N. Degenaar, J. M. Miller, J. Kennea, N. Gehrels, R. Wijnands
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.
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http://arxiv.org/abs/1210.7237
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