Abstract
OBSERVATIONS of Her X–1 taken during the on-state of its 35-d cycle1 between 31 August and 12 September 1977 with the high-energy X-ray detector on board OSO 8 are reported here. A detailed analysis of the time-variable background spectrum suggests that the line features observed in our uncorrected time-averaged spectrum and those previously reported at 25, 60 and 135 keV can be caused by a ∼1% change in detector gain. After correcting for this effect, a 3-σ upper limit of 4×10−3 photons cm−2 s−1 is obtained on the line flux at 60 keV in the time-averaged spectrum, a flux significantly lower than that observed by Coe et al.2 6 months earlier. A 3-σ upper limit of 2×10−3 photon cm−2 s−1 obtained for our pulsed spectrum at the same energy is higher than, and hence consistent with, the positive result reported by Trümper3,4 from a balloon flight during the same time interval.
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DENNIS, B., MAURER, G., CUTLER, E. et al. High energy X-ray spectrum of Her X-1. Nature 275, 195–197 (1978). https://doi.org/10.1038/275195a0
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DOI: https://doi.org/10.1038/275195a0
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