Spectral evolution of the supergiant HMXB IGR J16320–4751 along its orbit using

Context. The INTEGRAL satellite has revealed a previously hidden population of absorbed high-mass X-ray binaries (HMXBs) hosting supergiant stars. Among them, IGR J16320–4751 is a classical system intrinsically obscured by its environment, with a column density of ∼1023 cm−2, more than an order of magnitude higher than the interstellar absorption along the line of sight. It is composed of a neutron star rotating with a spin period of ∼1300 s, accreting matter from the stellar wind of an O8I supergiant star, with an orbital period of ∼9 days. Aims. We investigated the geometrical and physical parameters of both components of the binary system IGR J16320–4751. Since in systems of this type the compact object is usually embedded in the dense and powerful wind of an OB supergiant companion, our main goal here was to study the dependence of the X-ray emission and column density along the full orbit of the neutron star around the supergiant star. Methods. We analyzed all existing archival XMM-Newton and Swift/BAT observations collected between 2003 and 2008, performing a detailed temporal and spectral analysis of the X-ray emission of the source. We then fitted the parameters derived in our study, using a simple model of a neutron star orbiting a supergiant star. Results. The XMM-Newton light curves of IGR J16320–4751 display high-variability and flaring activity in X-rays on several timescales, with a clear spin period modulation of ∼1300 s. In one observation we detected two short and bright flares where the flux increased by a factor of ∼10 for ∼300 s, with similar behavior in the soft and hard X-ray bands. By inspecting the 4500-day light curves of the full Swift/BAT data, we derived a refined period of 8.99 ± 0.01 days, consistent with previous results. The XMM-Newton spectra are characterized by a highly absorbed continuum and an Fe absorption edge at ∼7 keV. We fitted the continuum with a thermally comptonized COMPT