Suzaku Observation of Igr J16318-4848

Abstract

IGR J16318-4848 is the first example of a new class of highly absorbed X-ray binaries that has been discovered by INTEGRAL. We analyzed the first Suzaku observation of this source (2006 August 14--17), and obtained a spectrum that can be well described by an absorption model (TBabs) and a cutoff powerlaw, plus the Gaussians for the emission lines of Fe {Kα }, Fe {Kβ } and Ni {Kα }. The spectrum also shows a soft excess below 5 keV, which is probably due to a contaminating source (Ibarra et al. 2007). The flux curve varies significantly in hours; however the source remains always in a hard state, with very slight changes on the hardness ratio. Despite the large N_H we obtain in the fit to our model, no Compton shoulder is seen in the lines, arguing for a non-spherical and inhomogeneous absorber. The fit requires a slight overabundance of iron with respect to the ISM values of Wilms et al. (2000), as one would expect for an evolved star. Furthermore, the flux ratio of Fe and Ni also points towards a Ni overabundance by a factor of ∼ 2 with respect to Fe. The spectral characteristics of the source suggest a neutron star as the compact object in the binary system.