arXiv subjects

Hiroya Yamaguchi

Publications and source records attributed to Hiroya Yamaguchi.

At least 19 recordsLinked to original sources

arXiv2026

Progenitor and Explosion Mechanism of 3C 397 Indicated from XRISM High-resolution Spectroscopy of Fe-group Elements

We present spatially resolved X-ray spectroscopy of the Type Ia supernova remnant 3C 397, one of the most promising candidates to have originated from a white dwarf with a mass close to the Chandrasekhar limit. The remnant was observed during the performance verification phase of the X-ray Imaging and Spectroscopy Mission (XRISM), with the field of view of the Resolve calorimeter array positioned on the eastern half of the remnant. We divide the Resolve field of view into southeastern and northeastern regions and extract spectra from each region for both Resolve and Xtend. The Resolve spectra are characterized by narrow K-shell emission lines from intermediate-mass elements (IMEs) such as Si, S, Ar, and Ca, and by broader K-shell emission lines from iron-group elements (IGEs) such as Cr, Mn, Fe, and Ni. K-shell emission lines from Ti and Cr are also detected, and are found to be locally enhanced in the southeastern region, as reported in previous observations. We model the Resolve and Xtend spectra simultaneously by a non-equilibrium ionization (NEI) plasma model with multiple temperatures and ionization states. The observed mass ratios of Ti/Fe and Cr/Fe in the southeastern region can only be explained by nucleosynthesis in a neutron-rich environment produced by electron-capture reactions in the innermost layers of the exploding white dwarf. By comparing the observed mass ratios with those predicted by nucleosynthesis models, we constrain the central density to be >= 4.0 x 10^9 g cm^{-3} for the deflagration-to-detonation transition model and >= 6.0 x 10^9 g cm^{-3} for the pure turbulent deflagration model. On the other hand, the observed Ni/Fe mass ratio is globally enhanced across the field of view, suggesting an additional neutronization mechanism beyond electron-capture reactions, such as a higher progenitor metallicity.

astro-ph.HE↗

arXiv2026

Distinct Velocity Components in the Absorption Lines of the Neutron Star X-ray Binary AX J1745.6-2901

Accretion disks in X-ray binaries regulate mass transfer onto compact objects and drive radiative and kinetic feedback to their surroundings. Here we report X-ray spectroscopy of the eclipsing neutron star low-mass X-ray binary AX J1745.6-2901 with XRISM/Resolve. The phase-averaged Fe XXVI Ly{\alpha} absorption profile exhibits two absorption minima with relative depths that are inconsistent with the theoretical Ly{\alpha}1/Ly{\alpha}2 doublet ratio expected from a single velocity component. We demonstrate that this profile is well described by two discrete velocity components: a blueshifted component at v~ -160 km/s and a redshifted component at v ~ +590 km/s. The significance of the redshifted component is more than 3 sigma based on a Monte-Carlo calculation. This velocity structure persists across orbital phases, disfavoring a localized origin such as a bulge or dip. The blueshifted component, well below the outer-disk escape velocity, is consistent with a slow outflow or disk atmosphere. The redshifted absorber can be explained either by infalling gas from a failed wind or by a gravitational redshift, and the present data cannot rule out either possibility. Regardless of its origin, the redshifted component is kinematically separate from the disk atmosphere and outflow. The absence of absorption at intermediate velocities further indicates a genuinely bimodal velocity distribution rather than the two ends of a single continuous flow, offering a new view of the absorbing-gas kinematics.

astro-ph.HE↗

arXiv2026

Kinetic structure of the intracluster medium across nearby clusters observed with XRISM

XRISM/Resolve is building a sample of galaxy clusters with directly measured ICM gas motions, revealing diverse projected dynamical states. We compile 45 XRISM/Resolve measurements in 19 nearby galaxy clusters and place them on a common, emission-weighted effective line-of-sight scale, $\ell_{\rm eff}$. We compare the line-of-sight velocity dispersion $\sigma_v$, bulk velocity amplitude $|v_{\rm bulk}|$, their ratio $R_v \equiv |v_{\rm bulk}|/\sigma_v$, and non-thermal pressure proxies. Disturbed non-cool-core systems are not simply higher-dispersion counterparts of relaxed cool-core regions. Instead, differences among cool-core centers, cool-core outer regions, and non-cool-core systems are driven mainly by coherent line-of-sight motion relative to unresolved line broadening: $R_v$ tends to remain below unity in cool-core regions but often exceeds unity in non-cool-core systems, with the mean $R_v$ rising from 0.45 in cool-core centers to 1.6 in non-cool-core systems. These diagnostics help separate local central line broadening, likely associated with AGN feedback in some cool cores, from larger-scale coherent motions associated with sloshing, mergers, and halo assembly. Comparison with forward-modeled TNG-Cluster predictions suggests that many cool-core measurements occupy the lower part of the predicted non-thermal pressure range, consistent with small hydrostatic-mass corrections in relaxed systems and larger corrections in disturbed ones. XRISM is thus beginning to resolve the projected kinetic structure of the ICM across cluster environments, rather than tracing a single sequence of increasing turbulence.

astro-ph.CO↗

arXiv2026

The line modulations of H-like Fe, Ca, Ar, and S observed with $XRISM$/Resolve in Cyg X-3

Cygnus X-3, hosting a Wolf-Rayet (WR) star whose dense wind produces various spectral lines due to photoionization by X-rays from a compact object, provides an ideal laboratory for studying wind dynamics and density structure. We measured the orbital modulations of the Fe, Ca, Ar, and S Ly$\alpha$ lines observed with the X-ray microcalorimeter (Resolve) onboard the $XRISM$, taking account of both emission and absorption lines of the Ly$\alpha$ complexes. The modulations of Doppler shifts of the Fe, Ca, Ar, and S Ly$\alpha$ lines showed amplitudes of 500 km s$^{-1}$ and phase offsets of 0.04, 0.09, 0.11, and 0.17, respectively, in units of an orbital period (4.8 hours) relative to the orbital motion of the compact object. This result indicated that H-like Fe most closely follows the compact object's motion. The line widths ranged from 400 to 1000 km s$^{-1}$. The intensities of both emission and absorption lines reached their minima around orbital phase 0.0 and their maxima around phase 0.5. The absorption peaks, however, did not align exactly with phase 0.5, suggesting the inhomogeneous structures such as an accretion wake and/or a bow shock. We compared the observed modulations with calculations based on a stellar wind model, accelerated by ultraviolet radiation from the WR star. One of the calculations qualitatively reproduced the observed trend that H-like Fe ions were concentrated near the compact object, whereas H-like S was distributed across the binary system, with H-like Ca and Ar showing intermediate spatial distributions. From this comparison, we estimated that a mass-loss rate of the stellar wind was approximately $5 \times 10^{-6}$-$1 \times 10^{-5}\ M_{\odot}\ {\rm yr}^{-1}$.

astro-ph.HE↗

arXiv2026

Spectral and photometric variability of SS 433 observed with XRISM and simultaneous optical and near-infrared telescopes

We present results from coordinated multiwavelength observations of the SS 433, obtained with XRISM, optical telescopes, and near-infrared camera during 2024 April and 2025 March. The XRISM exposures amounted to ~200 ks in 2024 and ~100 ks in 2025. With XRISM/Resolve's high spectral resolution and large effective area, we clearly resolved numerous emission lines even in short time segments, achieving improved accuracy in Doppler-shift measurements relative to earlier observations. The simultaneously obtained X-ray and optical Doppler shifts suggest a possible tendency for the optical emission to lag slightly behind the X-rays. In the Resolve data, the Doppler shifts of the two jet components exhibited apparent asymmetries, with jet speeds fluctuating around ~0.26$\pm$0.01$c$ in 2024 and ~0.30$\pm$0.01$c$ in 2025. The velocity variations indicated modulations on a timescale of ~6.3 d, with a phase offset of about -90$^{\circ}$ relative to the nutation cycle. The observed line widths and flux of the approaching and receding jets appear consistent with the expected geometrical effects, indicating systematically larger line widths in the inner regions of the jets, as proposed by Shidatsu et al. (2025). Optical light curves show flares of ~400 s in 2024 and ~1600 s in 2025, with amplitudes up to ~15% during out-of-eclipse intervals, while the XRISM/Xtend light curves show no significant variability within the overlapping intervals and given the statistical uncertainties. Near-infrared photometry in 2024, obtained during an out-of-eclipse interval at a different epoch from the optical observations, showed no flare-like variability, and the X-ray band also remained constant within uncertainties. These coordinated observations provide a foundation for future XRISM studies aimed at probing the dynamical properties of the relativistic jets in SS 433.

astro-ph.HE↗

arXiv2026

Photoexcitation spectroscopy of highly charged ions for application to astronomy using a compact electron beam ion trap (EBIT) at the synchrotron radiation facility SPring-8

In the past few decades, X-ray astronomy satellites equipped with grating spectrometers and microcalorimeters have enabled high-resolution spectroscopic observations of astrophysical objects. The need for accurate atomic data has arose as we attempt detailed analysis of the high-resolution spectra they provide. This is because current spectral models, which heavily rely on theoretical calculations, entail non-negligible uncertainties. We employ a plasma spectroscopy device called electron beam ion trap (EBIT) to experimentally obtain precise atomic data. An EBIT with a design that allows combined operation with synchrotron radiation facilities was developed based on the Heidelberg Compact EBIT and installed at ISAS/JAXA for this purpose. We conducted a spectroscopic experiment using the JAXA-EBIT at the synchrotron radiation facility SPring-8, and successfully obtained high-resolution spectra of the L$\alpha$ resonance transition of Ne-like Fe$^{16+}$ ions, 3C, as well as the K$\alpha$ resonance transition of He-like O$^{6+}$ ions. We also measured another Ne-like Fe$^{16+}$ L$\alpha$ resonance transition, 3G, and constrained an upper limit of the oscillator strength ratio of 3G to 3C, using our experimental results. The experimental values obtained in this study will be applied to observational studies of astrophysical objects as a part of the plasma spectral modeling.

astro-ph.IM↗

arXiv2026

Energy shift of Fe-K fluorescence lines due to low ionization demonstrated with XRISM in Centaurus X-3

The Fe K$\alpha$ fluorescence line at 6.4 keV is a powerful probe of cold matter surrounding X-ray sources and has been widely used in various astrophysical contexts. The X-ray microcalorimeter spectrometer onboard XRISM can measure line shifts with unprecedented precision of $\sim$0.2 eV, equivalent to a line-of-sight velocity of $\sim$10 km s$^{-1}$. At this level of accuracy, however, several factors that influence the line energy must be carefully considered prior to astrophysical interpretation. One such important factor is the ionization degree, Fe$^{q+}$. The K$\alpha$ line shifts redward by $\sim$4 eV as $q$ increases from 0 (neutral) to 8 (Ar-like). Additionally, the accompanying Fe K$\beta$ line at 7.06 keV shifts blueward by $\sim$30 eV from $q=0$ to 8. We demonstrate that this effect is actually observable in the XRISM data of the high-mass X-ray binary Centaurus X-3 (Cen X-3). We advocate that the differential energy shift between the K$\alpha$ and K$\beta$ line provides a robust estimate of $q$ by decoupling from other effects that shift the two lines in the same direction. We derived $q \sim 5$ (Sc-like) for the fluorescing matter by comparing the observation with atomic structure calculations of our own and in the literature. By accounting for the derived charge state and the corresponding shift in the rest-frame line energy, we made corrections for this effect and reached a consistent residual shift among the K$\alpha$, K$\beta$, and the optical measurement attributable to the systemic velocity of the system. Consequently, we obtained a new constraint on the location of the cold matter. This ionization effect needs to be assessed in all use cases of the Fe K$\alpha$ line shift beyond Cen X-3, and the proposed metric is generally applicable to all of them.

astro-ph.HE↗

arXiv2026

Asymmetric distribution of Fe-peak elements in Cassiopeia A revealed by XRISM

The elemental abundances of the Fe-peak elements (such as Cr, Mn, Fe and Ni) and Ti are important for understanding the environment of explosive nuclear burning for the core-collapse supernovae (CC SNe). In particular, the supernova remnant Cassiopeia A, which is well known for its asymmetric structure, contains three ``Fe-rich blobs,'' and the composition of the Fe-peak elements within these structures could be related to the asymmetry of the supernova explosion. We report a highly asymmetric distribution of the Fe-peak elements in Cassiopeia A as revealed by XRISM observations. We found that the southeastern Fe-rich region has a significant Mn emission above the 4$\sigma$ confidence level, while the northwestern Fe-rich region has no clear signature. In addition to the significant difference in Mn abundance across these regions, our observations show that the Ti/Fe, Mn/Cr, and Ni/Fe ratios vary from region to region. The observed asymmetric distribution of Fe-peak elements could be produced by (1) the mixing of materials from different burning layers of the supernova, (2) the asymmetric distribution of the electron fraction in the progenitor star and/or (3) the local dependence of the neutrino irradiation in the supernova innermost region. Future spatially resolved spectroscopy of Cassiopeia A using X-ray microcalorimeters will enable more detailed measurements of the distribution and composition of these elements, providing a unique tool for testing asymmetric supernova physics.

astro-ph.HE↗

arXiv2025

A laboratory plasma experiment for X-ray astronomy using a compact electron beam ion trap (EBIT)

We present the basic performance and experimental results of an electron beam ion trap (JAXA-EBIT), newly introduced to the Japanese astronomical community. Accurate atomic data are indispensable for the reliable interpretation of high-resolution X-ray spectra of astrophysical plasmas. The JAXA-EBIT generates highly charged ions under well-controlled laboratory conditions, providing experimental benchmarks for atomic data. The JAXA-EBIT shows performance comparable to the Heidelberg compact EBIT through dielectronic recombination measurements of highly charged Ar ions. Furthermore, we conducted resonant photoexcitation spectroscopy of highly charged ions using the soft X-ray beamline BL17SU at the synchrotron radiation facility SPring-8. As a result, we successfully detected resonance transitions of He-like O$^{6+}$ and Ne-like Fe$^{16+}$. These results demonstrate the capability of the JAXA-EBIT for precise measurement of atomic data and show that it serves as a powerful tool for advancing astrophysical research.

astro-ph.IM↗

arXiv2025

Spatially Resolved Plasma Diagnostics of the Supernova Remnant DEM L71 using the Reflection Grating Spectrometer

We present a spatially resolved high-resolution X-ray spectroscopy of the supernova remnant DEM L71 using the Reflection Grating Spectrometer (RGS) aboard XMM-Newton. Because of the large dispersion angle of the RGS, we are able to resolve individual emission lines and examine their spatial distributions within this moderately extended remnant. We derive line fluxes across different regions of DEM L71 and perform quantitative plasma diagnostics. Our analysis reveals that some regions have high forbidden-to-resonance ratios of O\emissiontype{VII} He$\alpha$ lines, suggesting a non-negligible contribution from additional physical processes, such as charge exchange and/or resonance scattering. Our results demonstrate that the RGS has potential to serve as an outstanding X-ray imaging spectrometer for moderately diffuse objects.

astro-ph.HE↗

arXiv2025

Fe XVIII-XXIV K beta Inner-shell Absorption Lines in the X-ray Spectra of Neutron Star and Black Hole Binaries with XRISM

The advent of the X-ray microcalorimeter spectrometer Resolve onboard the XRISM space telescope opened a new era for high-resolution X-ray spectroscopy of astrophysical plasmas. Many spectral features were newly detected, including the K alpha and K beta inner-shell transition lines of mildly ionized (F- to Li-like) Fe at 6-8 keV in the spectra of X-ray binaries and active galactic nuclei. The widely used atomic databases contain information on the K alpha but not K beta lines of these ions. We conducted the atomic structure calculation using FAC to derive the Fe K alpha and K beta lines and verified the result against ground experiments and other calculations of the Fe K alpha lines. We then implemented the Fe K beta lines in a radiative transfer code (cloudy) and compared the synthesized and observed spectra with XRISM. A reasonably good agreement was obtained between the observation and the ab initio calculations. This exemplifies the need to expand the atomic databases to interpret astrophysical spectra.

astro-ph.HE↗

arXiv2025

Chandra Large Project Observations of the Supernova Remnant N132D: Measuring the Expansion of the Forward Shock

We present results from the Chandra X-ray Observatory Large Project (878 ks in 28 observations) of the Large Magellanic Cloud supernova remnant N132D. We measure the expansion of the forward shock in the bright southern rim to be $0.\!^{\prime\prime}10 \pm 0.\!^{\prime\prime}02$ over the $\sim14.5$ yr baseline, which corresponds to a velocity of $1620\pm400~\mathrm{km\,s^{-1}}$ after accounting for several instrumental effects. We measure an expansion of $0.\!^{\prime\prime}23 \pm 0.\!^{\prime\prime}02$ and a shock velocity of $3840\pm260~\mathrm{km\,s^{-1}}$ for two features in an apparent blowout region in the northeast. The emission-measure-weighted average temperature inferred from X-ray spectral fits to regions in the southern rim is $0.95\pm0.17$ keV, consistent with the electron temperature implied by the shock velocity after accounting for Coulomb equilibration and adiabatic expansion. In contrast, the emission-measure-weighted average temperature for the northeast region is $0.77\pm0.04$ keV, which is significantly lower than the value inferred from the shock velocity. We fit 1-D evolutionary models for the shock in the southern rim and northeast region, using the measured radius and propagation velocity into a constant density and power-law profile circumstellar medium. We find good agreement with the age of $\sim2500$ years derived from optical expansion measurements for explosion energies of $1.5-3.0 \times 10^{51}\,\mathrm{erg}$, ejecta masses of $2-6 \,\mathrm{M_{\odot}}$ and ambient medium densities of $\sim0.33-0.66$ $\mathrm{amu~cm}^{-3}$ in the south and $\sim0.01-0.02$ $\mathrm{amu~cm}^{-3}$ in the northeast assuming a constant density medium. These results are consistent with previous studies that suggested the progenitor of N132D was an energetic supernova that exploded into a pre-existing cavity.

astro-ph.HE↗

arXiv2025

XRISM Observations of Cassiopeia A: Overview, Atomic Data, and Spectral Models

Cassiopeia A (Cas A) is the youngest known core-collapse supernova remnant (SNR) in the Galaxy and is perhaps the best-studied SNR in X-rays. Cas A has a line-rich spectrum dominated by thermal emission and given its high flux, it is an appealing target for high-resolution X-ray spectroscopy. Cas A was observed at two different locations during the Performance Verification phase of the XRISM mission, one location in the southeastern part (SE) of the remnant and one in the northwestern part (NW). This paper serves as an overview of these observations and discusses some of the issues relevant for the analysis of the data. We present maps of the so-called ``spatial-spectral mixing'' effect due to the fact that the XRISM point-spread function is larger than a pixel in the Resolve calorimeter array. We analyze spectra from two bright, on-axis regions such that the effects of spatial-spectral mixing are minimized. We find that it is critical to include redshifts/blueshifts and broadening of the emission lines in the two thermal components to achieve a reasonable fit given the high spectral resolution of the Resolve calorimeter. We fit the spectra with two versions of the AtomDB atomic database (3.0.9 and 3.1.0) and two versions of the SPEX (3.08.00 and 3.08.01*) spectral fitting software. Overall we find good agreement between AtomDB 3.1.0 and SPEX 3.08.01* for the spectral models considered in this paper. The most significant difference we found between AtomDB 3.0.9 and 3.1.0 and between AtomDB 3.1.0 and SPEX 3.08.01* is the Ni abundance, with the new atomic data favoring a considerably lower (up to a factor of 3) Ni abundance. Both regions exhibit significantly enhanced abundances compared to Solar values indicating that supernova ejecta dominate the emission in these regions. We find that the abundance ratios of Ti/Fe, Mn/Fe, \& Ni/Fe are significantly lower in the NW than the SE.

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arXiv2025

XRISM spectroscopy on orbital modulation of Fe Ly$\alpha$ lines in Cygnus X-3

To understand physical processes such as mass transfer and binary evolution in X-ray binaries, the orbital parameters of the system are fundamental and crucial information. Cygnus X-3 is a high-mass X-ray binary composed of a compact object of unknown nature and a Wolf-Rayet star, which is of great interest in the context of wind-fed mass accretion and binary evolution. Here we present XRISM/Resolve high-resolution spectroscopy focusing on the Fe Ly$\alpha$ lines in its hypersoft state. We perform an orbital phase-resolved spectral analysis of the lines to study the orbital modulation of the emission and absorption lines. It is found that the emission lines reflect the orbital motion of the compact object whose estimated velocity amplitude is $430^{~~+150}_{~~-140}~~\mathrm{km\,s^{~-1}}$, while the absorption lines show a variation that can be interpreted as originating from the stellar wind. We discuss possible mass ranges for the binary components using the mass function with the estimated value of the velocity amplitude in this work, combined with the relation between the mass loss rate and the orbital period derivative and the empirical mass and mass loss rate relation for Galactic Wolf-Rayet stars. They are constrained to be $(1.3\text{-}5.1)\,M_\odot$ and $(9.3\text{-}12)\,M_\odot$ for the assumed inclination angle of $i = 25$ deg, which becomes more relaxed to $(1.3\text{-}24)\,M_\odot$ and $(9.3\text{-}16)\,M_\odot$ for $i = 35$ deg, respectively. Thus, it remains unclear whether the system harbors a black hole or a neutron star.

astro-ph.HE↗

arXiv2025

Evidence for Charge Exchange Emission in Supernova Remnant N132D from XRISM/Resolve Observations

XRISM has delivered one of its first light observations on N132D, the X-ray brightest supernova remnant in the Large Magellanic Cloud. Utilizing 193 ks of high-resolution X-ray spectroscopy data, we conduct a comprehensive search for charge exchange emission. By incorporating a charge exchange model into our spectral analysis, we observe an improvement in the fits of two weak features at 2.41 keV and 2.63 keV. These features, with a combined significance of 99.6%, are consistent with transitions from highly ionized silicon ions in high Rydberg states, which are unique indicators of charge exchange. Our analysis constrains the charge exchange flux to no more than 4% of the total source flux within the 1.7-3.0 keV band, and places an upper limit on the charge exchange interaction velocity at 450 km/s. This result supports ongoing shock-cloud interactions within N132D and highlights the unique capabilities of XRISM to probe the complex physical processes at play.

astro-ph.HE↗

arXiv2025

Dynamics of the intermediate-mass-element ejecta in the Supernova Remnant Cassiopeia A studied with XRISM

Supernova remnants (SNRs) provide crucial information of yet poorly understood mechanism of supernova explosion. Here we present XRISM high-resolution spectroscopy of the intermediate-mass-element (IME) ejecta in the SNR Cas A to determine their velocity distribution and thermal properties. The XRISM/Resolve spectrum in the 1.75-2.95 keV band extracted from each $1' \times 1'$ region in the southeast and northwest rims is fitted with a model consisting of two-component plasmas in non-equilibrium ionization with different radial velocities and ionization timescales. It is found that the more highly ionized component has a larger radial velocity, suggesting that this component is distributed in the outer layer and thus has been heated by the SNR reverse shock earlier. We also perform proper motion measurement of the highly ionized component (represented by the Si XIV Ly$\alpha$ emission), using archival Chandra data, to reconstruct the three-dimensional velocity of the outermost IME ejecta. The pre-shock (free expansion) velocity of these ejecta is estimated to range from 2400 to 7100 km s$^{-1}$, based on the thermal properties and the bulk velocity of the shocked ejecta. These velocities are consistent with theoretical predictions for a Type IIb supernova, in which the progenitor's hydrogen envelope is largely stripped before the explosion. Furthermore, we find a substantial asymmetry in the distribution of the free expansion velocities, with the highest value toward the direction opposite to the proper motion of the neutron star (NS). This indicates the physical association between the asymmetric supernova explosion and NS kick.

astro-ph.HE↗

arXiv2025

Measurement of the Forward Shock Velocities of the Supernova Remnant N132D Based on the Thermal X-ray Emission

Measuring shock velocities is crucial for understanding the energy transfer processes at the shock fronts of supernova remnants (SNRs), including acceleration of cosmic rays. Here we present shock velocity measurements on the SNR N132D, based on the thermal properties of the shock-heated interstellar medium. We apply a self-consistent model developed in our previous work to X-ray data from deep Chandra observations with an effective exposure of $\sim$ 900 ks. In our model, both temperature and ionization relaxation processes in post-shock plasmas are simultaneously calculated, so that we can trace back to the initial condition of the shock-heated plasma to constrain the shock velocity. We reveal that the shock velocity ranges from 800 to 1500 $\rm{km~s^{-1}}$ with moderate azimuthal dependence. Although our measurement is consistent with the velocity determined by independent proper motion measurements in the south rim regions, a large discrepancy between the two measurements (up to a factor of 4) is found in the north rim regions. This implies that a substantial amount of the kinetic energy has been transferred to the nonthermal component through highly efficient particle acceleration. Our results are qualitatively consistent with the $\gamma$-ray observations of this SNR.

astro-ph.HE↗

arXiv2024

A self-consistent model of shock-heated plasma in non-equilibrium states for direct parameter constraints from X-ray observations

X-ray observations of shock-heated plasmas, such as those found in supernova remnants, often exhibit features of temperature and ionization non-equilibrium. For accurate interpretation of these observations, proper calculations of the equilibration processes are essential. Here, we present a self-consistent model of thermal X-ray emission from shock-heated plasmas that accounts for both temperature and ionization non-equilibrium conditions. For a given pair of shock velocity and initial electron-to-ion temperature ratio, the temporal evolution of the temperature and ionization state of each element was calculated by simultaneously solving the relaxation processes of temperature and ionization. The resulting thermal X-ray spectrum was synthesized by combining our model with the AtomDB spectral code. Comparison between our model and the \texttt{nei} model, a constant-temperature non-equilibrium ionization model available in the XSPEC software package, reveals a 30\% underestimation of the ionization timescale in the \texttt{nei} model. We implemented our model in XSPEC to directly constrain the shock wave properties, such as the shock velocity and collisionless electron heating efficiency, from the thermal X-ray emission from postshock plasmas. We applied this model to archival Chandra data of the supernova remnant N132D, providing a constraint on the shock velocity of $\sim 800~\mathrm{km\,s^{-1}}$, in agreement with previous optical studies.

astro-ph.HE↗