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Hard X-ray light curves of high-mass X-ray binaries

Abstract:

Using the 9 years of continuous data now available from the Burst and Transient Source Experiment (BATSE) aboard CGRO, we have measured orbital periods and produced folded light curves for eight high-mass X-ray binaries (HMXB). Given the length of the data sets, our determinations are based on many more binary orbits than previous investigations. Thus our source detections have a high statistical significance and we are able to follow long-term trends in X-ray output. In particular, we focus on two systems: A0538-668 and EXO2030+375, both HMXBs exhibiting Type I outbursts. Recent work on A0538-668 reported a 16.65-d optical variability caused by the orbital period, but only seen during minima of a longer-term variability at 421 d. We searched for this signal in the BATSE data set but we found no evidence for such a modulation and place an upper limit of 3.0 × 10−3 photon cm−2 s−1 in the …