First Look at the High-resolution X-Ray Spectra in the Highly Absorbed High-mass X-Ray Binary IGR J16318−4848 with Chandra

Abstract

We present a comprehensive analysis of the X-ray spectrum of the highly obscured high-mass X-ray binary IGR J16318−4848 based on ∼250 ks Chandra/HETGS observations covering different orbital phases. We detected a strong narrow Fe Kα emission line and interpret our finding as the iron line originating in the stellar wind close to the compact object. We tentatively identify a Compton shoulder associated with the Fe Kα line. The ratio of the Compton-shoulder flux to that of the Fe Kα core exhibits orbital-phase variability, reaching a maximum of ∼10% around orbital phase ϕorb ≃ 0.33. In addition, we do not detect ionized lines, implying that the plasma in the system is predominantly cold. We preliminarily report that the Fe Kα line centroid exhibits an orbital modulation with an amplitude of 167 ± 32 km s−1, adopting the best-known circular orbit in the source. This study presents the first detailed view of the high-resolution X-ray spectra of IGR J16318−4848 across different orbital phases, providing timely context for the newly taken XRISM observations of the source.