Observations and modelling of the hard X-ray emission from GX 1 + 4

The X-ray pulsar GX 1+4 was observed during a balloon flight from Alice Springs, Australia on 1986 November 20. Significant flux was detected over the full energy range of the detector (15-114 keV). The spectrum is very hard with a power-law photon index of 1.85±0.25. The intensity at 30 keV is (5.1±0.5)×10 −4 cm −2 s −1 keV −1 , a factor of ∼3 less than typical during the 1970s but orders of magnitude greater than during satellite measurements in 1984 and in early 1987, a few months after the flight. The pulse profiles below ∼75 keV are very broad and possibly double-peaked

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