A Closer Look at the Soft X-Ray Transient X1608-52: Long-Term Optical and X-Ray Observations
Abstract
We report long-term simultaneous optical and (RXTE) X-ray observations of the soft X-ray transient and low-mass X-ray binary X1608-52 spanning from 1999 to 2001. In addition to the usual X-ray outburst and quiescent states, X1608-52 also exhibits an extended low-intensity state, during which the optical counterpart, QX Nor, is found to be about 2 mag brighter than during quiescence. We detect optical photometric variability on a possible period of 0.5370 days with a semiamplitude of ~0.27 mag in the I band. The modulation could be orbital but is also consistent with a scenario invoking a superhump with decreasing period. We discuss the possibilities of distinguishing between the orbital- and superhump-period cases. Observations of QX Nor during quiescence indicate an F- to G-type main-sequence secondary, while theoretical considerations argue for an evolved mass donor. Only an evolved mass donor would satisfy the condition for the occurrence of superhumps.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 2002
- DOI:
- 10.1086/339034
- arXiv:
- arXiv:astro-ph/0112465
- Bibcode:
- 2002ApJ...568..901W
- Keywords:
-
- Accretion;
- Accretion Disks;
- Stars: Binaries: Close;
- Stars: Individual: Constellation Name: QX Normae;
- Stars: Neutron;
- Stars: Variables: Other;
- X-Rays: Binaries;
- Astrophysics
- E-Print:
- 26 pages, 10 figures, ApJ, in press