An XMM-Newton Observation during the 2000 Outburst of SAX J1808.4-3658

Abstract

I present an XMM-Newton observation of the accretion-driven millisecond X-ray pulsar SAX J1808.4-3658 during its 2000 outburst. The source was conclusively detected, albeit at a level of only ~2×10³² ergs s^-1. The source spectrum could be fitted with a power-law model (with a photon index of ~2.2), a neutron star atmosphere model (with a temperature of ~0.2 keV), or a combination of a thermal (either a blackbody or an atmosphere model) and a power-law component. During an XMM-Newton observation taken approximately 1 yr later, the source was in quiescence, and its luminosity was a factor of ~4 lower. It is possible that the source spectrum during the 2000 outburst was softer than its quiescent 2001 spectrum; however, the statistics of the data do not allow a firm conclusion. The results obtained are discussed in the context of the 2000 outburst of SAX J1808.4-3658 and the quiescent properties of the source.