Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1977
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1977apj...214..879b&link_type=abstract
Astrophysical Journal, Part 1, vol. 214, June 15, 1977, p. 879-884.
Astronomy and Astrophysics
Astrophysics
69
Binary Stars, Satellite-Borne Instruments, Spectrum Analysis, Stellar Spectra, X Ray Spectra, Cut-Off, Stellar Mass Accretion, X Ray Scattering, X Ray Sources
Scientific paper
X-ray spectra for Her X-1 are presented for times before, during, and after a turn-on in the 35 day on-off cycle, as well as during an anomalous dip in the X-ray intensity. All four spectra are well represented by a power law of number index 0.9 with a high-energy cutoff near 20 keV. However, the column density of cold matter along the line of sight as estimated by the low-energy cutoff varies substantially among the four intervals. The low level flux present prior to turn-on was not seen to pulse and showed very little low-energy absorption, in contrast to the X-rays observed during the turn-on and the anomalous dip. It seems likely that the pre-turn-on flux is composed of X-rays scattered into the line of sight by material away from the accretion disk. An accurate determination of the pulsation period for Her X-1 during 1975 August finds the period has decreased to 1.2378065 plus or minus 0.0000001 s.
Becker Robert H.
Boldt Elihu A.
Holt Stephen S.
Pravdo Steven Howard
Rothschild Richard E.
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