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Time Variability of the Neutral Iron Lines from the Sgr B2 Region and its Implication of a.pdf

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Time Variability of the Neutral Iron Lines from the Sgr B2 Region and its Implication of a

a r X i v : 0 8 0 3 .1 5 2 8 v 1 [ a s t r o - p h ] 1 1 M a r 2 0 0 8 PASJ: Publ. Astron. Soc. Japan , 1–??, c? 2008. Astronomical Society of Japan. Time Variability of the Neutral Iron Lines from the Sgr B2 Region and its Implication of a Past Outburst of Sgr A? Tatsuya Inui, Katsuji Koyama, Hironori Matsumoto and Takeshi Go Tsuru Department of Physics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502 inuit@cr.scphys.kyoto-u.ac.jp (Received 2008 January 15; accepted 2008 February 29) Abstract We investigate long-term X-ray behaviors from the Sgr B2 complex using archival data of the X-ray satellites Suzaku, XMM-Newton, Chandra and ASCA. The observed region of the Sgr B2 complex includes two prominent spots in the Fe I K-α line at 6.40 keV, a giant molecular cloud M0.66?0.02 known as the “Sgr B2 cloud” and an unusual X-ray source G0.570?0.018. Although these 6.40 keV spots have spatial extensions of a few pc scale, the morphology and flux of the 6.40 keV line has been time variable for 10 years, in contrast to the constant flux of the FeXXV-Kα line at 6.67 keV in the Galactic diffuse X-ray emission. This time variation is mostly due to M0.66?0.02; the 6.40 keV line flux declined in 2001 and decreased to 60% in the time span 1994–2005. The other spot G0.570?0.018 is found to be conspicuous only in the Chandra observation in 2000. From the long-term time variability (～10 years) of the Sgr B2 complex, we infer that the Galactic Center black hole Sgr A? was X-ray bright in the past 300 year and exhibited a time variability with a period of a few years. Key words: Galaxy:center — ISM:clouds — ISM:individual (Sagittarius B) — X-rays:individual (Sagittarius B) — X-rays:ISM 1. Introduction Our Galactic Center (GC) black hole, Sgr A?, has a mass of 4× 106M⊙ (Eisenhauer et al. 2005; Ghez et al. 2005), but is quiescent with an X-ray luminosity of only 1033–34 ergs s?1 (Baganoff et al. 2001), which is many orders of magnitude smaller than that of