Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Hard X-ray view of the past activity of Sgr A* in a natural Compton
  mirror   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 ~ 1.5e39 erg/s 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 2e6 Msun (r/10pc)^2 and 1.9 solar, respectively
(where r is the radius of the cloud).

11
The categories of this paper are: hep-lat
21
The categories of this paper are: adap-org
28
The categories of this paper are: alg-geom
19
The categories of this paper are: eess
27
The categories of this paper are: comp-gas
16
The categories of this paper are: stat
34
The categories of this paper are: chem-ph
15
The categories of this paper are: nucl-ex
36
The categories of this paper are: cmp-lg
2
The categories of this paper are: math
8
The categories of this paper are: hep-ex
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat