The variability of several galactic X-ray sources

The MSSL/UCL X-ray detectors on both the Copernicus and Ariel V satellites have been used to investigate the variability of certain Galactic X-ray sources. A search for periodic modulations on a time scale of minutes in the X-ray flux from these sources is reported. Evidence for the positive detection of regular pulsations in several cases including 3U0352+30 (X Per), GX 17+2, GX 1+4 and 3U1727-33 as well as measurements on some of the other previously known pulsators are given. Additional observations of the source 3U0352+30 show that as well as a 13.9 minute modulation, it also exhibits both long and short timescale intensity and spectral variability. In particular evidence for a second modulation of the X-ray flux at a period of 22.4 hours is presented. The implications of these X-ray results on the proposed optical counterpart X Per, its reported 580 day period, and possible models for this system are discussed. Observations of Sco X-1 are reported where X-ray data with improved spectral and temporal resolution has been obtained with, in some cases, simultaneous optical coverage. These data both confirm and clarify earlier spectral work on this source. Evidence is found for a one minute time delay between optical and X-ray flares. Measurements on the variability of GX 17+2 are presented. The behaviour of this source is found to be similar to that of Sco X-1 in that intensity variability correlates with changes in the source temperature. The implications of this result to the Sco X-1 sources in general is discussed. Finally both the instrumentation and techniques used in the search for variability from X-ray sources are described.