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Journal Article

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

MPS-Authors
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Medvedev,  P. S.
MPI for Astrophysics, Max Planck Society;

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Sunyaev,  R. A.
High Energy Astrophysics, MPI for Astrophysics, Max Planck Society;

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Gilfanov,  M. R.
High Energy Astrophysics, MPI for Astrophysics, Max Planck Society;

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Citation

Shakura, N. I., Kolesnikov, D. A., Medvedev, P. S., Sunyaev, R. A., Gilfanov, M. R., Postnov, K. A., et al. (2021). Observations of Her X-1 in low states during SRG/eROSITA all-sky survey. Astronomy and Astrophysics, 648: A39. doi:10.1051/0004-6361/202040145.


Cite as: https://hdl.handle.net/21.11116/0000-0008-EDD3-F
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 ~(2−4) × 106 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.