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.

10 pages, 7 figures. Accepted to Astronomy & Astrophysics

References in corpus (12)

• HI4PI: A full-sky HI survey based on EBHIS and GASS
• The eROSITA X-ray telescope on SRG
• Systematic comparison of photoionised plasma codes with application to spectroscopic studies of AGN in X-rays
• INTEGRAL observations of Her X-1
• HZ Her: Stellar Radius from X-ray Eclipse Observations, Evolutionary State and a New Distance
• The Photoionized Accretion Disk in Her X-1
• Inversion of the decay of the cyclotron line energy in Her X-1
• An ionised accretion disc wind in Hercules X-1
• The cyclotron line energy in Her X-1: stable after the decay
• Swift/BAT and RXTE/ASM Observations of the 35-day X-ray Cycle of Hercules X-1
• A broad-band X-ray view of the precessing accretion disk and pre-eclipse dip in the pulsar Her X-1 with NuSTAR and XMM-Newton
• Modeling of 35-day superorbital cycle of $B$ and $V$ light curves of IMXB HZ Her/Her X-1

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