1996A&A...305..817T

Coordinated X-ray and two-frequency radio observations were carried out over one cycle of the periodic, radio-emitting binary system LSI+61 303, using the ROSAT and VLA observatories. An X-ray outburst, with a duration of about 10 days, was detected. Both the radio and X-ray flux densities varied by a factor of 10, with the X-ray peak occurring at phase 0.5 and the radio peak at phase 0.95. The range of phase of high X-ray emission matches the phase interval during which the source is, on average, active at radio. Timing analysis of the X-ray data failed to detect pulsed emission in the period range of 1.5 milliseconds to 3000 seconds. We discuss a model in which the X-ray emission is produced in hot circumstellar gas shocked by the expanding plasmon of relativistic electrons that is responsible for the radio outburst. With the known parameters of the circumstellar gas, the binary system and the radio plasmon, such a model is able to reproduce both the luminosity and spectral properties of the keV X-rays, and the timing of the X-ray emission relative to the radio outburst. Inverse-Compton scattering of stellar photons off relativistic particles in the expanding plasmon can account for the γ-ray luminosity of LSI+61 303 and the low ratio of X-ray to γ-ray emission.