High energy X-ray spectrum of Her X-1
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.
- Publication:
-
Nature
- Pub Date:
- September 1978
- DOI:
- Bibcode:
- 1978Natur.275..195D
- Keywords:
-
- Pulsars;
- Spaceborne Astronomy;
- Stellar Spectra;
- X Ray Spectra;
- X Ray Stars;
- Background Radiation;
- Line Spectra;
- Oso-8;
- Satellite-Borne Instruments;
- Astrophysics