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

Context: .The hard X-ray source IGR J11215-5952 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.
Aims: .We analysed INTEGRAL public observations of the source field in order to search for previous outbursts from this transient, not reported in literature.
Methods: .Our results are based on a systematic re-analysis of INTEGRAL archival observations, using the latest analysis software and instrument calibrations.
Results: .We report the discovery of two previously unnoticed outbursts, spaced by intervals of ~330 days, that occurred in July 2003 and May 2004. The 5-100 keV spectrum of IGR J11215-5952 is well described by a cut-off power law, with a photon index of ~0.5, and a cut-off energy ~15-20 keV, typical of High Mass X-ray Binaries hosting a neutron star. A 5-100 keV luminosity of ∼3×10³⁶ erg s^-1 has been derived (assuming 6.2 kpc, the distance of the likely optical counterpart).
Conclusions: .The 5-100 keV spectral properties, the recurrent nature of the outbursts, together with the reduced error region containing the blue supergiant star HD 306414, support the hypothesis that IGR J11215-5952 is a member of the class of the Supergiant Fast X-ray Transients.