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

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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 K α 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 K α line. The ratio of the Compton-shoulder flux to that of the Fe K α core exhibits orbital-phase variability, reaching a maximum of ∼10% around orbital phase ϕ orb ≃ 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 K α 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.

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