Observations of Her X-1 in low states during SRG/eROSITA all-sky survey. (arXiv:2102.12983v1 [astro-ph.HE])

Observations of Her X-1 in low states during SRG/eROSITA all-sky survey. (arXiv:2102.12983v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Shakura_N/0/1/0/all/0/1">N. I. Shakura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kolesnikov_D/0/1/0/all/0/1">D. A. Kolesnikov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Medvedev_P/0/1/0/all/0/1">P. S. Medvedev</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sunyaev_R/0/1/0/all/0/1">R. A. Sunyaev</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gilfanov_M/0/1/0/all/0/1">M. R. Gilfanov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Postnov_K/0/1/0/all/0/1">K. A. Postnov</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Molkov_S/0/1/0/all/0/1">S. V. Molkov</a>

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) instrument
onboard the Russian-German `Spectrum-Roentgen-Gamma’ (SRG) mission observed the
Her X-1/HZ Her binary system in multiple scans over the source during the first
and second SRG all-sky surveys. Both observations occurred during a low state
of the X-ray source when the outer parts of the accretion disk blocked the
neutron star from view. The orbital modulation of the X-ray flux was detected
during the low states. We argue that the detected X-ray radiation results from
scattering of the emission of the central source by three distinct regions: (a)
an optically thin hot corona with temperature $sim (2-4) times 10^6$ K above
the irradiated hemisphere of the optical star; (b) an optically thin hot halo
above the accretion disk; and (c) the optically thick cold atmosphere of the
optical star. The latter region effectively scatters photons with energies
above $5-6$ keV.

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) instrument
onboard the Russian-German `Spectrum-Roentgen-Gamma’ (SRG) mission observed the
Her X-1/HZ Her binary system in multiple scans over the source during the first
and second SRG all-sky surveys. Both observations occurred during a low state
of the X-ray source when the outer parts of the accretion disk blocked the
neutron star from view. The orbital modulation of the X-ray flux was detected
during the low states. We argue that the detected X-ray radiation results from
scattering of the emission of the central source by three distinct regions: (a)
an optically thin hot corona with temperature $sim (2-4) times 10^6$ K above
the irradiated hemisphere of the optical star; (b) an optically thin hot halo
above the accretion disk; and (c) the optically thick cold atmosphere of the
optical star. The latter region effectively scatters photons with energies
above $5-6$ keV.

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