Extreme Ultraviolet Explorer Observations of Hercules X-1 over a 35 Day Cycle
Abstract
Observations of Hercules X-1 by the Extreme Ultraviolet Explorer covering most of the 35 day cycle are reported here. This is the only long extreme ultraviolet (EUV) observation of Her X-1. Simultaneous X-ray observations with the Rossi X-ray Timing Explorer All-Sky Monitor (RXTE/ASM) X-ray show that Her X-1 is in an X-ray anomalous low state. The first 4 days are also observed with the RXTE proportional counter array (PCA), which shows that the X-ray properties are nearly the same as for normal low states in Her X-1 with flux reduced by a factor of 2. In contrast, the EUV emission from Her X-1 is reduced by a factor of ~4 compared to normal low states. The twisted-tilted accretion disk responsible for the normal 35 day X-ray cycle can be modified to explain this behavior. An increased disk twist reduces the X-ray illumination of HZ Her by a factor of ~2 and of the disk surface by a somewhat larger factor, leading to a larger reduction in EUV flux compared to X-ray flux.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 2010
- DOI:
- 10.1088/0004-637X/715/2/897
- Bibcode:
- 2010ApJ...715..897L
- Keywords:
-
- binaries: eclipsing;
- stars: individual: HZ Her/Her X-1;
- stars: neutron