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Hercules X-1 hard X-ray pulsations observed from HEAO 1
Gruber, D. E.; Matteson, J. L.; Nolan, P. L.; Knight, F. K.; Baity, W. A.; Rothschild, R. E.; Peterson, L. E.; Hoffman, J. A.; Scheepmaker, A.; Wheaton, W. A.; Primini, F. A.; Levine, A. M.; Lewin, W. H. G.
AA(California, University, La Jolla, Calif.), AB(California, University, La Jolla, Calif.), AC(California, University, La Jolla, Calif.), AD(California, University, La Jolla, Calif.), AE(California, University, La Jolla, Calif.), AF(California, University, La Jolla, Calif.), AG(California, University, La Jolla, Calif.), AH(MIT, Cambridge, Mass.), AI(MIT, Cambridge, Mass.), AJ(MIT, Cambridge, Mass.)
Astrophysical Journal, Part 2 - Letters to the Editor, vol. 240, Sept. 15, 1980, p. L127-L131. (ApJL Homepage)
Publication Date:
NASA/STI Keywords:
Binary Stars, Heao 1, Light Curve, Stellar Spectra, Variable Stars, X Ray Sources, Earth Magnetosphere, Energy Spectra, Neutron Stars, Pulse Duration, Spectral Line Width, Spectrum Analysis
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The 1.24-sec pulsations of Her X-1 in the energy range 13-75 keV have been analyzed in data obtained from the UCSD/MIT experiment on HEAO 1 during observations of the source on three dates in February 1978 and three in August 1978. Observational results are (1) the main pulse broadens somewhat with increasing energy; (2) the pulsation light curve undergoes pronounced changes at the leading edge of the main pulse from day to day; (3) spectral hardening within the main pulse is confirmed; (4) a 40-60 keV spectral feature in the spectrum is confirmed; (5) this feature is resolved, the pulse width broadening is greater than 20%, and its centroid varies with pulsation phase; and (6) the 13-75 keV spectrum does not noticeably vary from day to day, except for an overall intensity factor. Some implications of these results for the prevailing models of Her X-1 and the HZ Her-Her X-1 system are briefly discussed.

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