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Issue A&A
Volume 425, Number 3, October III 2004
Page(s) L49 - L52
Section Letters
DOI 10.1051/0004-6361:200400064



A&A 425, L49-L52 (2004)
DOI: 10.1051/0004-6361:200400064

Letter

Hard X-ray view of the past activity of Sgr A $^{\star}$ in a natural Compton mirror

M. G. Revnivtsev1, 2, E. M. Churazov1, 2, S. Yu. Sazonov1, 2, R. A. Sunyaev1, 2, A. A. Lutovinov1, M. R. Gilfanov1, 2, A. A. Vikhlinin1, 3, P. E. Shtykovsky1 and M. N. Pavlinsky1

1  Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia
    e-mail: revnivtsev@hea.iki.rssi.ru
2  Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85740 Garching bei München, Germany
3  Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA

(Received 11 August 2004 / Accepted 31 August 2004 )

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 $^{\star}$ source. We conclude that 300-400 years ago Sgr A $^{\star}$ was a low luminosity ( $L\approx 1.5\times 10^$ erg s -1 at 2-200 keV) AGN with a characteristic hard X-ray spectrum (photon index $\Gamma\approx 1.8$ ). We estimate the mass and iron abundance of the Sgr B2 scattering gas at $2\times 10^{6}~M_\odot(r/10\,{\rm pc})^2$ and 1.9 solar, respectively (where r is the radius of the cloud).


Key words: Galaxy: center -- ISM: clouds: individual: Sgr B2 -- X-rays: ISM

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