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\emissiontypeI K- alpha line at 6.40 keV, a giant molecular cloud M 0.66-0.02 known as the ``Sgr B2 cloud'' and an unusual X-ray source G 0.570-0.018. 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 Fe\emissiontypeXXV-K alpha line at 6.67 keV in the Galactic diffuse X-ray emission. This time variation is mostly due to M 0.66-0.02; the 6.40 keV line flux declined in 2001 and decreased to 60% in the time span 1994-2005. The other spot G 0.570-0.018 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.
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