ROSAT OBSERVATIONS OF THE LMC BE/X-RAY BINARY EXO-0531.1-6609 - THE LONG-TERM VARIABILITY

The Be/X-ray binary EXO 0531.1-6609 was in the field of view of 40 pointed ROSAT PSPC observations distributed over 4 years. Most of the observations yielded upper limits below 0.02 counts s(-1) consistent with several detections at this low-intensity level. A strong outburst lasting for more than two months was seen from March to May 1993. With a maximum observed intensity of 0.5 counts s(-1) the brightness of the outburst is comparable to that seen in 1983 by EXOSAT. The PSPC energy spectrum is consistent with a power law with photon index 1.5 as typically observed from this class of X-ray binaries.