Observations of X-ray bursts from the vicinity of 3U 1727-33

Some x-ray observations of the sky region near 3U 1727-33 made in March 1976 using an Ariel V experiment are described. The equipment included a multiwire collimated proportional counter, and the field of view included the positions of 3U 1727-33, MX 1716-30, and two recently discovered burst sources, MXB 1730-335 and MXB 1728-34. Observations were made with a time resolution of 32.24 and 0.5 sec in the 2 to 7 keV energy band. During a total of 17 hours actual observing time 17 bursts were recorded, the strengths of which are listed. Most of the bursts lasted only a few seconds, but some persisted for up to 20 sec. The longer lasting bursts showed clear evidence for satellite spin modulation, and large and small bursts appeared to originate from the same source. The bursts observed came in groups within which the pulse separation remained constant. The bursts were thought to originate from MXB 1730-335, and their sequences maintained their phase and period for several cycles; thereafter they were subject to abrupt change in either phase period. Longer lasting bursts could be followed by relatively quiescent intervals. The abrupt changes in phase and period suggest that the bursts trains were not produced by a rigid dynamical system such as a rotating star or orbiting stars, but that they represented a characteristic oscillation period in the x-ray production mechanism or orbital motion in some non-rigid system such as an accretion disk. (U.K.)