X-ray observations of the peculiar Be star LSI +61 303

Abstract

We present the results of a ROSAT Position Sensitive Proportional Counter observation of the variable radio star \ls. The source has a power law spectrum with photon index 1.1 +/- 0.3 and a luminosity of 5.9 x 10^{33} erg/s in the 0.1 -2.4 keV range. Variability on a timescale of days is clearly visible in the ROSAT data, but no periodic pulsations have been detected. The low X--ray luminosity is difficult to explain in the context of the models involving super Eddington accretion which have been proposed to account for the non thermal radio outbursts. Though the weak X--ray flux is marginally compatible with the levels expected from normal B and Be star winds, the variability and the rather hard spectrum are more suggestive of non thermal emission. This might originate in a shocked region produced by a young pulsar in orbit around the Be star.