The 1973 X-ray outburst of 4U1145-61

This paper describes observations of X-ray outbursts in 1973, carried out by the Vela 5B spacecraft, which indicated the presence of the transient source 4U1145-61. This source was later found to be two hard X-ray pulsars separated by about 20 arcmin. The two periods are quite similar: 292 sec for the 2S1145-619 pulsar (still known as 4U1145-61) and 297 sec for the IE1145.1-6141. The time history of the March-May 1973 X-ray outburst of 4U1145-619, as given by Vela 3-12 keV data at 56-hr intervals, is presented as well as the Fourier power spectrum of 4U1145-619 observations for April 5, 1973. The results of the outburst analyses are discussed.