IGR J11215-5952: a hard X-ray transient displaying recurrent outbursts

Abstract

The hard X-ray source IGRJ11215-5952 has been discovered with INTEGRAL during a short outburst in 2005 and proposed as a new member of the class of supergiant fast X-ray transients. We analysed INTEGRAL public observations of the source field in order to search for previous outbursts from this transient, not reported in literature.Our results are based on a systematic re-analysis of INTEGRAL archival observations, using the latest analysis software and instrument calibrations. We report the discovery of two previously unnoticed outbursts, spaced by intervals of ~330 days, that occurred in July 2003 and May 2004. The 5-100keV spectrum is well described by a cut-off power law, with a photon index of 0.5, and a cut-off energy ~15-20keV, typical of High Mass X-ray Binaries hosting a neutron star. A 5-100keV luminosity of 3E36 erg/s has been derived (assuming 6.2kpc, the distance of the likely optical counterpart). The 5-100keV spectral properties, the recurrent nature of the outbursts,together with the reduced error region containing the blue supergiant star HD306414,support the hypothesis that IGRJ11215-5952 is a member of the class of the Supergiant Fast X-ray Transients.