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Shoji Ogawa

Publications and source records attributed to Shoji Ogawa.

At least 37 records · Page 2Linked to original sources

XRISM constraints on unidentified X-ray emission lines, including the 3.5 keV line, in the stacked spectrum of ten galaxy clusters

We stack 3.75 Megaseconds of early XRISM Resolve observations of ten galaxy clusters to search for unidentified spectral lines in the $E=$ 2.5-15 keV band (rest frame), including the $E=3.5$ keV line reported in earlier, low spectral resolution studies of cluster samples. Such an emission line may originate from the decay of the sterile neutrino, a warm dark matter (DM) candidate. No unidentified lines are detected in our stacked cluster spectrum, with the $3σ$ upper limit on the $m_{\rm s}\sim$ 7.1 keV DM particle decay rate (which corresponds to a $E=3.55$ keV emission line) of $Γ\sim 1.0 \times 10^{-27}$ s$^{-1}$. This upper limit is 3-4 times lower than the one derived by Hitomi Collaboration et al. (2017) from the Perseus observation, but still 5 times higher than the XMM-Newton detection reported by Bulbul et al. (2014) in the stacked cluster sample. XRISM Resolve, with its high spectral resolution but a small field of view, may reach the sensitivity needed to test the XMM-Newton cluster sample detection by combining several years worth of future cluster observations.

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Emission and Absorption Features of Magnetically Driven Disk Winds in Black Hole X-Ray Binaries

We investigate accretion disk winds commonly observed in galactic black hole (BH) X-ray binaries (XRB), which manifest as blueshifted absorption features in X-ray spectra. We model these winds as ideal magnetohydrodynamic outflows of hot plasma driven by global magnetic fields threading the accretion disk around the BH. Using Monte Carlo simulations with MONACO, we solve three-dimensional radiative transfer equations to determine the large-scale ionization structure that produces the observed ionic column densities. Focusing on the high/soft state of the BH XRB, where disk emission provides the dominant source of ionizing X-rays, we calculated synthetic spectra showing resonance absorption and scattered emission from ions in various charge states. Our results demonstrate that systems viewed at high polar angles exhibit prominent multi-ion absorption lines with asymmetric profiles, accompanied by P-Cygni-like emission features that partially reproduce the characteristics seen in the observed spectra. This further implies that even a dense disk wind with a high polar angle is unlikely to be saturated due to effective scattering.

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Probing Accretion Disk Winds of Stratified Nature with Fe XXVI Doublet in Black Hole X-ray Binaries

Powerful ionized accretion disk winds are often observed during episodic outbursts in Galactic black hole transients. Among those X-ray absorbers, \fexxvi\ doublet structure (Ly$α_1$+Ly$α_2$ with $\sim 20$eV apart) has a unique potential to better probe the underlying physical nature of the wind; i.e. density and kinematics. We demonstrate, based on a physically-motivated magnetic disk wind scenario of a stratified structure in density and velocity, that the doublet line profile can be effectively utilized as a diagnostics to measure wind density and associated velocity dispersion (due to thermal turbulence and/or dynamical shear motion in winds). Our simulated doublet spectra with post-process radiative transfer calculations indicate that the profile can be (1) broad with a single peak for higher velocity dispersion ($\gsim 5,000$ km~s$^{-1}$), (2) a standard shape with 1:2 canonical flux ratio for moderate dispersion ($\sim 1,000-5,000$ km~s$^{-1}$) or (3) double-peaked with its flux ratio approaching 1:1 for lower velocity dispersion ($\lsim 1,000$ km~s$^{-1}$) in optically-thin regime, allowing various line shape. Such a diversity in doublet profile is indeed unambiguously seen in recent observations with XRISM/Resolve at microcalorimeter resolution. We show that some implications inferred from the model will help constrain the local wind physics where \fexxvi\ is predominantly produced in a large-scale, stratified wind.

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Discovery of Powerful Multi-Velocity Ultra-Fast Outflows in the Starburst Merger Galaxy IRAS 05189$-$2524 with XRISM

We observed the X-ray-bright ultra-luminous infrared galaxy, IRAS 05189$-$2524, with XRISM during its performance verification phase. The unprecedented energy resolution of the onboard X-ray microcalorimeter revealed complex spectral features at $\sim$7$-$9 keV, which can be interpreted as blueshifted Fe XXV/XXVI absorption lines with various velocity dispersions, originating from ultra-fast outflow (UFO) components with multiple bulk velocities of $\sim0.076c$, $\sim0.101c$, and $\sim0.143c$. In addition, a broad Fe-K emission line was detected around $\sim7$ keV, forming a P Cygni profile together with the absorption lines. The onboard X-ray CCD camera revealed a 0.4$-$12 keV broadband spectrum characterized by a neutrally absorbed power-law continuum with a photon index of $\sim2.3$, and intrinsic flare-like variability on timescales of $\sim10$ ksec, both of which are likely associated with near-Eddington accretion. We also found potential variability of the UFO parameters on a timescale of $\sim140$ ksec. Using these properties, we propose new constraints on the outflow structure and suggest the presence of multiple outflowing regions on scales of about tens to a hundred Schwarzschild radii, located within roughly two thousand Schwarzschild radii. Since both the estimated momentum and energy outflow rates of the UFOs exceed those of galactic molecular outflows, our results indicate that powerful, multi-velocity UFOs are already well developed during a short-lived evolutionary phase following a major galaxy merger, characterized by intense starburst activity and likely preceding the quasar phase. This system is expected to evolve into a quasar, sustaining strong UFO activity and suppressing star formation in the host galaxy.

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Comparing XRISM cluster velocity dispersions with predictions from cosmological simulations: are feedback models too ejective?

The dynamics of the intra-cluster medium (ICM), the hot plasma that fills galaxy clusters, are shaped by gravity-driven cluster mergers and feedback from supermassive black holes (SMBH) in the cluster cores. XRISM measurements of ICM velocities in several clusters offer insights into these processes. We compare XRISM measurements for nine galaxy clusters (Virgo, Perseus, Centaurus, Hydra A, PKS\,0745--19, A2029, Coma, A2319, Ophiuchus) with predictions from three state-of-the-art cosmological simulation suites, TNG-Cluster, The Three Hundred Project GADGET-X, and GIZMO-SIMBA, that employ different models of feedback. In cool cores, XRISM reveals systematically lower velocity dispersions than the simulations predict, with all ten measurements below the median simulated values by a factor $1.5-1.7$ on average and all falling within the bottom $10\%$ of the predicted distributions. The observed kinetic-to-total pressure ratio is also lower, with a median value of $2.2\%$, compared to the predicted $5.0-6.5\%$ for the three simulations. Outside the cool cores and in non-cool-core clusters, simulations show better agreement with XRISM measurements, except for the outskirts of the relaxed, cool-core cluster A2029, which exhibits an exceptionally low kinetic pressure support ($<1\%$), with none of the simulated systems in either of the three suites reaching such low levels. The non-cool-core Coma and A2319 exhibit dispersions at the lower end but within the simulated spread. Our comparison suggests that the three numerical models may overestimate the kinetic effects of SMBH feedback in cluster cores. Additional XRISM observations of non-cool-core clusters will clarify if there is a systematic tension in the gravity-dominated regime as well.

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Stratified wind from a super-Eddington X-ray binary is slower than expected

Accretion discs in strong gravity ubiquitously produce winds, seen as blueshifted absorption lines in the X-ray band of both stellar mass X-ray binaries (black holes and neutron stars), and supermassive black holes. Some of the most powerful winds (termed Eddington winds) are expected to arise from systems where radiation pressure is sufficient to unbind material from the inner disc ($L\gtrsim L_{\rm Edd}$). These winds should be extremely fast and carry a large amount of kinetic power, which, when associated with supermassive black holes, would make them a prime contender for the feedback mechanism linking the growth of those black holes with their host galaxies. Here we show the XRISM Resolve spectrum of the Galactic neutron star X-ray binary, GX 13+1, which reveals one of the densest winds ever seen in absorption lines. This Compton-thick wind significantly attenuates the flux, making it appear faint, although it is intrinsically more luminous than usual ($L\gtrsim L_{\rm Edd}$). However, the wind is extremely slow, more consistent with the predictions of thermal-radiative winds launched by X-ray irradiation of the outer disc, than with the expected Eddington wind driven by radiation pressure from the inner disc. This puts new constraints on the origin of winds from bright accretion flows in binaries, but also highlights the very different origin required for the ultrafast ($v\sim 0.3c$) winds seen in recent Resolve observations of a supermassive black hole at similarly high Eddington ratio.

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XRISM/Resolve View of Abell 2319: Turbulence, Sloshing, and ICM Dynamics

We present results from XRISM/Resolve observations of the core of the galaxy cluster Abell 2319, focusing on its kinematic properties. The intracluster medium (ICM) exhibits temperatures of approximately 8 keV across the core, with a prominent cold front and a high-temperature region ($\sim$11 keV) in the northwest. The average gas velocity in the 3 arcmin $\times$ 4 arcmin region around the brightest cluster galaxy (BCG) covered by two Resolve pointings is consistent with that of the BCG to within 40 km s$^{-1}$ and we found modest average velocity dispersion of 230-250 km s$^{-1}$. On the other hand, spatially-resolved spectroscopy reveals interesting variations. A blueshift of up to $\sim$230 km s$^{-1}$ is observed around the east edge of the cold front, where the gas with the lowest specific entropy is found. The region further south inside the cold front shows only a small velocity difference from the BCG; however, its velocity dispersion is enhanced to 400 km s$^{-1}$, implying the development of turbulence. These characteristics indicate that we are observing sloshing motion with some inclination angle following BCG and that gas phases with different specific entropy participate in sloshing with their own velocities, as expected from simulations. No significant evidence for a high-redshift ICM component associated with the subcluster Abell 2319B was found in the region covered by the current Resolve pointings. These results highlight the importance of sloshing and turbulence in shaping the internal structure of Abell 2319. Further deep observations are necessary to better understand the mixing and turbulent processes within the cluster.

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XRISM reveals a variable, multi-phase outflow-inflow structure during the X-ray obscured 2024 outburst of the black hole transient V4641 Sgr

We report the results of a simultaneous X-ray and optical spectroscopy campaign on the Galactic black hole X-ray binary V4641 Sgr, carried out with XRISM and the Seimei telescope during a low-luminosity phase towards the end of its 2024 outburst. Despite a very low X-ray luminosity of $10^{34}$ erg s$^{-1}$, the continuum spectrum is well reproduced by a disk blackbody model with a high inner disk temperature ($1.8$ keV). XRISM/Resolve provides the highest-resolution X-ray spectrum ever obtained from the source, and several strong, narrow emission lines were detected, resolved and characterized at a high significance level. The continuum shape and narrow emission lines both indicate that the inner disk region is obscured by the surrounding high-density gas, and the intrinsic luminosity is several orders of magnitude higher. In the simultaneous optical observation from the Seimei telescope, the line features are largely dominated by the optical companion. Although we detect a clear emission component in H$α$ that could originate from a cold outflow or the disk atmosphere, there are no signs of the strong outflow signatures historically detected in this source. In X-rays, the combination of significantly redshifted ($\sim 700$ km s$^{-1}$) and weakly blueshifted ($\sim-250$ km s$^{-1}$) components, all varying strongly on ks timescales, along with a marginally significant (99.2%) highly blueshifted ($\sim-1200$ km s$^{-1}$) component, indicates a complex, inhomogeneous outflow geometry. This is corroborated by the erratic long-term evolution of the source seen in the complementary X-ray monitoring, and radio detections spanning 3 orders of magnitude.

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XRISM Pre-Pipeline and Singularity: Container-Based Data Processing for the X-Ray Imaging and Spectroscopy Mission and High-Performance Computing

The X-Ray Imaging and Spectroscopy Mission (XRISM) is the seventh Japanese X-ray observatory whose development and operation are in collaboration with universities and research institutes in Japan, the United States, and Europe, including JAXA, NASA, and ESA. The telemetry data downlinked from the satellite are reduced to scientific products using pre-pipeline (PPL) and pipeline (PL) software running on standard Linux virtual machines (VMs) for the JAXA and NASA sides, respectively. OBSIDs identified the observations, and we had 80 and 161 OBSIDs to be reprocessed at the end of the commissioning period and performance verification and calibration period, respectively. The combination of the containerized PPL utilizing Singularity of a container platform running on the JAXA's "TOKI-RURI" high-performance computing (HPC) system and working disk images formatted to ext3 accomplished a 33x speedup in PPL tasks over our regular VM. Herein, we briefly describe the data processing in XRISM and our porting strategies for PPL in the HPC environment.

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Delving into the depths of NGC 3783 with XRISM. I. Kinematic and ionization structure of the highly ionized outflows

We present our study of the XRISM observation of the Seyfert-1 galaxy NGC 3783. XRISM's Resolve microcalorimeter has enabled, for the first time, a detailed characterization of the highly ionized outflows in this active galactic nucleus. Our analysis constrains their outflow and turbulent velocities, along with their ionization parameter ($ξ$) and column density ($N_{\rm H}$). The high-resolution Resolve spectrum reveals a distinct series of Fe absorption lines between 6.4 and 7.8 keV, ranging from Fe XVIII to Fe XXVI. At lower energies, absorption features from Si, S, and Ar are also detected. Our spectroscopy and photoionization modeling of the time-averaged Resolve spectrum uncovers six outflow components, five of which exhibit relatively narrow absorption lines with outflow velocities ranging from 560 to 1170 km/s. In addition, a broad absorption feature is detected, which is consistent with Fe XXVI outflowing at 14,300 km/s (0.05 $c$). The kinetic luminosity of this component is 0.8-3% of the bolometric luminosity. Our analysis of the Resolve spectrum shows that more highly ionized absorption lines are intrinsically broader than those of lower-ionization species, indicating that the turbulent velocity of the six outflow components (ranging from 0 to 3500 km/s) increases with $ξ$. Furthermore, we find that the $N_{\rm H}$ of the outflows generally declines with $ξ$ up to $\log ξ= 3.2$ but rises beyond this point, suggesting a complex ionization structure. The absorption profile of the Fe XXV resonance line is intriguingly similar to UV absorption lines (Ly$α$ and C IV) observed by the HST, from which we infer that the outflows are clumpy in nature. Our XRISM/Resolve results support a "hybrid wind" scenario in which the observed outflows have multiple origins and driving mechanisms. We explore various interpretations of our findings within AGN wind models.

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XRISM Spectroscopy of the Stellar-Mass Black Hole 4U 1630-472 in Outburst

We report on XRISM/Resolve spectroscopy of the recurrent transient and well-known black hole candidate 4U 1630$-$472 during its 2024 outburst. The source was captured at the end of a disk-dominated high/soft state, at an Eddington fraction of $λ_\mathrm{Edd} \sim 0.05~(10 M_{\odot}/M_\mathrm{BH})$. A variable absorption spectrum with unprecedented complexity is revealed with the Resolve calorimeter. This marks one of the lowest Eddington fractions at which highly ionized absorption has been detected in an X-ray binary. The strongest lines are fully resolved, with He-like Fe XXV separated into resonance and intercombination components, and H-like Fe XXVI seen as a spin-orbit doublet. The depth of some absorption lines varied by almost an order of magnitude, far more than expected based on a 10% variation in apparent X-ray flux and ionization parameter. The velocity of some absorption components also changed significantly. Jointly modeling two flux segments with a consistent model including four photoionization zones, the spectrum can be described in terms of highly ionized but likely failed winds that sometimes show red-shifts, variable obscuration that may signal asymmetric structures in the middle and outer accretion disk, and a tentative very fast outflow ($v = 0.026-0.033c$). We discuss the impact of these findings on our understanding of accretion and winds in stellar-mass black holes, and potential consequences for future studies.

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Verification of the Timing System for the X-ray Imaging and Spectroscopy Mission in the GPS Unsynchronized Mode

We report the results from the ground and on-orbit verifications of the XRISM timing system when the satellite clock is not synchronized to the GPS time. In this case, the time is determined by a free-run quartz oscillator of the clock, whose frequency changes depending on its temperature. In the thermal vacuum test performed in 2022, we obtained the GPS unsynchronized mode data and the temperature-versus-clock frequency trend. Comparing the time values calculated from the data and the true GPS times when the data were obtained, we confirmed that the requirement (within a 350 $μ$s error in the absolute time, accounting for both the spacecraft bus system and the ground system) was satisfied in the temperature conditions of the thermal vacuum test. We also simulated the variation of the timing accuracy in the on-orbit temperature conditions using the Hitomi on-orbit temperature data and found that the error remained within the requirement over $\sim 3 \times 10^{5}$ s. The on-orbit tests were conducted in 2023 September and October as part of the bus system checkout. The temperature versus clock frequency trend remained unchanged from that obtained in the thermal vacuum test and the observed time drift was consistent with that expected from the trend.

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Constraining gas motion and non-thermal pressure beyond the core of the Abell 2029 galaxy cluster with XRISM

We report a detailed spectroscopic study of the gas dynamics and hydrostatic mass bias of the galaxy cluster Abell 2029, utilizing high-resolution observations from XRISM Resolve. Abell 2029, known for its cool core and relaxed X-ray morphology, provides an excellent opportunity to investigate the influence of gas motions beyond the central region. Expanding upon prior studies that revealed low turbulence and bulk motions within the core, our analysis covers regions out to the scale radius $R_{2500}$ (670~kpc) based on three radial pointings extending from the cluster center toward the northern side. We obtain accurate measurements of bulk and turbulent velocities along the line of sight. The results indicate that non-thermal pressure accounts for no more than 2% of the total pressure at all radii, with a gradual decrease outward. The observed radial trend differs from many numerical simulations, which often predict an increase in non-thermal pressure fraction at larger radii. These findings suggest that deviations from hydrostatic equilibrium are small, leading to a hydrostatic mass bias of around 2% across the observed area.

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XRISM forecast for the Coma cluster: stormy, with a steep power spectrum

The XRISM Resolve microcalorimeter array measured the velocities of hot intracluster gas at two positions in the Coma galaxy cluster: 3'x3' squares at the center and at 6' (170 kpc) to the south. We find the line-of-sight velocity dispersions in those regions to be sigma_z=208+-12 km/s and 202+-24 km/s, respectively. The central value corresponds to a 3D Mach number of M=0.24+-0.015 and the ratio of the kinetic pressure of small-scale motions to thermal pressure in the intracluster plasma of only 3.1+-0.4%, at the lower end of predictions from cosmological simulations for merging clusters like Coma, and similar to that observed in the cool core of the relaxed cluster A2029. Meanwhile, the gas in both regions exhibits high line-of-sight velocity differences from the mean velocity of the cluster galaxies, Delta v_z=450+-15 km/s and 730+-30 km/s, respectively. A small contribution from an additional gas velocity component, consistent with the cluster optical mean, is detected along a sightline near the cluster center. The combination of the observed velocity dispersions and bulk velocities is not described by a Kolmogorov velocity power spectrum of steady-state turbulence; instead, the data imply a much steeper effective slope (i.e., relatively more power at larger linear scales). This may indicate either a very large dissipation scale resulting in the suppression of small-scale motions, or a transient dynamic state of the cluster, where large-scale gas flows generated by an ongoing merger have not yet cascaded down to small scales.

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AGN outflows and their properties in Mrk 766 as revealed by KOOLS-IFU on the Seimei Telescope

We present the emission-line flux distributions and their ratios, as well as the gas outflow features, of the innermost 2 kpc region of the type 1 Seyfert galaxy Mrk 766, using the Kyoto Okayama Optical Low-dispersion Spectrograph with an optical-fiber integral field unit on the Seimei Telescope. We find that the central region of Mrk 766 is kinematically disturbed, exhibiting asymmetric and radially distributed AGN-driven ionized gas outflows traced by \OIII\ with velocities exceeding 500 \kms. The mass of the ionized gas outflow is estimated to be $10^{4.65-5.95} M_{\odot}$, and the mass outflow rate is $0.14-2.73$ M${\odot}$ yr$^{-1}$. This corresponds to a kinetic power, $\dot{E}_{\rm K}$, of $4.31 \times 10^{40} \ {\rm erg} \ {\rm s^{-1}}< \dot{E}_{\rm K} < 8.62 \times 10^{41} \ {\rm erg} \ {\rm s^{-1}}$, which is equivalent to $0.08\%-1.53\%$ of the bolometric luminosity, $L_{\rm bol}$. This result is consistent with other observed properties of ionized gas outflows, although it is lower than the theoretical predictions in AGN feedback models ($\sim5\%$), implying that ionized gas outflows traced by \OIII\ represent only a minor fraction of the total outflows ejected from the host galaxy. Given the asymmetric and radially distributed outflow signatures observed across the host galaxy within the limited field of view, the maximum distance the outflowing gas has traveled remains an open question.

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Development of the Timing System for the X-Ray Imaging and Spectroscopy Mission

This paper describes the development, design, ground verification, and in-orbit verification, performance measurement, and calibration of the timing system for the X-Ray Imaging and Spectroscopy Mission (XRISM). The scientific goals of the mission require an absolute timing accuracy of 1.0~ms. All components of the timing system were designed and verified to be within the timing error budgets, which were assigned by component to meet the requirements. After the launch of XRISM, the timing capability of the ground-tuned timing system was verified using the millisecond pulsar PSR~B1937+21 during the commissioning period, and the timing jitter of the bus and the ground component were found to be below $15~μ$s compared to the NICER (Neutron star Interior Composition ExploreR) profile. During the performance verification and calibration period, simultaneous observations of the Crab pulsar by XRISM, NuSTAR (Nuclear Spectroscopic Telescope Array), and NICER were made to measure the absolute timing offset of the system, showing that the arrival time of the main pulse with XRISM was aligned with that of NICER and NuSTAR to within $200~μ$s. In conclusion, the absolute timing accuracy of the bus and the ground component of the XRISM timing system meets the timing error budget of $500~μ$s.

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Detection of extended X-ray emission around the PeVatron microquasar V4641 Sgr with XRISM

A recent report on the detection of very-high-energy gamma rays from V4641 Sagittarii (V4641 Sgr) up to ~0.8 peta-electronvolt has made it the second confirmed "PeVatron" microquasar. Here we report on the observation of V4641 Sgr with X-Ray Imaging and Spectroscopy Mission (XRISM) in September 2024. Thanks to the large field of view and low background, the CCD imager Xtend successfully detected for the first time X-ray extended emission around V4641 Sgr with a significance of > 4.5 sigma and > 10 sigma based on our imaging and spectral analysis, respectively. The spatial extent is estimated to have a radius of $7 \pm 3$ arcmin ($13 \pm 5$ pc at a distance of 6.2 kpc) assuming a Gaussian-like radial distribution, which suggests that the particle acceleration site is within ~10 pc of the microquasar. If the X-ray morphology traces the diffusion of accelerated electrons, this spatial extent can be explained by either an enhanced magnetic field (~80 uG) or a suppressed diffusion coefficient (~$10^{27}$ cm$^2$ s$^{-1}$ at 100 TeV). The integrated X-ray flux, (4-6)$\times 10^{-12}$ erg s$^{-1}$ cm$^{-2}$ (2-10 keV), would require a magnetic field strength higher than the galactic mean (> 8 uG) if the diffuse X-ray emission originates from synchrotron radiation and the gamma-ray emission is predominantly hadronic. If the X-rays are of thermal origin, the measured extension, temperature, and plasma density can be explained by a jet with a luminosity of ~$2\times 10^{39}$ erg s$^{-1}$, which is comparable to the Eddington luminosity of this system.

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Container-Based Pre-Pipeline Data Processing on HPC for XRISM

The X-Ray Imaging and Spectroscopy Mission (XRISM) is the 7th Japanese X-ray observatory, whose development and operation are in collaboration with universities and research institutes in Japan, U.S., and Europe, including JAXA, NASA, and ESA. The telemetry data downlinked from the satellite are reduced to scientific products by the pre-pipeline (PPL) and pipeline (PL) software running on standard Linux virtual machines on the JAXA and NASA sides, respectively. We ported the PPL to the JAXA "TOKI-RURI" high-performance computing (HPC) system capable of completing $\simeq 160$ PPL processes within 24 hours by utilizing the container platform of Singularity and its "--bind" option. In this paper, we briefly show the data processing in XRISM and present our porting strategy of PPL to the HPC environment in detail.

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