Radio Stars and X-ray Sources

Abstract

Limits are reported on x-ray emission from known radio stars. The results are of interest because of the possible association between x-ray binaries and radio star binaries, and because measurements of x-ray fluxes can help determine the source of the radio emission. The principal results are shown tabulated, and were obtained from Uhuru data. None of the radio stars was detected as an x-ray source. A typical upper limit to the x-ray flux (2 to 6 keV) from one of the radio stars is 3 x 10/sup -11/erg//cm/ sup 2//sec., which is about 3 x 10/sup -3/mfu, or 0.3% of the average x-ray flux from Cyg X-1. The seven radio stars for which results are given show comparable radio fluxes (1 to 10 mfu) but except for HDE226868 none are strong x-ray sources. This suggests that there are two types of radio binary stars, one which is a strong x-ray source and the other not. Radio stars that are also strong x-ray emitters may contain an additional component in the binary system, for example, a black hole or a large magnetic field, or they may simply be hotter versions of the same basic system. Mechanisms are discussed. (UK)