RADIO-EMITTING X-RAY BINARIES

Abstract

ABSTRACT Radio emission in X-ray binaries is thought to be synchrotron radiation from relativistic electrons in hot ionized clouds ( plasmons). When such plasmons are ejected, probably as a result of transitory supercritical accretion events, a radio outburst takes place. In the present PhD work, different models are developed for explaining these radio outbursts in terms of relativistic particle injection into an expanding radio source. The models are applied to several X-ray binary systems for which multi-frequency radio observations are available in the literature. In particular, the radio outbursts of the 26.5~d radio periodic X-ray binary LSI+61 degree 303 are interpreted in this way, obtaining physical parameters which have been confirmed later by independent VLBI observations. Also, due to the special astrophysical interest of this object, an extended observational and theoretical study has been performed. New radio, infrared and optical observations are presented. In particular, an infrared modulation is reported, with amplitude ~0m.2 and period similar to that of radio outbursts. The light curves obtained are interpreted using an eclipse-attenuation model, which seems to be consistent with a highly eccentric orbit. The possible implication of such an eccentric orbit in the delay observed between X-ray and radio outbursts is also discussed. Finally, the results of a search for new radio emitting X-ray binaries are presented. There are two main findings in this part of the work. First, the radio counterpart of the hard X-ray sources GRS1758-258 and GRS1915+105 has been discovered with the VLA. The high energy spectrum of these objects is consistent with being X-ray binary systems whose compact companion is a black hole. Second, I-band CCD observations have allowed the identification of an optical counterpart for several galactic plane radio variables taken from the GT catalogue. This is a necessary step in order to determine, from future spectroscopic work, if some of these GT objects are actually or not galactic binary systems.