Hard X-ray view of the past activity of Sgr A* in a natural compton mirror

Abstract

We report the association of the recently discovered hard X-ray source IGR J17475-2822 with the giant molecular cloud Sgr B2 in the Galactic Center region. The broad band (3-200 keV) spectrum of the source constructed from data of different observatories strongly supports the idea that the X-ray emission of Sgr B2 is Compton scattered and reprocessed radiation emitted in the past by the Sgr A* source. We conclude that 300-400 years ago Sgr A* was a low luminosity (L ≈ 1.5 × 1039 erg s-1 at 2-200 keV) AGN with a characteristic hard X-ray spectrum (photon index T a 1.8). We estimate the mass and iron abundance of the Sgr B2 scattering gas at 2 × 106 M⊙(r/10pc)2 and 1.9 solar, respectively (where r is the radius of the cloud).