Abstract
In this paper we review the discoveries made with EXOSAT during observations of Cir X-1. Type 1 X-ray bursts were seen in two observations. During the brightest burst, the energy flux was observed to saturate. If we assume this saturation is due to the Eddington limit then it is possible to estimate a distance to the source from the X-ray data alone. In another two observations Cir X-1 was in its high state. The peak energy flux during the high state exceeds the peak energy flux from the bursts by more than a factor of three. In one high-state observation 1.4 Hz quasi-periodic oscillations (QPO) were detected, and in the second high-state observation, QPO were seen to decline from 17 to 5 Hz as the X-ray flux slowly declined. Very high time resolution data taken during this period show the existence of a second, broad peak in the power spectrum near a frequency of 200 Hz.
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