Hard X-ray pulse profile of GX1+4

Abstract

We have observed the Galactic center X-ray pulsar GX 1+4 using a balloon-borne hard X-ray telescope. Hard X-ray pulse profiles and spectral parameters were obtained on two occasions; during the high state of December 1993 when the hard X-ray pulse fraction was very low and in March 1995 when there was an indication of the pulse period variation sign reversal. We find significant differences in the pulse shape on these two occasions: the hard X-ray pulse profile changed from a smooth sinusoidal to a double peak structure. The details of the observations are presented and the implications of these results on the accretion process near the compact object are outlined.