IGRJ16479-4514: the first eclipsing supergiant fast X-ray transient?

Abstract

Supergiant fast X-ray transients (SFXTs) are a new class of high-mass X-ray binaries recently discovered with INTEGRAL. Hours-long outbursts from these sources have been observed on numerous occasions at luminosities of ~10³⁶-10³⁷ergs^-1, whereas their low-level activity at ~10³²-10³⁴ergs^-1 has not been deeply investigated yet due to the paucity of long pointed observations with high-sensitivity X-ray telescopes. Here, we report on the first long (~32 ks) pointed XMM-Newton observation of IGRJ16479-4514, a member of this new class. This observation was carried out in 2008 March, shortly after an outburst from this source, with the main goal of investigating its low-level emission and physical mechanisms that drive the source activity. Results from the timing, spectral and spatial analysis of the EPIC-PN XMM-Newton observation show that the X-ray source IGRJ16479-4514 underwent an episode of sudden obscuration, possibly an X-ray eclipse by the supergiant companion. We also found evidence for a soft X-ray extended halo around the source that is most readily interpreted as due to scattering by dust along the line of sight to IGRJ16479-4514. We discuss this result in the context of the gated accretion scenarios that have been proposed to interpret the behaviour of SFXT.