Galactic X-ray sources and their radio counterparts.

A 5200 cm2 , xenon-filled, multiwire proportional counter of 21 cm depth has been constructed for balloon-borne X-ray astronomy. The telescope is sensitive to photons in the energy range 10 - 100 keV and is surrounded on all sides, except the entrance window, by a Sn/Cu graded shield and anti-coincidence guard counters. The counter and 7¬¨‚àû x 20 ¬¨‚àûFWHM collimator were contained within an hermetically sealed aluminium pressure vessel of 1 metre diameter having expandable mylar ends. Counter pulses were pulse-height-analysed into 20 channels and telemetered, together with count rate data (0.5 ms sample rate) and house keeping data. The telescope was equatorially mounted on a magnetically referenced, reaction wheel servo-stabilized platform. Pointing under ground control to within 0 05 of a specified source position was achieved during flights in December 1976 and November 1978. On line, quick-look, analysis of the telemetered data with a PDP 11/10 computer enabled the observers to immediately assess the telescope performance and attempt to rectify any problems by radio command. A complete description of the telescope system and the payload performance during balloon flights in December 1976 and November 1978 is presented. Problems encountered with outgassing of impurities and the subsequent loss of resolution and gain are considered. Temporal observations of VEL X-1, showing the 290s periodicity, and SCO X-1, indicating rapid intensity variations, and spectral analyses of SCO X-1 are presented. More recent improvements to the telescope system are also described. Following the discovery of periodic radio flaring coincident with sharp X-ray cutoffs from CIR X-1 a radio survey of 98 well determined X-ray source positions at 14.7 GHz (˜í¬™=2cm) was undertaken using the Parkes 64 m radio-telescope. Twelve radio counterparts, eight of which are new, were detected and a further 81 upper limits were obtained. Searches for variable radio emission correlated with X-ray events from X-ray burst sources, as part of a world-wide 'Burst Watch', gave a null result but enabled upper limits to the radio burst flux to be established. Results from monitoring a complete flare of CIR X-1 showed a complex triple peaked structure at ˜í¬™ = 2 cm. Observations carried out at 5 GHz (˜í¬™=6cm) were combined with other published results to deduce a rate of decrease for the orbital period of CIR X-1. The implications of these observation are discussed with particular reference to the recent eccentric orbit, luminosity-driven shock model for radio emission from CIR X-1. The significance of the other radio counterparts and selected upper limit results are also considered.