Year: 2025
Type: article
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.
DOI: 10.1093/pasj/psaf068
Authors: Lía Corrales, Elisa Costantini, Sascha Zeegers, Liyi Gu, Hiromitsu Takahashi, David L Moutard, Megumi Shidatsu, Jon M Miller, Misaki Mizumoto, Randall K Smith, Ralf Ballhausen, Priyanka Chakraborty, María Díaz Trigo, Renee M Ludlam, Takao Nakagawa, Ioanna Psaradaki, Shinya Yamada, Caroline A Kilbourne
Institutions: University of Michigan, Space Research Organisation Netherlands, University of Amsterdam, European Space Agency, European Space Research and Technology Centre, Hiroshima University, Ehime University, University of Teacher Education Fukuoka, Center for Astrophysics Harvard & Smithsonian, Goddard Space Flight Center, University of Maryland, College Park, European Southern Observatory, Wayne State University, Tokyo City University, Japan Aerospace Exploration Agency, Institute of Space and Astronautical Science, Massachusetts Institute of Technology, Rikkyo University
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: Yamada Science Foundation, 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
Awards: G1390571956, Investigation of the expression mechanism of the narrow line region in active galactic nuclei, Search for snow-lines with high-resolution spectroscopic observations in the mid-infrared, G1960117224, G201248631, Ultra-light telescope for the detection of snow-lines, G3220404094, G3738269475, G3782671888, G5482575541, G5919148132, THE SIZE DISTRIBUTION AND MINERAL COMPOSITION OF INTERSTELLAR DUST AFFECTS GAS COOLING AND THE EFFICIENCY OF RADIATION PRESSURE DRIVEN WINDS. IDENTIFYING THE DUST GRAIN MINERALS IS ALSO IMPORTANT FOR UNDERSTANDING THE LIFE CYCLE OF DUST -- FROM DESTRUCTION IN THE DIFFUSE INTERSTELLAR MEDIUM (ISM) TO GRAIN GROWTH IN COLD MOLECULAR CLOUDS. USING X-RAY BRIGHT SOURCES ONE CAN MEASURE ABSOLUTE INTERSTELLAR METAL ABUNDANCES FROM PHOTOELECTRIC ABSORPTION AND INVESTIGATE INTERSTELLAR DUST MINERALOGY THROUGH X-RAY ABSORPTION AND SCATTERING. THE SPECTROSCOPIC IMAGING CAPABILITIES OF THE XARM-SXS OFFER UNIQUE OPPORTUNITIES TO STUDY THE SPECTRUM OF DUST SCATTERING HALOS NOT JUST THEIR EFFECT ON PHOTOELECTRIC ABSORPTION. THESE SCATTERING HALOS ARE LARGER THAN OR COMPARABLE TO THE FIELD OF VIEW FOR THE XARMSXS. THE 1.3 ARCMIN HPD EXPECTED FOR XARM WILL ALSO CAUSE POINT SOURCE LIGHT TO MIX WITH DUST SCATTERED LIGHT AND VICE VERSA. AS AN XARM PARTICIPATING SCIENTIST I WILL RUN RAY-TRACE SIMULATIONS OF DUST SCATTERING HALOS TO EVALUATE: (I) THE OBSERVATIONAL APPROACH FOR XARM TO OBTAIN A HIGH RESOLUTION SPECTRUM OF A DUST SCATTERING HALO. THIS WOULD PROVIDE A DIRECT EXPERIMENTAL MEASUREMENT OF THE INTERSTELLAR DUST SCATTERING CROSS-SECTION IN HIGH RESOLUTION WHICH WILL EXHIBIT RESONANT FEATURES AROUND THE K AND L SHELL EDGE ENERGIES THAT WILL DIRECTLY IDENTIFY THE SOLID-PHASE CONSTITUENTS OF THE SCATTERING MATERIAL; AND (II) IDEAL TARGETS AND EXPOSURE TIME NEEDED TO BE ABLE TO RESOLVE X-RAY ABSORPTION FINE STRUCTURE (XAFS) FROM SOLID-PHASE INTERSTELLAR METALS WHICH CAN BE USED TO IDENTIFY THE MINERAL STRUCTURE OF INTERSTELLAR DUST GRAINS. HIGH RESOLUTION MEASUREMENT OF THE DUST SCATTERING CROSS-SECTION: TO MEASURE THE DUST SCATTERING CROSS-SECTION ONE NEEDS TO NORMALIZE THE SCATTERING HALO SPECTRUM BY THE POINT SOURCE SPECTRUM. I AM AN EXPERT ON MODELING THE SURFACE BRIGHTNESS PROFILES OF DUST SCATTERING HALOS. I WILL USE MIE SCATTERING THEORY TO CALCULATE DUST SCATTERING HALOS AROUND THE ABSORPTION EDGE FEATURES EXPECTED FOR TYPICAL DUST MATERIALS. I WILL SIMULATE THE SCATTERING HALOS UNDER THE EFFECTS OF BACKGROUND SOURCE SPECTRA WITH VARYING DEGREES OF SPECTRAL SMOOTHNESS (E.G. A FEATURELESS POWER LAW VERSUS A SPECTRUM WITH AN EMISSION LINE OVERLAPPING THE ABSORPTION EDGE POSITION). I WILL RUN MY SIMULATIONS THROUGH RAY-TRACING SOFTWARE IN ORDER TO EVALUATE THE EFFECTS OF THE XARM PSF MIXING WITH THE DUST SCATTERING HALO. THE RESULTS WILL DETERMINE WHETHER MEASUREMENTS OF THE DUST SCATTERING CROSS-SECTION CAN BE DONE WITH XARM ALONE OR IF COORDINATED OBSERVATIONS WITH CHANDRA OR XMM-NEWTON ARE NEEDED. XAFS WITH XARM: MY WORK HAS SHOWN THAT DUST SCATTERING HALOS CAN ALTER THE APPARENT SHAPE AND DEPTH OF THE PHOTOELECTRIC ABSORPTION EDGE -- DEPENDING ON GRAIN SIZES LOCATION AND IMAGING RESOLUTION OF THE X-RAY TELESCOPE OF INTEREST. I WILL USE THE RAY-TRACING SIMULATIONS DESCRIBED ABOVE TO EVALUATE HOW THE DUST SCATTERING HALO WILL AFFECT XARM SPECTRA. I WILL DETERMINE IDEAL TARGETS EXPOSURE TIME AND SIGNAL-TO-NOISE NECESSARY TO CHOOSE BETWEEN XAFS TEMPLATES FOR DIFFERENT MINERALS. MY MAIN SCIENCE FOCUS WILL BE ON THE FOLLOWING QUESTIONS: - WHERE IS THE X-RAY SIGNATURE OF SOLID O? RECENT WORK UTILIZING THE MOST UP-TO-DATE THEORETICAL O CROSS-SECTIONS SHOW THAT THE O K EDGE CAN BE DESCRIBED BY GAS-ONLY MODELS. YET OXYGEN IS A CRUCIAL INGREDIENT FOR SILICATE MINERALS. IDENTIFYING A 0.5 KEV FEATURE IN THE DUST SCATTERING CROSS-SECTION WILL UNAMBIGUOUSLY RESOLVE THIS ISSUE. - IS THERE ANY GAS PHASE NEUTRAL FE AND IF SO WHAT IS THE ABSORPTION CROSS SECTION? WE CAN SEARCH FOR RESIDUALS IN THE FE L SHELL EDGE TO DIRECTLY MEASURE THE CROSS-SECTION OF NEUTRAL FE. - CAN WE EXAMINE PAHS WITH X-RAYS? DUE TO INCREASED ABSORPTION C K EDGE FEATURES HAVE BEEN IDENTIFIED IN ONLY A FEW SOURCES WITH LOW ISM COLUMN. I WILL EVALUATE THE ABILITY OF XARM TO RESOLVE FEATURES FROM C K (0.3 KEV) NEAR THE LIMIT OF THE SXS BANDPASS., Collaborative Research: Dust Echo Tomography: New Diagnostics for Galactic Dust and Magnetic Fields, G866340228
OpenAlex ID: W4411765254