The X-ray flaring properties of Sgr A* during six years of monitoring with Swift. (arXiv:1210.7237v1 [astro-ph.HE])

The X-ray flaring properties of Sgr A* during six years of monitoring with Swift. (arXiv:1210.7237v1 [astro-ph.HE]):
Starting in 2006, Swift has been targeting a region of \sim 21'X21' around
Sagittarius A* (Sgr A*) with the onboard X-ray telescope. The short,
quasi-daily observations offer an unique view of the long-term X-ray behavior
of the supermassive black hole. We report on the data obtained between 2006
February and 2011 October, which encompasses 715 observations with a total
accumulated exposure time of \sim 0.8 Ms. A total of six confirmed X-ray flares
were detected with Swift, which all had an average 2-10 keV luminosity of Lx
(1-4)E35 erg/s (assuming a distance of 8 kpc). This more than doubles the
number of such bright X-ray flares observed from Sgr A*. The most luminous
X-ray flare seen with Swift may have reached a 2-10 keV peak intensity of Lx
6E35 erg/s, which would make it the brightest X-ray flare detected so far. One
of the Swift-detected flares was considerably softer than the other five,
indicating that flares of similar intensity can have different spectral
properties. An additional ten candidate X-ray flares were detected with an
estimated average intensity of Lx (0.7-1)E35 erg/s (2-10 keV). The Swift
campaign allows us to constrain the occurrence rate of bright (Lx > 1E35 erg/s)
X-ray flares to be ~0.2-0.5 per day, which is consistent with previous
estimates. This analysis of the occurrence rate and properties of the X-ray
flares seen with Swift offers an important calibration point to asses whether
the flaring behavior of Sgr A* changes as a result of its interaction with the
gas cloud that is projected to make a close passage in 2013.