The Feasibility of Using Fe XXIII Metastable Transitions as a Density Diagnostic for Low-mass X-Ray Binary Disk Winds
Year: 2025
Type: article
Abstract: Low-mass X-ray binaries (LMXBs) occasionally show signs of outflowing material from the accretion disk. Studying these outflows can inform the understanding of the geometry of the systems, as well as the dynamics and energetics of accretion. One key variable for determining the location of these disk winds is the density of the outflowing material. In this paper we explore a density diagnostic based upon the absorption of ionizing photons by density-sensitive metastable states of Fe XXIII . This can yield a blueshifted complex of absorption features in the region of 6.61–6.64 keV. We use the photoionization code pion to test how varying the ionizing spectrum affects the detectability and interpretation of these features. We base these ionizing spectral energy distributions on GX 13+1 to represent a bright thermally dominated spectrum, 4U 1735−44 to represent a harder, fainter LMXB spectrum, and MAXI J1820+070 to represent a black hole (BH) LMXB spectrum completely dominated by Comptonized emission. For each of these, we find that the regime where Fe XXIII can be used as a density diagnostic is with an ionization parameter log ( ξ / erg cm s − 1 ) ∼ 2 – 3 and an outflow density log ( n H / cm − 3 ) ≳ 14 . The typical range of ionization parameters for LMXBs indicates that this technique is more feasibly achieved with BH LMXBs than their neutron star counterparts.
Source: The Astrophysical Journal
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $4,499
Awards: G1492468017, G1805294933, G1960117224, G2317628103, G244760476, G3300802746, 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., G629320885, G7149163316, G7652212661, Astronomy at Durham 2020-2023, G866340228
OpenAlex ID: W7116827707