ESA Science & Technology - Hard X-ray view of the past activity of Sgr A* in a natural Compton mirror

Publication date: 16 October 2004

Authors: Revnivtsev, M.G. et al.

Journal: Astronomy & Astrophysics
Volume: 425
Issue: 3
Page: L49-L52
Year: 2004

Copyright: ESO

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 Gamma ~ 1.8). We estimate the mass and iron abundance of the Sgr B2 scattering gas at 2×10⁶ M_Sun(r/10 pc)² and 1.9 solar, respectively (where r is the radius of the cloud).