Persistent Emission and Bursts from Aquila X-1 Observed by Einstein

The recurrent transient/X-ray burster Aql X-1 was observed by the Einstein satellite during its outburst in 1979 March and April. Thermal bremsstrahlung provided good spectral fits for eight out of a total of 10 observations; however, the X-ray spectrum of Aql X-1 is also well fitted by a two-component model in which radiation comes from a boundary layer and from an irradiated accretion disk. Two bursts were recorded by the Einstein MPC instrument. The light curves of these bursts are presented. The source was also observed half a year after the outburst. Its quiescent flux was then some 440 times lower than the maximum persistent flux value observed during the outburst.