Astronomy and Astrophysics X-ray off States and Optical Variability in Cal 83


CAL 83 was one of the first supersoft X-ray binaries (SSBs) to be discovered and is considered to be the prototype of its class. In 15 X-ray observations between 1983–1997 it was observed to have nearly constant X-ray luminosity and temperature, with the exception of one off-state in 1996 (Kahabka et al. 1996). We report on a second X-ray off-state, discovered with a Chandra ACIS-S observation in November 1999. We consider the long-term X-ray and MACHO optical light curves. We find that, during more than 7 years of monitoring by the MACHO team, CAL 83 has exhibited distinct and well-defined low, intermediate, and high optical states. Transitions between states are not accompanied by color variations. We also find that both X-ray off states were observed during optical high states and were followed by optical low states within ∼ 50 days. We discuss possible explanations for the observed optical and X-ray variations. While photospheric adjustments might account for the variations in soft X-ray flux, optical variations can be explained only by invoking changes in the accretion disk, which is the primary source of optical radiation.

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@inproceedings{Stefano2002AstronomyAA, title={Astronomy and Astrophysics X-ray off States and Optical Variability in Cal 83}, author={Rosanne Di Stefano}, year={2002} }