1. Where is the supervirial hot gas? I: a pilot study with sightlines to Galactic X-ray binaries.
- Author
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Lara-DI, Armando, Krongold, Yair, Mathur, Smita, Roy, Manami, McClain, Rebecca L, Das, Sanskriti, and Gupta, Anjali
- Subjects
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X-ray binaries , *INTERSTELLAR medium , *GALACTIC evolution , *MILKY Way , *PILOT projects - Abstract
Hot, |$\log (T/\mathrm{K})$| |$\sim$| 7.5, gas was recently discovered in the Milky Way in extragalactic sightlines. In order to determine its location, here we present sightlines to Galactic X-ray binaries (XRBs) passing through the Interstellar Medium (ISM). In this pilot study, we investigate absorption features of S |$_{\mathrm{XVI}}$| , Si |$_{\mathrm{XIV}}$| , and Ne |$_{\mathrm{X}}$| in the spectra of three XRBs, namely 4U 1735–44, 4U 1820–30, and Cyg X-2, using Chandra High Energy Transmission Grating archival observations. We do not detect any of these lines. We determine the 2 |$\sigma$| upper limit for the equivalent widths of the undetected absorption lines and the column densities of the corresponding ions. We note that the 2 |$\sigma$| upper limits for S |$_{\mathrm{XVI}}$| K |$\alpha$| and Si |$_{\mathrm{XIV}}$| K |$\alpha$| are an order of magnitude smaller than those previously detected in the extragalactic sightlines. Our finding suggests that if any gas at |$\log (T/\mathrm{K})$| |$\gt\ 7$| is present in the Galactic ISM, it is unlikely to be ubiquitous. This is an important result because it implies that S |$_{\mathrm{XVI}}$| , Si |$_{\mathrm{XIV}}$| , and Ne |$_{\mathrm{X}}$| absorption detected in extragalactic sightlines is not from the ISM, but is likely from a hot gas phase in the extraplanar region beyond the ISM or in the extended Circumgalactic Medium. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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