Observations of a partial X-ray eclipse in the long-period low mass X-ray binary 2S 0921-630.
Abstract
A partial eclipse of the X-ray flux from 2S 0921-630 has been recorded for the first time, using the EXOSAT satellite. The time of the X-ray eclipse agrees with an extrapolation of the ephemeris of optical dips in 2S 0921-630, strongly supporting the hypothesis that 2S 0921-630 is an eclipsing binary with a period of just over 9 day. The X-ray eclipse lasts for over 1 day and has a smooth ingress and egress. At mid-eclipse the source flux drops to ≡30 per cent of its pre-eclipse value. The results of another, shorter, X-ray observation, also made at the predicted time of eclipse centre, suggest that the X-ray eclipse is a stable feature. The partial nature of the X-ray eclipse leads to the hypothesis that the binary companion in 2S 0921-630 obscures an extended medium which is scattering X-rays from a central, compact source into the line-of-sight. A simple model for the X-ray eclipse combined with optical radial velocity data suggests that the companion star in 2S 0921-630 is undermassive for its size compared to a normal, isolated star.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- May 1987
- DOI:
- 10.1093/mnras/226.2.423
- Bibcode:
- 1987MNRAS.226..423M
- Keywords:
-
- Accretion Disks;
- Eclipsing Binary Stars;
- Stellar Spectra;
- X Ray Binaries;
- Eclipses;
- Satellite Observation;
- Stellar Mass;
- Stellar Radiation;
- Astrophysics