LSI +61 303 is one of the few X-ray binaries with Be star companion from which both radio and high-energy gamma-ray emission have been observed. We present XMM-Newton and INTEGRAL observations which reveal variability of the X-ray spectral index of the system. The X-ray spectrum is hard (photon index ~ 1.5) during the orbital phases of both high and low X-ray flux. However, the spectrum softens at the moment of transition from high to low X-ray state. The spectrum of the system in the hard X-ray band does not reveal the presence of a cut-off (or, at least a spectral break) at 10-60 keV energies, expected if the compact object is an accreting neutron star. The observed spectrum and spectral variability can be explained if the compact object in the system is a rotation powered pulsar.
@article{arxiv.astro-ph/0606070,
title = {INTEGRAL and XMM-Newton observations of LSI +61 303},
author = {M. Chernyakova and A. Neronov and R. Walter},
journal= {arXiv preprint arXiv:astro-ph/0606070},
year = {2008}
}