Circinus X-1

Circinus X-1

A luminous galactic X-ray source, showing recurrent flaring at a 16.6 day period. Spectral characteristics and variability on timescales down to milliseconds, similar to Cygnus X-1, initially suggested Cir X-1 as a black hole candidate. Discovery by EXOSAT of X-ray bursts have now shown that Cir X-1 is more likely to be a neutron star in an eccentric 16.6 day orbit with an early-type nondegenerate companion star. More recent observations with Asca suggest the rapid X-ray variability may result from dense gas clouds passing across in front of the X-ray emission region.
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