretion flow would then need to be re-established gradually,
roughly at the sound-crossing speed. This flow would be expected to carry the net angular momentum of
the captured wind material with an orientation similar to that of the stars, which could explain the mor-
phological similarities. However, the recent hydrodynamic simulations of the stellar wind accretion (8)
suggest that a Keplerian motion-dominated flow should occur on much smaller scales (r <
∼ 0.1 ). If true,
then the plasma on larger scales must be supported mainly by large gradients of thermal, magnetic,
cosmic-ray, and/or turbulence pressures, as indicated in various simulations [e.g., (19)].
One can further use the relative strengths of individual lines as powerful diagnostics of the accretion
flow (35,36). X-ray emission lines trace the emission measure distribution as a function of plasma
temperature. The ionic fraction of He-like S (S XV), for example, peaks at kT ∼ 1.4 keV, while the
He-like Fe dominates in the temperature range of ∼ 1.5 − 7 keV and the H-like Fe peaks sharply at ∼ 9
keV. At temperatures >
∼ 12 keV, Fe becomes nearly fully ionized. Thus if the radial dependence of the
temperature can be modeled, the density or mass distribution as a function of radius can be inferred.
The extremely weak H-like Fe Kα line in the Sgr A* spectrum immediately suggests a RIAF with
a very low mass fraction of the plasma at kT >
∼ 9 keV, or a strong outflow at radii r >
∼ 104rs (26). Radi-
ally resolved analysis further shows that the X-ray spectrum becomes increasingly hard with decreasing
radius and that the line centroid and EW of the Fe Kα line also changes with the radius. These character-
5
6. istics can naturally be explained by the presence of plasma at a relatively low temperature in the region,
consistent with the onset of the RIAF from captured stellar wind material at r ∼ 105rs.
As detailed in (26), we can quantitatively check the consistency of the X-ray spectrum of the quies-
cent Sgr A* with various RIAF solutions. In particular, we can reject (with a null hypothesis probability
of 10−6) a no-outflow solution (i.e., a constant mass accretion rate along the accretion flow leading to
a radial plasma density profile n ∝ r−3/2+s, in which s = 0). This solution substantially over-predicts
the H-like Fe Kα line, while other lines are not fully accounted for. The predicted shape of the model
spectrum is also far too flat, resulting in a substantially reduced NH[= 8.0(7.6, 8.3)×1022 cm−2], incon-
sistent with other estimates. Therefore, the no-outflow solution can be firmly rejected, both statistically
and physically.
We find that a RIAF model with a flat radial density profile (i.e., s ∼ 1) provides an excellent fit to
both the continuum and lines data (Fig. 2b), and gives estimates of both the plasma metal abundance and
the foreground absorption column consistent with other independent measurements (26). With this fit, we
can infer the radial emission structure of the accretion flow. Although the line emission is dominated by
the outer, cooler region of the RIAF (r >
∼ 104rs), the innermost hot component contributes primarily to the
continuum emission, mostly via bremsstrahlung processes. We find that this latter contribution accounts
for only <
∼ 20% of the observed quiescent X-ray luminosity (consistent with the spatially decomposed
fraction), in stark contrast to the s = 0 solution, whose X-ray emission is completely dominated by the
innermost regions (r <
∼ 102rs). The inner accretion flow of Sgr A* is thus dimmer in the X-ray by almost
an order of magnitude than one would have assumed based on more luminous active galactic nuclei.
Further insight into the physical processes involved in the RIAF can be obtained from comparing
our X-ray measurements, most sensitive to the outer radial density profile, with existing constraints on
the accretion properties in the innermost region. For example, submillimeter Faraday rotation mea-
surements (24) set a lower limit to the accretion rate of 2 × 10−9M yr−1 into the innermost region.
Assuming that a large fraction of the Bondi accretion rate, ˙MB ∼ 1 × 10−5M yr−1, initially ends up
in the RIAF at a radius ∼ 105rs, then an s ∼ 1 density profile can hold down to radius ri ∼ 102rs. This
6
7. s ∼ 1 density profile over a broad radial range is consistent with various RIAF solutions [e.g., (14,17)]
and numerical simulations [e.g., (18)]. The Faraday rotation measurements also yield an upper limit to
the accretion rate of 2 × 10−7M yr−1, assuming that the magnetic field is near equipartition, ordered,
and largely radial in the RIAF (24). With this upper limit, assuming that ri ∼ 102rs we can infer s > 0.6
and hence θ >
∼ 0.6 for the radial temperature profile T ∝ r−θ of the RIAF. This constraint on θ places a
fundamental limit on thermal conduction-induced heat outflow (37).
The flat density profile of the flow (i.e., s ∼ 1) suggests the presence of an outflow that nearly
balances the inflow (26). As a result, <
∼ 1% of the matter initially captured by the SMBH reaches the
innermost region around Sgr A*, limiting the accretion power to <
∼ 1039 erg s−1. Much of this power is
probably used to drive the outflow, which could affect the environment of the nuclear region and even
beyond [e.g., (38)]. This combination of the low energy generation and high consumption rates of Sgr A*
naturally explains its low bolometric luminosity (a few times 1036 erg s−1) and its lack of powerful jets.
Observations of nearby elliptical galaxies with jet-inflated cavities in diffuse X-ray-emitting gas reveal
a relation between the jet and Bondi accretion powers (in units of 1043 erg s−1), Pjet ≈ 0.007P1.3
Bondi,
where PBondi is assumed to have a 10% efficiency of the Bondi mass accretion rate (39). We speculate
that the nonlinearity of this relation is due to increasing outflow rates with decreasing Bondi power,
leading to a reduced energy generation rate in the innermost region around a SMBH, where jets are
launched. Extrapolating the relation down to the case for Sgr A*, we may expect a jet to Bondi power
ratio of only ∼ 0.2%, consistent with the above inferred fractional mass loss due to the outflow.
The progress in understanding the accretion flow characteristics and orientation for our closest SMBH
will lead to key constraints for the modeling of such phenomena in general. For Sgr A* specifically these
results will impact models of the “shadow” of the SMBH [e.g., (40,41)], which can be measured by very
long baseline interferometry at (sub)millimeter wavelengths (42), the radiation from hydrodynamic in-
teractions of orbiting stars [e.g., S2; (43)] and the G2 object with ambient media at distances down to
∼ 103rs from the SMBH [e.g., (44)].
7
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Acknowledgments: We thank all the members of the Sgr A* Chandra XVP collaboration (http://www.sgra-
star.com/collaboration-members), which is supported by SAO grant GO2-13110A under NAS8-03060,
and are grateful to Chandra Mission Planning for their support during our 2012 campaign. QDW thanks
the hospitality of the Institute of Astronomy and the award of a Raymond and Beverley Sackler Distin-
guished Visitor fellowship. We also acknowledge the role of the Lorentz Center, Leiden; the Nether-
lands Organization for Scientific Research Vidi Fellowship (639.042.711; SM); funding support from
NASA through the Einstein Postdoctoral Fellowship (JN), grant PF2-130097, awarded by the Chandra
X-ray Center, which is operated by the SAO for NASA under contract NAS8-03060, and from NASA
through the SAO contract SV3-73016 to MIT for support of the Chandra X-ray Center, which is oper-
ated by the SAO for and on behalf of NASA under contract NAS8-03060, and NSFC and the 973 Project
(2009CB824800) of China. The X-ray data used here are available from asc.harvard.edu.
11
12. 20 60 100
IRS 13
G359.95−0.04
Sgr A*
(a) (b)
Figure 1: X-ray images of Sgr A* in quiescence. (a) An image constructed with the XVP 0th-order ACIS-
S/HETG data in the 1-9 keV band. The contours are at 1.3, 2.2, 3.7, 6.3, and 11 ×10−4 cts s−1 arcsec−2.
North is up and East is to the left. The dashed circle around Sgr A* marks its Bondi capture radius
(assumed to be 4 ). (b) A close-up of Sgr A*. The emission is decomposed into extended (color image)
and point-like (contour) components. The latter component is modeled with the net flare emission (26)
and is illustrated as the intensity contours at 2.4, and 5 counts per pixel. The straight dashed line marks
the orientation of the Galactic plane, whereas the dashed ellipse of a 1.5 semi-major axis illustrates the
elongation of the primary massive stellar disk, which has an inclination of i ∼ 127◦, a line-of-nodes
position angle of 100◦ (East from North), and a radial density distribution ∝ r−2 with a sharp inner cut
off at r ≈ 1 (27).
12
13. (a) (b)
Figure 2: The X-ray spectrum of Sgr A* in quiescence [extracted from the inner circle of 1.5 radius
and local-background-subtracted; (26)] and model fits: (a) zero-metallicity 1-T thermal bremsstrahlung
continuum plus various Gaussian lines (Table S.1); (b) the RIAF model with the best-fit γ = 2s/θ = 1.9,
where s and θ are the indexes parametrizing the density and temperature, respectively (26).
13
14. Supplementary Materials for
Dissecting X-ray-emitting Gas around the Center of our Galaxy
Q. D. Wang, M. A. Nowak, S. B. Markoff, F. K. Baganoff, S. Nayakshin, F. Yuan, J. Cuadra, J. Davis, J. Dexter,
A. C. Fabian, N. Grosso, D. Haggard, J. Houck, L. Ji, Z. Li, J. Neilsen, D. Porquet, F. Ripple, R. V. Shcherbakov
correspondence to: wqd@astro.umass.edu
This PDF file includes:
Materials and Methods
Figs. S1 to S3
Table S1
References (45-57)
Materials and Methods
The Chandra X-ray Visionary Project (XVP) to observe the Milky Way’s SMBH, Sgr A*, and the sur-
rounding inner few arcminutes, culminated in 38 observations for a total 3 mega-second exposure, taken
during February 6 to October 29, 2012. This Chandra Cycle 13 program utilized the High Energy Trans-
mission Gratings (HETG) in combination with the Advanced CCD Imaging Spectrometer-Spectroscopy
(ACIS-S) to accomplish high spatial, spectral, and temporal resolutions. Only the 0th-order ACIS-
S/HETG data from the observations are used in the present work. The spectral resolution of the data
is about a factor of ∼ 2 better than that of the previous Advanced CCD Imaging Spectrometer-imaging
(ACIS-I) observations (which suffered from a severe charge transfer inefficiency).
Data Reduction
The data are reduced via standard CIAO processing routines (version 4.5; Calibration Database ver-
sion 4.5.6). In particular, source detection is carried out for individual observations and later for the
merged data set. Sources detected within 3 of Sgr A* and with position errors less than 0.2 are used by
the routine reproject aspect to match each observation to the longest one (ObsID 13842), which is aligned
first to the radio position of Sgr A* [J2000: RA = 17h45m40.041s, Dec = −29◦00 28.12 ; (45)]. The
merged data can be treated approximately like a single observation, because the differences among the
14
15. pointing directions of individual observations are all within a 14 radius. Consistency checks for both
spectral and spatial results have also been carried out with existing ACIS-I observations. We find no
apparent calibration issues with the XVP ACIS-S/HETG data.
Decomposition of the Sgr A* data in the time domain
The data on Sgr A* are divided into two parts: one in various flare periods and the other in “flare-
free” or quiescent periods. A census of flares detected in the data can be found in (32). Different
detection algorithms give slightly different properties (e.g., peak fluxes), as well as different numbers of
flares, mostly at the low flux end. In this work, we have adopted the flare catalog from the detection
with the “Bayesian Blocks” routine [see Appendix of (32)]. The catalog contains 45 flares, a few more
than the number obtained with a Gaussian kernel detection scheme. Therefore, our adopted flare catalog
leads to a relatively conservative definition of the quiescent X-ray emission. Various tests, such as auto-
correlation, suggest that the quiescent emission is nearly a pure Poisson process of a constant photon flux;
the upper limit to the flare contribution to the emission within <
∼ 1.5 is 10%, consistent with the very flat
fluence function of the detected flares (32). The total exposure is 0.18 mega-seconds for the flares and
2.78 mega-seconds for the quiescent emission. The data accumulated from the quiescent periods (after
exposure correction) can be subtracted from those of the flare periods to obtain a net accumulated flare
spectrum or image.
Flare image and spatial decomposition of the Sgr A* quiescent X-ray emission
We construct an image of flares by stacking them and subtracting the exposure-corrected quiescent
contribution. The three brightest ones are excluded from this stacking to minimize potential pile-up
effects [two or more photons in a single “readout frame” being registered as a single event, or rejected as
a non X-ray event; (46)] The resultant net flare image (represented by the contours in Fig. 1b) is consistent
with the expected on-axis point-spread function of the instrument and shows a round morphology (with
statistical noise). The radial intensity profile of the Sgr A* flare emission is slightly narrower than that
of J174538.05-290022.3 (Fig. S.2). The profile of this latter source is included here as a reference of a
point-like distribution. The source shows high variability of X-ray intensity with time and is thus point-
15
16. like. With a spectrum indicative of strong absorption and projected only 27 west of Sgr A* (Fig. S.1),
the source is most likely located at the Galactic center or beyond. Therefore, the intensity profile of the
source can reasonably be used as an empirical reference of the combined angular dispersion of X-ray
radiation due to both the instrument point-spread function and the scattering by dust along the line of
sight.
To better assess the extended morphology of the quiescent emission, we subtract from it the flare
image scaled to minimize the roundness of the resultant image, but not to produce centrally depressed
or peanut-shaped morphology. The adopted scaling corresponds to a subtracted point-like component
accounting for 20% of the total quiescent emission — a fraction that is also consistent with the spectral
decomposition of the emission to be described later.
Spectral analysis
We adopt the same 1.5 radius region as used previously (25,47,48) to extract X-ray spectra of Sgr A*
in its flare and quiescent states. We also extract a “Sgr A*-halo” spectrum from a concentric annulus of
the inner and outer radii of 2 and 5 ; this outer bound is comparable to the Bondi radius within its
uncertainty. The Sgr A*-halo spectrum is not only used as the local background of the on-Sgr A*
spectrum, but analyzed to assess the ambient X-ray properties. To do so, we further obtain an “off-halo”
spectral background from a concentric 6 -18 annulus (Fig. S.1). The comet-shaped pulsar wind nebula
G359.95-0.04 (49), as well as the detected sources, are excluded from these annuli. Each on-source
spectrum is grouped to achieve a respective background-subtracted signal-to-noise ratio of >
∼ 3. The
accurate background subtraction is only moderately important for the quiescent Sgr A* spectrum. It has
a 1-9 keV count rate of 2.36×10−3 counts s−1, ∼ 25% of which can attributed to the local background,
as estimated in the Sgr A*-halo region. This fraction would be reduced by a factor of ∼ 2, if instead
the background estimated in the 6 -18 annulus is used. Such a difference in the background subtraction
would lead to some quantitative changes, but hardly affect the qualitative results presented in the present
paper.
All our spectral fits are conducted with the XSPEC package [(50); version 12.8.0]; model names
16
17. of the package are used unless otherwise noted. In particular, the spectrum of the optically-thin ther-
mal plasma at a certain temperature is modeled with APEC, which uses the ATOMDB code (v2.0.1),
assuming collisional ionization equilibrium (51). The metal abundances of the plasma, as well as the
foreground X-ray-absorbing gas, are relative to the interstellar medium (ISM) values given in (52). The
photoelectric absorption uses the Tuebingen-Boulder model [TBABS; (52)] with the cross-sections from
(53). An alternative version of the plasma model (VAPEC) is sometimes used to allow for abundance
variations of individual elements. Both the interstellar dust scattering (DUSTSC) and the CCD pile-up
(PILEUP) effects (31) are also accounted for.
We use a simple 1-T optically-thin thermal plasma to characterize the X-ray spectrum of Sgr A* in
quiescence. To properly account for distinct emission line features in the spectrum, we allow the abun-
dances of the relevant elements (S, Ar, Ca, and Fe, while all others are tied to C) to vary independently
in the fit. This VAPEC model with kT = 3.5(3.0, 4.0) keV gives an acceptable fit to the spectrum
(χ2/n.d.f. = 201/216). But, the fitted NH = 10.1(9.4, 11.1) × 1022 cm−2 is far too low to be consis-
tent with that inferred from the flare spectral analysis. Therefore, the model is unlikely to be physical.
Nevertheless, we find that the 1-T plasma with metal abundance set equal to zero gives a good (simple or
“model-independent”) characterization of the spectral continuum. We can then use individual Gaussians
to measure the emission lines (Fig. 2a). Table S.1 lists the fitted centroid, flux, EW, and identification for
each of the six most significant lines. The table also includes upper limits to the fluxes and EWs of the
diagnostic Kα emission lines from neutral/weakly ionized Fe and H-like Fe. Similar spectral analysis is
also conducted for the Sgr A*-halo region. The results are compared with those obtained for Sgr A* in
Fig. S.3) and in the main text.
Implement of the spectral model RIAF
While the quiescent X-ray spectrum obtained from the present work gives an unprecedented diag-
nostic capability to probe the accretion process of Sgr A*, it is still not possible to discriminate among
many possible spectral models or their combinations. Therefore, we primarily consider simple physi-
cal models, which capture key characteristics of the process. In particular, we test the RIAF solutions
17
18. [e.g., (12,14,15,17,54,55)], by implementing a general spectral model for them. In such a solution, the
inward radial motion as a function of the radius r is vr = vo(ro/r)1/2, or a fixed fraction of the Keplerian
orbital velocity (the subscript o is used to denote quantities at the outer radius ro); the accretion rate of
the RIAF is ˙M = ˙Mo(r/ro)s, where a positive s would indicate a net mass loss or outflow from the
flow. The mass conservation implies that the density profile is characterized by n = no(ro/r)3/2−s. The
temperature is T = To(ro/r)θ, increasing with decreasing radius due to the conversion of the gravita-
tional potential energy into heat (i.e., 0 < θ ≤ 1). These scaling relations have been largely confirmed
by various hydrodynamic and magneto-hydrodynamic simulations [e.g., (18,20)] as good approxima-
tions over broad radial ranges, although deviations may be expected at the accretion flow onset region
near the Bondi radius [e.g., (48,56); considerably larger than our chosen ro] and in the innermost region
(ri
<
∼ 102rs), where the electron temperature becomes decoupled from the ion temperature [e.g., (18,57)].
We calculate the X-ray spectrum of this outer RIAF model by integrating the corresponding differential
emission measure, dEM/dlog(T) ∝ (To/T)γ (where γ = 2s/θ), together with the emissivity function
of the APEC plasma over the temperature range from To to Ti. The radiation from radii smaller than ri
is simply modeled with an independent bremsstrahlung component (BREMSS) at Ti.
RIAF model fit to the quiescent X-ray spectrum
The RIAF model constructed above gives an excellent fit to the spectrum, both globally (χ2/n.d.f. =
187/218) and in terms of matching individual lines (Fig. 2b). The best-fit model gives γ = 1.9(1.4, 2.4).
If θ ∼ 1 as typically assumed [e.g., (14,17)], this suggests a very flat density profile of the flow (i.e.,
s ∼ 1), indicating an outflow mass-loss rate that nearly balances the inflow. The fitted metal abun-
dance, 1.5(1.1, 2.1), and absorption column, 13.8(12.2, 15.0)×1022 cm−2, are also consistent with their
expected values. The shape of the bremsstrahlung spectrum (hence the fit) in the Chandra band is in-
sensitive to the exact value of Ti. Its 95% lower limit is ∼ 108 K; but the best fit value appears to go
beyond the upper limit (∼ 109 K) of APEC. Thus, we fix Ti to this upper limit. The best-fit value and
the one-sided 95% upper limit of To are 0.96 × 107 K and 1.5 × 107 K. No lower limit is given; the
spectral contribution diminishes rapidly with decreasing temperature, because of the strong soft X-ray
18
19. Table S.1: Measurements of individual emission lines
Line energy flux EW ID, expected energy
(keV) (10−6 ph s−1 cm−2) (eV) (keV)
2.48 (2.44, 2.52) 2.5 (1.5, 3.8) 161 (101, 232) S XV, 2.461
3.10 (3.03, 3.16) 0.6 (0.3, 1.0) 64 (27, 104) Ar XVII, 3.140
3.35 (3.32, 3.39) 0.6 (0.3, 0.9) 72 (37, 109) Ar XVIII, 3.32
3.91 (3.86, 3.94) 0.4 (0.2, 0.6) 63 (31, 96) Ca XIX, 3.861
6.676 (6.660, 6.691) 1.2 (1.0, 1.4) 691 (584, 846) Fe XXV, 6.675
7.874 (7.737, 8.012) 0.2 (0.03, 0.4) 181 (91, 417) Fe XXV, 7.881
6.4 (fixed) 0 (0, 0.06) 0 (0, 22) Fe I-XVII, 6.4
6.973 (fixed) 0.07 (0, 0.11) 0 (0, 42) Fe XXVI, 6.973
Note: The dispersions of all the Gaussian lines, except for the strongest one (Fe XXV, 6.675 keV), are
fixed at 10−5 keV.
absorption along the sight line. We use the CFLUX convolution model to first estimate the unabsorbed
luminosity of Sgr A* in the 2-10 keV band as 3.4(2.9, 4.3) × 1033 erg s−1. We then estimate the lumi-
nosity of the BREMSS component to be 16(5, 23)% of the total flux of Sgr A*. This fraction is consistent
with the point source contribution component should have approximately included the relatively small
nonthermal contributions from undetected weak flares and photons inverse-Compton-scattered into the
X-ray band in the very inner region of the accretion flow [e.g., (55)]. Therefore, we conclude that the
fraction of the quiescent X-ray emission arises from the innermost region is about ∼ 20%.
19
20. 0.0 0.1 0.4 0.9 1.9 4.0 8.0 16.1 32.4 64.7 128.9
J174538.05
off−halo
Sgr A*
halo
Figure S.1: X-ray Overview of the field (56 × 46 ) around Sgr A*. The ACIS-S/HETG image is
constructed in the same way as Fig. 1a. The small central (dashed white) circle marks the on-Sgr A*
spectral extraction region, while the two large concentric (solid magenta and cyan) annuli outline the
Sgr A*-halo and off-halo background subtraction regions. The green box and small circles mark areas
that are significantly contaminated by an extended PWN and detected sources (1.5 times 70% energy-
encircled radii) and are thus excluded from the spectral extractions.
20
21. Figure S.2: Comparison of the radial 1-9 keV intensity profiles of Sgr A* in quiescence (diamonds) and
in flares (triangles), as well as J174538.05-290022.3 (crosses). Both the Sgr A* flare and J174538.05-
290022.3 profiles have been normalized to the intensity of the first bin of the quiescent Sgr A* profile.
This normalization is performed after subtracting the corresponding local background of each profile,
estimated as the median value in the 6 -8 range. The profiles are then shifted to the local background
level (the solid horizontal line) of the quiescent Sgr A* profile.
21
22. 10−5
10−4
10−3
Countss−1keV−1
6.5 7
−1
0
1
2
χ
Energy (keV)
Figure S.3: Comparison between the quiescent X-ray spectrum of Sgr A* (black; Fig. 2) and the Sgr A*-
halo spectrum (red; extracted from the 2 -5 annulus; Fig. S.1) in the Fe Kα complex region. Two
Gaussian lines are added into the fit to characterize the 6.4 keV and 6.973 keV lines, although the best-fit
model fluxes of the former line are zero for both spectra. the line centroid and EW of the Fe Kα line in
the spectrum of the Sgr A*-halo region, 6.63(6.60 - 6.65) keV and 0.29(0.22 - 0.37) keV, are substantially
different from those in the spectrum of Sgr A*(Table S.1).
22