# X-ray behaviour of Circinus X-1 - I: X-ray Dips as a diagnostic of periodic behaviour

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We examine the periodic nature of detailed structure particularly dips in the RXTE-ASM lightcurve of Circinus X-1. The significant phase wandering of the X-ray maxima suggests their identification with the response on a viscous timescale of the accretion disk to perturbation. We find that the X-ray dips provide a more accurate system clock than the maxima, and thus use these as indicators of the times of periastron passage. We fit a quadratic ephemeris to these dips, and find its predictive power for the X-ray lightcurve to be superior to ephemerides based on the radio flares and the full archival X-ray lightcurve. Under the hypothesis that the dips are tracers of the mass transfer rate from the donor, we use their occurrence rate as a function of orbital phase to explore the as yet unconstrained nature of the donor. The high $\dot{P}$ term in the ephemeris provides another piece of evidence that Cir X-1 is in a state of dynamical evolution, and thus is a very young post-supernova system. We further suggest that the radio synchrotron nebula immediately surrounding Cir X-1 is in fact the remnant of the event that created the compact object, and discuss briefly the evidence for and against such an interpretation.

Autor: W. I. Clarkson; P. A. Charles; N. Onyett

Fuente: https://archive.org/