IGR J16318-4848: 7 years of INTEGRAL observations

Abstract

Since the discovery of IGR J16318−4848 in 2003 January, INTEGRAL has accumulated more than 5.8 Ms in IBIS/ISGRI. We present the first extensive analysis of the archival INTEGRAL data (IBIS/ISGRI, and JEM-X when available) for this source, together with the observations carried out by XMM-Newton (twice in 2003, and twice in 2004) and Suzaku (2006). The source is very variable in the long-term, with periods of low activity, where the source is almost not detected, and flares with a luminosity ∼ 10 times greater than its average value (5.4 cts/s). IGR J16318−4848 is a HMXB containing a sgB[e] star and a compact object (most probably a neutron star) deeply embedded in the stellar wind of the mass donor. The variability of the source (also in the short-term) can be ascribed to the wind of the optical star being very clumpy. We study the variation of the spectral parameters in time scales of INTEGRAL revolutions. The photoelectric absorption is, with NH around 10²⁴ cm⁻² , unusually high. During brighter phases the strong K-alpha iron line known from XMM-Newton and Suzaku observations is also detectable with the JEM-X instrument.