出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：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 G ≃ 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. In this case the recently found X-ray spectral variability
of the system on the several kiloseconds time scale can be explained by the clumpy structure of
the Be star disk.
