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

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.

arXiv comment10 pages, 7 figures. Accepted to Astronomy & Astrophysics

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Cited by in corpus (3)

• Determination of X-ray pulsar geometry with IXPE polarimetry
• The Evolution of the Orbital Light-curve of Hercules X-1 with 35-day Phase
• On the nature of the 35-day cycle in HZ Her/Her X-1