A<i>CHANDRA</i>/HETGS CENSUS OF X-RAY VARIABILITY FROM Sgr A* DURING 2012

Abstract

We present the first systematic analysis of the X-ray variability of Sgr A*\nduring the Chandra X-ray Observatory's 2012 Sgr A* X-ray Visionary Project\n(XVP). With 38 High Energy Transmission Grating Spectrometer (HETGS)\nobservations spaced an average of 7 days apart, this unprecedented campaign\nenables detailed study of the X-ray emission from this supermassive black hole\nat high spatial, spectral and timing resolution. In 3 Ms of observations, we\ndetect 39 X-ray flares from Sgr A*, lasting from a few hundred seconds to\napproximately 8 ks, and ranging in 2-10 keV luminosity from ~1e34 erg/s to 2e35\nerg/s. Despite tentative evidence for a gap in the distribution of flare peak\ncount rates, there is no evidence for X-ray color differences between faint and\nbright flares. Our preliminary X-ray flare luminosity distribution dN/dL is\nconsistent with a power law with index -1.9 (+0.3 -0.4); this is similar to\nsome estimates of Sgr A*'s NIR flux distribution. The observed flares\ncontribute one-third of the total X-ray output of Sgr A* during the campaign,\nand as much as 10% of the quiescent X-ray emission could be comprised of weak,\nundetected flares, which may also contribute high-frequency variability. We\nargue that flares may be the only source of X-ray emission from the inner\naccretion flow.\n