THE INTEGRAL SOURCE IGR J16328–4726: A HIGH-MASS X-RAY BINARY FROM THE BEPPOSAX ERA

We report on temporal and spectral analysis of the INTEGRAL fast transient candidate IGR J16328–4726 observed with BeppoSAX in 1998 and more recently with INTEGRAL. The MECS X-ray data show a frequent microactivity typical of the intermediate state of supergiant fast X-ray transients and a weak flare with a duration of ~4.6 ks. The X-ray emission in the 1.5-10 keV energy range is well described through the different time intervals by an absorbed power-law model. Comparing spectra from the lower emission level up to the peak of the flare, we note that while the power-law photon index was constant (~2), the absorption column density varied by a factor of up to ~6-7, reaching a value of ~2 × 1023 cm–2 at the peak of the flare. Analysis of the long-term INTEGRAL/IBIS light curve confirms and refines the proposed ~10.07 day period, and the derived ephemeris places the BeppoSAX observations away from periastron. Using the near- and the mid-IR available observations, we constructed a spectral infrared distribution for the counterpart of IGR J16328–4726, allowing us to identify its counterpart as a high-mass OB type star and to classify this source as a firm HMXB. Following the standard clumpy wind theory, we estimated the mass and the radius of the clump responsible for the flare. The obtained values of M cl 4 × 1022g and Rcl 4.4 × 106 km are in agreement with expected values from theoretical predictions.