X-ray Echo from the Sagittarius C Complex and 500-year Activity History of Sagittarius A*. (arXiv:1211.4529v1 [astro-ph.GA])

X-ray Echo from the Sagittarius C Complex and 500-year Activity History of Sagittarius A*. (arXiv:1211.4529v1 [astro-ph.GA]):
This paper presents the Suzaku results obtained for the Sagittarius (Sgr) C
region using the concept of X-ray reflection nebulae (XRNe) as the echo of past
flares from the super massive black hole, Sgr A*. The Sgr C complex is composed
of several molecular clouds proximately located in projected distance. The
X-ray spectra of Sgr C were analyzed on the basis of a view that XRNe are
located inside the Galactic center plasma X-ray emission with an oval
distribution around Sgr A*. We found that the XRNe are largely separated in the
line-of-sight position, and are associated with molecular clouds in different
velocity ranges detected by radio observations. We also applied the same
analysis to the Sgr B XRNe and completed a long-term light curve for Sgr A*
occurring in the past. As a new finding, we determined that Sgr A* was
experiencing periods of high luminosity already 500 years ago, which is longer
than the previously reported value. Our results are consistent with a scenario
that Sgr A* was continuously active with sporadic flux variabilities of Lx =
1-3 x 10^39 erg s^-1 in the past 50 to 500 years. The average past luminosity
was approximately 4-6 orders of magnitude higher than that presently observed.
In addition, two short-term flares of 5-10 years are found. Thus, the past
X-ray flare should not be a single short-term flare, but can be interpreted as
multiple flares superposed on a long-term high state.