A0538-66: The Most Powerful X-ray Star

Observations of the X-ray transient A 0538-66 are discussed in order to characterize the physical nature of the object. Discovered with the Ariel 5 X ray satellite in 1977, A 0538-66 displayed an outburst period of about 16.6 days, and was correlated with optical observations of visible flares detected for 50 yr. The object's redshift confirmed its location in the LMC, but its X-ray brightness exceeds the Eddington limit. Data from the IUE has supported a model consisting of a neutron star in an eccentric orbit and siphoning mass from a companion giant B star. One revolution of the compact star around the giant draws a plume of material into a cloud around the giant, and the next orbit features a collision with the cloud at 500 km/sec, producing the dramatic X-ray outburst. The bursts ended in 1982.