The Spectral and Temporal Variability of the X-Ray Transient 4U1630-47

We present the results of four observations made by the European Space Agency's EXOSAT Observatory of the X-ray transient 4U1630-47 during its 1984 outburst. We observed marked spectral changes as the source decayed from a maximum observed intensity of 8×10^-9 erg/cm²/sec (1.5 10 keV). The spectrum could be modelled by a soft ‘thermal-like’ component with a high energy power-law tail. The relative contribution of the soft to hard component decreased as the total luminosity decreased. We compare these changes with those observed from the black hole candidate Cyg X-1 when it transitions from a high to a low state. In addition we report the discovery of short timescale intensity variations (down to ∼ 50 msec) with a characteristic timescale of ∼ 20 sec. We present a precise position for this unidentified source.