Sgr B2 hard X-ray emission with INTEGRAL after 2009: still detectable?. (arXiv:2110.07401v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kuznetsova_E/0/1/0/all/0/1">Ekaterina Kuznetsova</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Krivonos_R/0/1/0/all/0/1">Roman Krivonos</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Lutovinov_A/0/1/0/all/0/1">Alexander Lutovinov</a> (1,2), <a href="http://arxiv.org/find/astro-ph/1/au:+Clavel_M/0/1/0/all/0/1">Ma&#xef;ca Clavel</a> (3) ((1) Space Research Institute of the Russian Academy of Sciences, Moscow, Russia, (2) National Research University Higher School of Economics, Moscow, Russia, (3) Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France)

Molecular cloud Sgr B2 is a natural Compton mirror in the Central Molecular
Zone. An observed fading of the Sgr B2 X-ray emission in continuum and Fe
K$alpha$ 6.4 keV line indicates, as believed, a past X-ray flare activity of
the supermassive black hole Sgr A$^{star}$. The Sgr B2 was investigated by the
INTEGRAL observatory at hard X-rays in 2003-2009, showing a clear decay of its
hard X-ray emission. In this work, we present a long-term time evolution of the
Sgr B2 hard X-ray continuum after 2009, associated with the hard X-ray source
IGR J17475-2822 as observed by INTEGRAL. The 30-80 keV sky maps, obtained in
2009-2019, demonstrate a significant excess spatially consistent with IGR
J17475-2822. The observed 2003-2019 light curve of IGR J17475-2822 is
characterized by a linear decrease by a factor of $sim2$ until 2011, after
which it reaches a constant level of $sim1$ mCrab. The source spectrum above
17 keV is consistent with a power-law model with $Gamma=1.4$ and a high-energy
cut-off at $sim43$ keV. The Sgr B2 residual emission after $sim2011$ shows a
good correspondence with models of the X-ray emission due to the irradiation of
the molecular gas by hard X-rays and low-energy cosmic ray ions. We discuss the
possible origin of the residual Sgr B2 emission after 2011 within these models,
including theoretically predicted multiply-scattered emission.

Molecular cloud Sgr B2 is a natural Compton mirror in the Central Molecular
Zone. An observed fading of the Sgr B2 X-ray emission in continuum and Fe
K$alpha$ 6.4 keV line indicates, as believed, a past X-ray flare activity of
the supermassive black hole Sgr A$^{star}$. The Sgr B2 was investigated by the
INTEGRAL observatory at hard X-rays in 2003-2009, showing a clear decay of its
hard X-ray emission. In this work, we present a long-term time evolution of the
Sgr B2 hard X-ray continuum after 2009, associated with the hard X-ray source
IGR J17475-2822 as observed by INTEGRAL. The 30-80 keV sky maps, obtained in
2009-2019, demonstrate a significant excess spatially consistent with IGR
J17475-2822. The observed 2003-2019 light curve of IGR J17475-2822 is
characterized by a linear decrease by a factor of $sim2$ until 2011, after
which it reaches a constant level of $sim1$ mCrab. The source spectrum above
17 keV is consistent with a power-law model with $Gamma=1.4$ and a high-energy
cut-off at $sim43$ keV. The Sgr B2 residual emission after $sim2011$ shows a
good correspondence with models of the X-ray emission due to the irradiation of
the molecular gas by hard X-rays and low-energy cosmic ray ions. We discuss the
possible origin of the residual Sgr B2 emission after 2011 within these models,
including theoretically predicted multiply-scattered emission.

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