The Ultraviolet/Optical Continuum of Hercules X-1/HZ Herculis

Abstract

view Abstract Citations (27) References (30) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Ultraviolet/Optical Continuum of Hercules X-1/HZ Herculis Vrtilek, S. D. ; Cheng, F. H. Abstract We present observations of the binary X-ray pulsar system Hercules X-1/HZ Herculis taken with the International Ultraviolet Explorer (lUE) and several ground-based observatories as part of a multi- wavelength campaign conducted in 1993 August. The 1993 campaign found the source in an unusual state, with substantially reduced X-ray flux, and also revealed a significant reduction in ultraviolet flux observed around eclipse ingress and egress, which implies an absence of the normally observed excess attributed to X-ray heating of the disk. Comprehensive modeling of the ultraviolet and optical continuum flux suggests that the ultraviolet and optical light curves can be reproduced by assuming variations in Mdot alone; however, changes in accretion rate are insufficient to account for the observed drop in X-ray flux. Shifts in disk inclination angle and changes in mass accretion rate can consistently explain the observed changes in X-ray, ultraviolet, and optical fluxes. Changes in mass accretion rate and disk inclination angle may be related to shifts in the 35 day precession period, with the average mass accretion rate corresponding to the average 35 day period. The rapid fluctuations in soft X-ray flux, observed several times during the campaign, may be caused by rapid variation of the mass accretion rate. Publication: The Astrophysical Journal Pub Date: July 1996 DOI: 10.1086/177475 Bibcode: 1996ApJ...465..915V Keywords: STARS: INDIVIDUAL CONSTELLATION NAME: HERCULES X-1; STARS: INDIVIDUAL CONSTELLATION NAME: HZ HERCULIS; ULTRAVIOLET: STARS full text sources ADS | data products SIMBAD (3) MAST (1) INES (1)