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arXiv · 2102.12983

Observations of Her X-1 in low states during SRG/eROSITA all-sky survey

N. I. Shakura·D. A. Kolesnikov·P. S. Medvedev·R. A. Sunyaev·M. R. Gilfanov·K. A. Postnov·S. V. Molkov
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Abstract

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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N. I. Shakura, D. A. Kolesnikov, P. S. Medvedev, R. A. Sunyaev, M. R. Gilfanov, K. A. Postnov, S. V. Molkov. 2021-02-25. Observations of Her X-1 in low states during SRG/eROSITA all-sky survey. https://doi.org/10.1051/0004-6361/202040145

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