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

Abstract

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.