High-mass X-ray binaries

Abstract

High-mass X-ray binary (HMXB) systems were first identified in the early 1970s amongst the handful of mysterious bright X-ray sources found in the 1960s from brief sounding rocket and balloon flights. The launch of NASA’s Uhuru (SAS 1) satellite, which made the first all-sky X-ray survey, established the class. One of the first results from this mission was the discovery by Giacconi et al. (1971) of 4.8 s X-ray pulsation from Cen X-3 (Figure 1). Precise pulse timing and the observation of an eclipse of the pulsar showed that Cen X-3 is in a 2.1-day orbit around a massive early-type star (Schreier et al. 1972). Within the Uhuru error box of Cen X-3 Krzeminski (1974) identified the optical counterpart as a 13th magnitude highly reddened early OB-type star. It is ironic to note that if the radio astronomers had not discovered radio pulsars in 1967, then X-ray astronomy would surely have found them a few years later.Around the time of the launch of Uhuru, Bolton (1972) and Webster and Murdin (1972) identified the optical counter-part to the then anonymous X-ray source Cyg X-l (discovered by Bowyer et al 1965) with an OB supergiant HD226868. For a brief time it was thought that Cyg X-1 was also a pulsar (Oda et al. 1971), but it turned out the pulses were not coherent but rather a manifestation of “shot noise” (Terrell 1972), caused by chaotic energy release in the accretion disk around the black hole.