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تسجيل مستخدم جديدNo sign of G2s encounter affecting Sgr A*s X-ray flaring rate from $Chandra$ observations
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An unusual object, G2, had its pericenter passage around Sgr A*, the $4times10^6$ M$_odot$ supermassive black hole in the Galactic Centre, in Summer 2014. Several research teams have reported evidence that following G2s pericenter encounter the rate of Sgr A*s bright X-ray flares increased significantly. Our analysis carefully treats varying flux contamination from a nearby magnetic neutron star and is free from complications induced by using data from multiple X-ray observatories with different spatial resolutions. We test the scenario of an increased bright X-ray flaring rate using a massive dataset from the textit{Chandra X-ray Observatory}, the only X-ray instrument that can spatially distinguish between Sgr A* and the nearby Galactic Centre magnetar throughout the full extended period encompassing G2s encounter with Sgr A*. We use X-ray data from the 3 Ms observations of the textit{Chandra} textit{X-ray Visionary Program} (XVP) in 2012 as well as an additional 1.5 Ms of observations up to 2018. We use detected flares to make distributions of flare properties. Using simulations of X-ray flares accounting for important factors such as the different $Chandra$ instrument modes, we test the null hypothesis on Sgr A*s bright (or any flare category) X-ray flaring rate around different potential change points. In contrast to previous studies, our results are consistent with the null hypothesis; the same model parameters produce distributions consistent with the observed ones around any plausible change point.
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This paper reports measurements of Sgr A* made with NACO in L -band (3.80 um), Ks-band (2.12 um) and H-band (1.66 um) and with VISIR in N-band (11.88 um) at the ESO VLT, as well as with XMM-Newton at X-ray (2-10 keV) wavelengths. On 4 April, 2007, a
very bright flare was observed from Sgr A* simultaneously at L-band and X-ray wavelengths. No emission was detected using VISIR. The resulting SED has a blue slope (beta > 0 for nuL_nu ~ nu^beta, consistent with nuL_nu ~ nu^0.4) between 12 micron and 3.8 micron. For the first time our high quality data allow a detailed comparison of infrared and X-ray light curves with a resolution of a few minutes. The IR and X-ray flares are simultaneous to within 3 minutes. However the IR flare lasts significantly longer than the X-ray flare (both before and after the X-ray peak) and prominent substructures in the 3.8 micron light curve are clearly not seen in the X-ray data. From the shortest timescale variations in the L-band lightcurve we find that the flaring region must be no more than 1.2 R_S in size. The high X-ray to infrared flux ratio, blue nuL_nu slope MIR to L -band, and the soft nuL_nu spectral index of the X-ray flare together place strong constraints on possible flare emission mechanisms. We find that it is quantitatively difficult to explain this bright X-ray flare with inverse Compton processes. A synchrotron emission scenario from an electron distribution with a cooling break is a more viable scenario.
Over the last decade, X-ray observations of Sgr A* have revealed a black hole in a deep sleep, punctuated roughly once per day by brief flares. The extreme X-ray faintness of this supermassive black hole has been a long-standing puzzle in black hole
accretion. To study the accretion processes in the Galactic Center, Chandra (in concert with numerous ground- and space-based observatories) undertook a 3 Ms campaign on Sgr A* in 2012. With its excellent observing cadence, sensitivity, and spectral resolution, this Chandra X-ray Visionary Project (XVP) provides an unprecedented opportunity to study the behavior of the closest supermassive black hole. We present a progress report from our ongoing study of X-ray flares, including the brightest flare ever seen from Sgr A*. Focusing on the statistics of the flares and the quiescent emission, we discuss the physical implications of X-ray variability in the Galactic Center.
We analyze the two brightest Chandra X-ray flares detected from Sagittarius A*, with peak luminosities more than 600 x and 245 x greater than the quiescent X-ray emission. The brightest flare has a distinctive double-peaked morphology --- it lasts 5.
7 ksec ($sim 2$ hours), with a rapid rise time of 1500 sec and a decay time of 2500 sec. The second flare lasts 3.4 ksec, with rise and decay times of 1700 sec and 1400 sec. These luminous flares are significantly harder than quiescence: the first has a power law spectral index $Gamma = 2.06pm 0.14$ and the second has $Gamma = 2.03pm 0.27$, compared to $Gamma = 3.0pm0.2$ for the quiescent accretion flow. These spectral indices (as well as the flare hardness ratios) are consistent with previously-detected Sgr A* flares, suggesting that bright and faint flares arise from similar physical processes. Leveraging the brightest flares long duration and high signal-to-noise, we search for intraflare variability and detect excess X-ray power at a frequency of $ u approx 3$ mHz, but show that it is an instrumental artifact and not of astrophysical origin. We find no other evidence (at the 95% confidence level) for periodic or quasi-periodic variability in either flares time series. We also search for non-periodic excess power but do not find compelling evidence in the power spectrum. Bright flares like these remain our most promising avenue for identifying Sgr A*s short timescale variability in the X-ray, which may probe the characteristic size scale for the X-ray emission region.
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und it. We report the result of the fully three-dimensional simulation of the evolution of G2 during the first pericenter passage. The strong tidal force by the SMBH stretches the cloud along its orbit, and compresses it strongly in the vertical direction, resulting in the heating up and flaring up of the cloud. The bolometric luminosity will reach the maximum of $sim100 L_{odot}$. This flare should be easily observed in the near infrared.
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