Reanalysis of the 1973 outburst of the X-ray transient V0332+53

The known X-ray transient pulsar V0332+53 underwent a major outburst June-September 1973. The event reached a maximum average intensity in the 3-12-keV energy band of 1.6 times that of the Crab and exhibited variations up to 2.5 times that standard value on time scales of minutes. The 4.37-sec pulse period was seen during this outburst and implies a secular spin-period change of less than 4 x 10 to the -13th/sec between this event and the next detection of the pulse period in 1983 by Exosat. The 100-day outburst exhibits a modulation at the 34-day orbital period. As a result, an improved orbital period of either 34.38 + or - 0.02 or 34.07 + or - 0.02 days can be suggested for this source. Furthermore, this type of modulation implies that accretion from an evolving circumstellar envelope of the Be-star companion can account for the behavior of this transient.