Modeling of 35-day superorbital cycle of $B$ and $V$ light curves of IMXB HZ Her/Her X-1

Abstract

The X-ray binary Her X-1 consists of an accreting neutron star and the optical component HZ Her. The 35-day X-ray superorbital variability of this system is known since its discovery in 1972 by the Uhuru satellite and is believed to be caused by forced precession of a warped accretion disk tilted to the orbital plane. We argue that the observed features of the 35-day optical variability of HZ Her can be explained by free precession of the neutron star with a period close to that of the forced disk. The model parameters include a) the X-ray luminosity of the neutron star; b) the optical flux from the accretion disk; c) the tilt of the inner and outer edges of the accretion disk. A possible synchronization mechanism based on the coupling between the neutron star free precession and the dynamical action of non-stationary gas streams is discussed.

12 pages, 11 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal

References in corpus (2)

• HZ Her: Stellar Radius from X-ray Eclipse Observations, Evolutionary State and a New Distance
• Two ~35 day clocks in Her X-1: evidence for neutron star free precession

Cited by in corpus (4)

• Evidence for neutron star triaxial free precession in Her X-1 from Fermi/GBM pulse period measurements
• Observations of Her X-1 in low states during SRG/eROSITA all-sky survey
• 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