A low luminosity state in the massive X-ray binary SAX J0635+0533

Abstract

The X-ray pulsar SAX J0635+0533 was repeatedly observed with the XMM-Newton satellite in 2003-2004. The precise localization provided by these observations confirms the association of SAX J0635+0533 with a Be star. The source was found, for the first time, in a low-intensity state, a factor ∼ 30 lower than that seen in all previous observations. The spectrum, well fitted by an absorbed power law with photon index ∼ 1.7 and NH = 1.2 × 1022 cm-2, was compatible with that of the high state. The low flux did not allow the detection of the pulsations at 33.8 ms seen in BeppoSAX and RXTE data. In view of the low luminosity observed in 2003-2004, we reconsider the peculiarities of this source in both the accretion and rotation-powered scenarios. © 2009 ESO.