scholarly journals Continuation of the X-ray monitoring of Sgr A*: the increase in bright flaring rate confirmed

2020 ◽  
Vol 636 ◽  
pp. A25
Author(s):  
E. Mossoux ◽  
B. Finociety ◽  
J.-M. Beckers ◽  
F. H. Vincent
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Milky Way ◽  
Detection Efficiency ◽  
Previous Method ◽  
Arrival Times ◽  
X Ray ◽  
Sagittarius A ◽  
Block Algorithm ◽  
Sgr A

Context. The supermassive black hole Sagittarius A* (Sgr A*) is located at the dynamical center of the Milky Way. In a recent study of the X-ray flaring activity from Sgr A* using Chandra, XMM-Newton, and Swift observations from 1999 to 2015, it has been argued that the bright flaring rate has increased from 2014 August 31 while the faint flaring rate decreased from around 2013 August. Aims. We tested the persistence of these changes in the flaring rates with new X-ray observations of Sgr A* performed from 2016 to 2018 (total exposure of 1.4 Ms). Methods. We reprocessed the Chandra, XMM-Newton, and Swift observations from 2016 to 2018. We detected 9 flares in the Chandra data and 5 flares in the Swift data that we added to the set of 107 previously detected flares. We computed the intrinsic distribution of flare fluxes and durations corrected for the sensitivity bias using a new method that allowed us to take the error on the flare fluxes and durations into account. From this intrinsic distribution, we determined the average flare detection efficiency for each Chandra, XMM-Newton, and Swift observation. After correcting each observational exposure for this efficiency, we applied the Bayesian blocks algorithm on the concatenated flare arrival times. As in the above-mentioned study, we also searched for a flux and fluence threshold that might lead to a change in flaring rate. We improved the previous method by computing the average flare detection efficiencies for each flux and fluence range. Results. The Bayesian block algorithm did not detect any significant change in flaring rate of the 121 flares. However, we detected an increase by a factor of about three in the flaring rate of the most luminous and most energetic flares that have occurred since 2014 August 30. Conclusions. The X-ray activity of Sgr A* has increased for more than four years. Additional studies about the overall near-infrared and radio behavior of Sgr A* are required to draw strong results on the multiwavelength activity of the black hole.

scholarly journals Sixteen years of X-ray monitoring of Sagittarius A*: Evidence for a decay of the faint flaring rate from 2013 August, 13 months before a rise in the bright flaring rate

2017 ◽  
Vol 604 ◽  
pp. A85 ◽  
Author(s):  
Enmanuelle Mossoux ◽  
Nicolas Grosso
Keyword(s):  
Detection Efficiency ◽  
Light Curves ◽  
Tidal Disruption ◽  
Spectral Parameters ◽  
Arrival Times ◽  
X Ray ◽  
Variable Position ◽  
Sagittarius A ◽  
The Mean ◽  
Sgr A

Context. X-ray flaring activity from the closest supermassive black hole Sagittarius A* (Sgr A*) located at the center of our Galaxy has been observed since 2000 October 26 thanks to the current generation of X-ray facilities. In a study of X-ray flaring activity from Sgr A* using Chandra and XMM-Newton public observations from 1999 to 2014 and Swift monitoring in 2014, it was argued that the “bright and very bright” flaring rate has increased from 2014 August 31. Aims. As a result of additional observations performed in 2015 with Chandra, XMM-Newton, and Swift (total exposure of 482 ks), we seek to test the significance and persistence of this increase of flaring rate and to determine the threshold of unabsorbed flare flux or fluence leading to any change of flaring rate. Methods. We reprocessed the Chandra, XMM-Newton, and Swift data from 1999 to 2015 November 2. From these data, we detected the X-ray flares via our two-step Bayesian blocks algorithm with a prior on the number of change points properly calibrated for each observation. We improved the Swift data analysis by correcting the effects of the target variable position on the detector and we detected the X-ray flares with a 3σ threshold on the binned light curves. The mean unabsorbed fluxes of the 107 detected flares were consistently computed from the extracted spectra and the corresponding calibration files, assuming the same spectral parameters. We constructed the observed distribution of flare fluxes and durations from the XMM-Newton and Chandra detections. We corrected this observed distribution from the detection biases to estimate the intrinsic distribution of flare fluxes and durations. From this intrinsic distribution, we determined the average flare detection efficiency for each XMM-Newton, Chandra, and Swift observation. We finally applied the Bayesian blocks algorithm on the arrival times of the flares corrected from the corresponding efficiency. Results. We confirm a constant overall flaring rate from 1999 to 2015 and a rise in the flaring rate by a factor of three for the most luminous and most energetic flares from 2014 August 31, i.e., about four months after the pericenter passage of the Dusty S-cluster Object (DSO)/G2 close to Sgr A*. In addition, we identify a decay of the flaring rate for the less luminous and less energetic flares from 2013 August and November, respectively, i.e., about 10 and 7 months before the pericenter passage of the DSO/G2 and 13 and 10 months before the rise in the bright flaring rate. Conclusions. The decay of the faint flaring rate is difficult to explain in terms of the tidal disruption of a dusty cloud since it occurred well before the pericenter passage of the DSO/G2, whose stellar nature is now well established. Moreover, a mass transfer from the DSO/G2 to Sgr A* is not required to produce the rise in the bright flaring rate since the energy saved by the decay of the number of faint flares during a long period of time may be later released by several bright flares during a shorter period of time.

scholarly journals Event horizon scale emission models for Sagittarius A*

2013 ◽  
Vol 9 (S303) ◽  
pp. 298-302
Author(s):  
J. Dexter
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Event Horizon ◽  
Near Infrared ◽  
Sagittarius A ◽  
Long Baseline ◽  
Black Hole Accretion ◽  
Emission Models ◽  
Infrared Interferometry ◽  
Sgr A

AbstractVery long baseline interferometry observations at millimeter wavelengths have detected source structure in Sgr A* on event horizon scales. Near-infrared interferometry will achieve similar resolution in the next few years. These experiments provide an unprecedented opportunity to explore strong gravity around black holes, but interpreting the data requires physical modeling. I discuss the calculation of images, spectra, and light curves from relativistic MHD simulations of black hole accretion. The models provide an excellent description of current observations, and predict that we may be on the verge of detecting a black hole shadow, which would constitute the first direct evidence for the existence of black holes.

scholarly journals Scale-invariance of black hole accretion: modelling emission from a black hole X-ray binary with relativistic accretion flow simulations

2019 ◽  
Vol 490 (4) ◽  
pp. 5353-5358
Author(s):  
M Mościbrodzka
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Thermal Emission ◽  
Broad Band ◽  
Scale Invariant ◽  
X Ray ◽  
Accretion Flow ◽  
Black Hole Accretion ◽  
Sgr A ◽  
Hole Accretion

ABSTRACT We model the non-thermal emission spectrum of the extremely sub-Eddington X-ray binary system A0620-00. It is believed that this non-thermal emission is produced by radiatively inefficient ‘quiescent’ accretion on to a stellar-mass black hole present in the system. We post-process general relativistic magnetohydrodynamics (GRMHD) simulations with multiwavelength, fully polarized, relativistic radiative transfer calculations to predict broad-band spectra and emission polarization levels for a range of electron models and accretion rates. We find that a model with strong coupling of electrons and ions in the accretion disc and accretion rate of only $\dot{M}=3\times 10^{-13} \, \rm [M_\odot \, yr^{-1}]$ is able to recover the observed X-ray spectral slope, as well as the excess of linear polarization detected in the source in the near-infrared (NIR)/optical bands. Our models constrain the spectral properties of a putative relativistic jet produced in this system. In addition, we show that the magnetized winds from our hot accretion flow carry away a small fraction of the orbital angular momentum of the binary, which is unable to explain the observed rapid orbital decay of the system. GRMHD simulations similar to the present ones are often used to explain emission from sub-Eddington supermassive black holes in Sgr A* or M87; the present simulations allow us to test whether some aspects of quiescent black hole accretion are scale-invariant.

scholarly journals Variable and polarized emission from SgrA*

2006 ◽  
Vol 2 (S238) ◽  
pp. 181-185
Author(s):  
A. Eckart ◽  
R. Schödel ◽  
L. Meyer ◽  
C. Straubmeier ◽  
M. Dovčiak ◽  
...  
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Galactic Center ◽  
Hot Spot ◽  
Massive Black Hole ◽  
X Ray ◽  
Sagittarius A ◽  
Polarized Emission

AbstractThe super-massive black hole in the Galactic Center (Sagittarius A*) is one of the most exciting targets in the sky. At a distance of ∼ 8 kpc it is about one hundred times closer than the second nearest nucleus of a similar galaxy, M31, and therefore the closest galactic nucleus that we can study. Here we report on the modeling of polarized near-infrared flare emission from SgrA* using a model in which a hot spot is moving on a relativistic orbit around the massive black hole. We also summarize the results from simultaneous radio/near-infrared/X-ray measurements of flare emission.

scholarly journals Statistical and theoretical studies of flares from Sagittarius A⋆

2016 ◽  
Vol 11 (S322) ◽  
pp. 31-38
Author(s):  
Ya-Ping Li ◽  
Qiang Yuan ◽  
Q. Daniel Wang ◽  
P. F. Chen ◽  
Joseph Neilsen ◽  
...  
Keyword(s):  
Black Hole ◽  
Solar Flares ◽  
Galactic Center ◽  
Theoretical Models ◽  
Spatial Dimension ◽  
X Ray ◽  
Sagittarius A ◽  
Multi Wavelength ◽  
Self Organized Criticality ◽  
Sgr A

AbstractMulti-wavelength flares have routinely been observed from the supermassive black hole, Sagittarius A⋆ (Sgr A⋆), at our Galactic center. The nature of these flares remains largely unclear, despite many theoretical models. We study the statistical properties of the Sgr A⋆ X-ray flares and find that they are consistent with the theoretical prediction of the self-organized criticality system with the spatial dimension S = 3. We suggest that the X-ray flares represent plasmoid ejections driven by magnetic reconnection (similar to solar flares) in the accretion flow onto the black hole. Motivated by the statistical results, we further develop a time-dependent magnetohydrodynamic (MHD) model for the multi-band flares from Sgr A⋆ by analogy with models of solar flares/coronal mass ejections (CMEs). We calculate the X-ray, infrared flare light curves, and the spectra, and find that our model can explain the main features of the flares.

scholarly journals Observations of NIR polarized light from Sagittarius A*

2013 ◽  
Vol 9 (S303) ◽  
pp. 283-287
Author(s):  
B. Shahzamanian ◽  
A. Eckart ◽  
M. Zamaninasab ◽  
G. Witzel ◽  
N. Sabha
Keyword(s):  
Black Hole ◽  
Adaptive Optics ◽  
Near Infrared ◽  
Polarized Light ◽  
Time Interval ◽  
Physical Conditions ◽  
Supermassive Black Hole ◽  
Sagittarius A ◽  
Linearly Polarized ◽  
Sgr A

AbstractWe present a brief overview of results obtained from near-infrared polarized observations of Sgr A*, which is associated with the supermassive black hole at the center of the Milky Way. The observations have been carried out using the NACO adaptive optics instrument at the VLT UT4 in the infrared Ks-band from 2004 to 2012. Several polarized flares have been observed in this time interval which allow us to determine the statistical properties of NIR linearly polarized light from Sgr A*. Linear polarization at 2.2 μm and its variations can help us to constrain the physical conditions of the accretion process around this supermassive black hole.

scholarly journals The (quite dark) stellar cluster around the supermassive black hole Sagittarius A* at the center of the Milky Way

2007 ◽  
Vol 3 (S245) ◽  
pp. 207-210
Author(s):  
Rainer Schödel ◽  
A. Eckart
Keyword(s):  
Black Hole ◽  
Adaptive Optics ◽  
Near Infrared ◽  
Milky Way ◽  
Infrared Imaging ◽  
Current Theory ◽  
Star Cluster ◽  
Massive Black Hole ◽  
Stellar Cluster ◽  
Sagittarius A

AbstractHigh-resolution seeing limited and adaptive optics near-infrared imaging observations of the stellar cluster within about one parsec of the massive black hole Sagittarius A* allow us to obtain a detailed picture of the structure of the nuclear star cluster of the Milky Way. We find that the stellar number counts and the diffuse light of the unresolved stellar population can be described very well by a stellar density function in the form of a broken-power law. This agrees well with theoretical predictions on the structure of a dynamically relaxed star cluster around a massive black hole. However, the cusp slope is found to be too shallow, which may be related to mixing of different stellar populations and continuous star formation, phenomena that are not taken into account by current theory. Mass densities larger than 107 solar masses per pc3 are reached within 0.1 pc of the central black hole. Intriguingly, up to several tens of percent of the total cluster mass in the central parsec may be in the form of dark stellar remnants.

scholarly journals Hot stars in the Galactic Center

1999 ◽  
Vol 193 ◽  
pp. 449-458
Author(s):  
Andreas Eckart ◽  
Thomas Ott ◽  
Reinhard Genzel ◽  
Dieter Lutz
Keyword(s):  
Black Hole ◽  
Near Infrared ◽  
Milky Way ◽  
Infrared Imaging ◽  
Galactic Center ◽  
Hot Stars ◽  
Massive Black Hole ◽  
Central Cluster ◽  
Short Period ◽  
Sgr A

The central parsec of our Galaxy is powered by a cluster of young massive hot stars which formed a few million years ago. Within that cluster the seven most luminous (L >105.75 L⊙) and moderately hot (T < 104.5 K) blue supergiants contribute half of the ionizing luminosity of that region. These stars probably formed when a dense cloud fell into the center < 107 years ago, was highly compressed there, and became gravitationally unstable. Over six years of high spatial resolution, near-infrared imaging and spectroscopy have made it possible to carry out a detailed investigation of the stars in the central cluster and its enclosed mass. As one result of a detailed variability study of the central cluster stars we found that the bright He I star IRS 16SW is a short-period variable with a period of ∼9.72 days. It is most likely an eclipsing binary with a lower mass limit of 100 solar masses. Line of sight velocities and proper motions have been measured for these hot stars (as well as ∼200 other stars) down to separations of less than five light days from the compact radio source Sgr A* at the dynamic center of the Milky Way. These confirmed measurements imply the presence of a central dark mass of 2.6 × 106 solar masses. The dark mass at the center of the Milky Way is currently the most compelling case for a massive black hole. Simple physical considerations show that this dark mass cannot consist of a stable cluster of stars, stellar remnants, substellar condensations or a degenerate gas of elementary particles but that at least 103 to 105 solar masses must be in the form of a massive black hole associated with Sgr A* itself.

scholarly journals NEAR-INFRARED AND X-RAY QUASI-PERIODIC OSCILLATIONS IN NUMERICAL MODELS OF Sgr A*

2012 ◽  
Vol 746 (1) ◽  
pp. L10 ◽  
Author(s):  
Joshua C. Dolence ◽  
Charles F. Gammie ◽  
Hotaka Shiokawa ◽  
Scott C. Noble
Keyword(s):  
Near Infrared ◽  
Numerical Models ◽  
Periodic Oscillations ◽  
X Ray ◽  
Sgr A

scholarly journals A Multi-Frequency Study of the Milky Way-Like Spiral Galaxy NGC 6744

2018 ◽  
Vol 35 ◽  
Author(s):  
Miranda Yew ◽  
Miroslav D. Filipović ◽  
Quentin Roper ◽  
Jordan D. Collier ◽  
Evan J. Crawford ◽  
...  
Keyword(s):  
Black Hole ◽  
Milky Way ◽  
Formation Rate ◽  
Radio Continuum ◽  
Starburst Galaxy ◽  
Radio Sources ◽  
Wide Field ◽  
Central Black Hole ◽  
X Ray ◽  
Continuum Data

AbstractWe present a multi-frequency study of the intermediate spiral SAB(r)bc type galaxy NGC 6744, using available data from the Chandra X-Ray telescope, radio continuum data from the Australia Telescope Compact Array and Murchison Widefield Array, and Wide-field Infrared Survey Explorer infrared observations. We identify 117 X-ray sources and 280 radio sources. Of these, we find nine sources in common between the X-ray and radio catalogues, one of which is a faint central black hole with a bolometric radio luminosity similar to the Milky Way’s central black hole. We classify 5 objects as supernova remnant (SNR) candidates, 2 objects as likely SNRs, 17 as H ii regions, 1 source as an AGN; the remaining 255 radio sources are categorised as background objects and one X-ray source is classified as a foreground star. We find the star-formation rate (SFR) of NGC 6744 to be in the range 2.8–4.7 M⊙~yr − 1 signifying the galaxy is still actively forming stars. The specific SFR of NGC 6744 is greater than that of late-type spirals such as the Milky Way, but considerably less that that of a typical starburst galaxy.

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