SIMBAD references

We have observed the Galactic center hard X-ray pulsar GX 1+4 on 1993 December 11, in the energy range of 20-100keV with a balloon-borne Xenon filled Multi-cell Proportional Counter (XMPC) telescope. The source was detected in a bright state, the average observed source count rate being 10.1±0.2s^–1 per detector. X-ray pulsations with a period of 121.0±0.4s were detected in the source at a very high significance level. This, compared with the BATSE observations, gives a spin down rate of P=1.6±1.4s/yr. The pulse fraction in the hard X-ray range is low (35%), and the observed spectrum is very hard (power law energy index 0.54±0.18). The observed source luminosity in the 20-100keV range is 7.9±0.3x10³⁷erg/s. These properties are similar to those seen during the high luminosity spin up state of early 1970s and suggest that the source should revert back to a spin-up episode.