ar X iv : a st ro - p h / 02 07 10 2 v 1 4 J ul 2 00 2 A XMM - Newton observation during the 2000 outburst of SAX J 1808 . 4 – 3658

A XMM-Newton observation is presented 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 × 10 erg s. 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 with a combination of a thermal (either a black-body or an atmosphere model) and a power-law component. During a XMM-Newton observation taken approximately one year later, the source was in quiescence and its luminosity was a factor of ∼4 lower and the source spectrum during the 2000 outburst was softer than its quiescent spectrum. The obtained results are discussed in the context of the 2000 outburst of SAX J1808.4–3658 and the quiescent properties of the source. Subject headings: accretion, accretion disks — stars: individual (SAX J1808.4–3658) — stars: neutron