Long‐Term X‐Ray Variability of Circinus X‐1

We present an analysis of long term X-ray monitoring observations of CircinusX-1 (Cir X-1) made with four different instruments: Vela 5B, Ariel V ASM, GingaASM, and RXTE ASM, over the course of more than 30 years. We use Lomb-Scargleperiodograms to search for the ~16.5 day orbital period of Cir X-1 in each ofthese data sets and from this derive a new orbital ephemeris based solely onX-ray measurements, which we compare to the previous ephemerides obtained fromradio observations. We also use the Phase Dispersion Minimization (PDM)technique, as well as FFT analysis, to verify the periods obtained fromperiodograms. we obtain dynamic periodograms (both Lomb-Scargle and PDM) of CirX-1 during the RXTE era, showing the period evolution of Cir X-1, and alsodisplaying some unexplained discrete jumps in the location of the peak power.Comment: 19 pages, 8 figures, Late