XRISM insights for interstellar sulfur

Abstract The X-ray Imaging Spectroscopy Mission (XRISM) provides the best spectral resolution with which to study sulfur (S) K-shell photoabsorption features from the interstellar medium (ISM). For the first time, we demonstrate the high-signal detection of interstellar atomic S ii K-beta absorption in the spectrum of X-ray binaries (XRBs) 4U 1630-472 and GX 340$+$0. The persistence of this feature across multiple instruments, targets, and flux states implies that it is interstellar in nature. We measure the S ii K$\beta$ line centroid at $2470.8 \pm 1.1$ eV after including systematic uncertainties. We also find that the most recently published high-resolution S ii absorption template requires a systematic energy scale shift of $+7\!-\!8$ eV, which is comparable to the level of disagreement among various atomic modeling procedures. The XRISM 300 ks observation of GX 340$+$0 provides unprecedented signal-to-noise in the S K region, and we find evidence of residual absorption from solid S in the spectra of GX 340$+$0. Absorption templates from three Fe-S compounds, troilite (FeS), pyrrhotite (Fe$_7$S$_8$) and pyrite (FeS$_2$), provide equally good fits to the residuals. Even though we are not able to distinguish among these three compounds, they provide equal estimates for the abundance of S locked in dust grains. Having accounted for both the gaseous and solid S in the GX 340$+$0 sightline provides us with a direct measurement of S depletion, which is $40{\%} \pm 15\%$. Our depletion measurement provides an upper limit to the fraction of interstellar Fe bound in Fe-S compounds of ${<}25\%$, which is consistent with prior studies of Fe-S compounds via Fe L-shell absorption. Both XRBs in this study are at a distance of approximately 11 kpc and on the opposite side of the Galactic disk, suggesting that this value could represent the average S depletion of the Milky Way when integrated across all phases of the ISM.

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Publication Details

Journal
Publications of the Astronomical Society of Japan
Published
2025-06-27
DOI
https://doi.org/10.1093/pasj/psaf068
Citations
2
Primary Topic
High-pressure geophysics and materials
Type
article
Field-Weighted Citation Impact
3.73

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article

XRISM insights for interstellar sulfur

Lía Corrales, M. Shidatsu, D. L. Moutard, María Díaz Trigo et al.
2 citations
Publications of the Astronomical Society of Japan
High-pressure geophysics and materials
3.73
article

XRISM insights for interstellar sulfur

Lía Corrales, M. Shidatsu, D. L. Moutard, María Díaz Trigo, J. M. Mïller, S. T. Zeegers, I. Psaradaki, Liyi Gu, Priyanka Chakraborty, Randall K. Smith, Ralf Ballhausen, Misaki Mizumoto, R. M. Ludlam, Takao Nakagawa, E. Costantini, H. Takahashi, S. Yamada, Caroline A. Kilbourne
article en
2 citations

Abstract

Abstract The X-ray Imaging Spectroscopy Mission (XRISM) provides the best spectral resolution with which to study sulfur (S) K-shell photoabsorption features from the interstellar medium (ISM). For the first time, we demonstrate the high-signal detection of interstellar atomic S ii K-beta absorption in the spectrum of X-ray binaries (XRBs) 4U 1630-472 and GX 340$+$0. The persistence of this feature across multiple instruments, targets, and flux states implies that it is interstellar in nature. We measure the S ii K$\beta$ line centroid at $2470.8 \pm 1.1$ eV after including systematic uncertainties. We also find that the most recently published high-resolution S ii absorption template requires a systematic energy scale shift of $+7\!-\!8$ eV, which is comparable to the level of disagreement among various atomic modeling procedures. The XRISM 300 ks observation of GX 340$+$0 provides unprecedented signal-to-noise in the S K region, and we find evidence of residual absorption from solid S in the spectra of GX 340$+$0. Absorption templates from three Fe-S compounds, troilite (FeS), pyrrhotite (Fe$_7$S$_8$) and pyrite (FeS$_2$), provide equally good fits to the residuals. Even though we are not able to distinguish among these three compounds, they provide equal estimates for the abundance of S locked in dust grains. Having accounted for both the gaseous and solid S in the GX 340$+$0 sightline provides us with a direct measurement of S depletion, which is $40{\%} \pm 15\%$. Our depletion measurement provides an upper limit to the fraction of interstellar Fe bound in Fe-S compounds of ${<}25\%$, which is consistent with prior studies of Fe-S compounds via Fe L-shell absorption. Both XRBs in this study are at a distance of approximately 11 kpc and on the opposite side of the Galactic disk, suggesting that this value could represent the average S depletion of the Milky Way when integrated across all phases of the ISM.

Publications of the Astronomical Society of JapanVol. 77(Supplement_1)
Hiroshima University (JP), Goddard Space Flight Center (US), European Southern Observatory (DE), Rikkyo University (JP), Tokyo City University (JP), Wayne State University (US), University of Michigan (US), University of Teacher Education Fukuoka (JP), Japan Aerospace Exploration Agency (JP), European Space Agency (FR), Center for Astrophysics Harvard & Smithsonian (US), Astronomical Institute of the Slovak Academy of Sciences (SK), Ehime University (JP), European Space Research and Technology Centre (NL), Space Research Organisation Netherlands (NL), Massachusetts Institute of Technology (US), University of Maryland, College Park (US)
National Science Foundation, National Aeronautics and Space Administration, European Space Agency, Ministry of Education, Culture, Sports, Science and Technology, Nuclear Safety and Security Commission, Smithsonian Astrophysical Observatory, Japan Society for the Promotion of Science
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Openalex Percentile: Top 8%
High-pressure geophysics and materials
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