Cyclotron line emission from binary X-ray sources

Abstract

X-ray spectral data concerning an electron-cyclotron emission line centered at 58 keV in the spectrum of Her X-1 are reviewed. It is shown that the observed spectral shape and intensity constrain thermal X-ray production to annular hot spots at the neutron-star surface around the magnetic poles and that extended radiative shocks of the type described by Inoue (1975) and by Basko and Sunyaev (1976) may be ruled out for Her X-1. Evidence is discussed which indicates that magnetic-field variations of about 2 to 3 trillion gauss may occur in the hot spots over short time periods. Possible candidates among X-ray binaries for the observation of X-ray cyclotron emission are briefly considered.