Spectral and temporal properties of the supergiant fast X-ray transient IGR J18483–0311 observed by INTEGRAL

Context. IGR J18483−0311 is a supergiant fast X-ray transient whose compact object is located in a wide (18.5 d) and eccentric (e ~ 0.4) orbit, which shows sporadic outbursts that reach X-ray luminosities of ~1036 erg s-1. Aims. We investigated the timing properties of IGR J18483−0311 and studied the spectra during bright outbursts by fitting physical models based on thermal and bulk Comptonization processes for accreting compact objects. Methods. We analysed archival INTEGRAL data collected in the period 2003–2010, focusing on the observations with IGR J18483−0311 in outburst. We searched for pulsations in the INTEGRAL light curves of each outburst. We took advantage of the broadband observing capability of INTEGRAL for the spectral analysis. Results. We observed 15 outbursts, seven of which we report here for the first time. This data analysis almost doubles the statistics of flares of this binary system detected by INTEGRAL. A refined timing analysis did not reveal a significant periodicity in the INTEGRAL observation where a ~21 s pulsation was previously detected. Neither did we find evidence for pulsations in the X-ray light curve of an archival XMM-Newton observation of IGR J18483−0311. In the light of these results the nature of the compact object in IGR J18483−0311 is unclear. The broadband X-ray spectrum of IGR J18483−0311 in outburst is well fitted by a thermal and bulk Comptonization model of blackbody seed photons by the infalling material in the accretion column of a neutron star. We also obtained a new measurement of the orbital period using the Swift/BAT light curve