2007A&A...468L..21S

The transient hard X-ray source IGR J11321-5311 was discovered by INTEGRAL on June 2005, during observations of the Crux spiral arm. To date, this is the only detection of the source to be reported by any X/γ-ray mission. To characterize the behaviour and hence the nature of the source through temporal and spectral IBIS analysis. Detailed spectral and temporal analysis has been performed using standard INTEGRAL software OSA v.5.1. To date, IGR J11321-5311 has been detected only once. It was active for ∼3.5h, a short and bright flare lasting ∼1.5h is evident in the IBIS light curve. It reached a peak flux of ∼80 mCrab or 2.2x10^–9erg/cm2/s (20-300keV), corresponding to a peak luminosity of ∼1.1x10³⁷erg/s (assuming a distance of 6.5kpc). During the outburst, the source was detected with a significance of ∼18σ (20-300keV) and ∼8σ (100-300keV). The spectrum of the total outburst activity (17-300keV) is best fitted by the sum of a power law (Γ=0.55±0.18) plus a black body (kT=1.0^+0.2_–0.3keV), with no evidence for a break up to 300 keV. A spectral analysis at Science Window level revealed an evident hardening of the spectrum through the outburst. The IBIS data were searched for pulsations with no positive result. The X-ray spectral shape and the flaring behaviour favour the hypothesis that IGR J11321-5311 is an Anomalous X-ray Pulsar, though a different nature can not be firmly rejected at the present stage.