arXiv subjects

Shinya Yamada

Publications and source records attributed to Shinya Yamada.

At least 19 recordsLinked to original sources

arXiv2026

Vigorous turbulence driven by quasar-mode feedback in a cluster core

Quasars are among the most luminous objects. They are powered by accretion onto supermassive black holes. They are thought to impact cosmological evolution primarily through energetic winds, known as quasar-mode feedback, yet the efficiency and spatial extent of this process remain poorly constrained. Here we present X-Ray Imaging and Spectroscopy Mission (XRISM) observations of H1821+643---the nearest galaxy cluster with a central quasar (redshift z = 0.297)---which was a rare opportunity to directly probe quasar-mode feedback in the intracluster medium. High-resolution spectroscopy reveals exceptionally broadened Fe XXV emission lines from the intracluster medium, with a velocity dispersion of approximately 300 km/s, far exceeding values observed in nearby cluster cores. These lines originate predominantly at radii of 20-100 kpc from the centre. Assuming that turbulence from a quasar-driven shock led to the broadening of the lines, the energy injected by the quasar beyond galactic scales ($\gtrsim$20 kpc) is estimated to be $\gtrsim$1-10% of its radiative energy. Notably, this feedback efficiency exceeds previous multiwavelength estimates by orders of magnitude ($\lesssim$0.01%) and reaches the levels required by the latest cosmological hydrodynamical simulations. This finding of vigorous turbulence indicates that quasar-mode feedback plays a central role in regulating galaxy and cluster evolution at high redshift.

astro-ph.GA↗

arXiv2026

Chandra X-Ray Imaging and Spatially Resolved Spectroscopy of SN 1987A: Energy-Dependent Morphology of the Equatorial Ring

We present a systematic imaging and spatially resolved spectral study of SN 1987A using Chandra observations obtained between 1999 and 2025. By combining multiepoch ACIS and HETG data, we investigate the long-term evolution of the remnant in both the soft and hard X-ray bands. To characterize the radial structure, we model the projected emission with a torus profile and derive its radius and width on the image plane. We find an energy dependence in the ring morphology: while the soft and hard bands exhibit similar structures at early epochs, the soft-band emission becomes systematically broader than the hard-band emission after the early 2010s. Furthermore, when considering the radius and width together, the soft-band emission shows an inward extension, suggesting an increasing contribution from interior and/or high-latitude emission components. The flux evolution of the Fe K line is consistent with previous XMM-Newton results, and we detect its presence already in earlier epochs (~2007-2009) using combined Chandra spectra. Spatially resolved analysis further indicates that the Fe K emission is enhanced in the eastern region. These results provide a unified view of the long-term morphological and spectral evolution of SN 1987A and highlight the emergence of energy-dependent radial structure as a key feature in its late-time evolution.

astro-ph.HE↗

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 $5 \times 10^{-6}$-$1 \times 10^{-5}\ M_{\odot}\ {\rm yr}^{-1}$.

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arXiv2026

XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 -- Orbital and Short-Term Variability of Iron Absorption

We present the first high-resolution spectroscopy of the black hole high-mass X-ray binary Cygnus X-1 with XRISM, including orbital-phase-resolved analyses and tentative evidence of short-term variability in the Fe-K band on second timescales. Using data from the Performance Verification phase in April 2024, we analyzed spectral variability across orbital phases with the Resolve microcalorimeter and the Xtend CCD imager. The unprecedented resolution of Resolve reveals variability in highly ionized Fe absorption lines. The absorption features show orbital-phase-dependent variability in column density, ionization state, and blueshifted velocity, suggesting structural variations in the focused stellar wind along the line of sight. We also find indications of subtle broadening of the neutral Fe emission profile. In addition, intensity-sorted spectroscopy during dip phases suggests possible variability on timescales of a few seconds in the absorption features, consistent with cooler, denser and lower-ionized gas clumps. Although the statistical significance is limited, these results hint that the stellar wind and the X-rays from the accretion disk around the black hole may interact on timescales as short as a few seconds. These XRISM results constrain wind-fed accretion in Cyg X-1 and highlight Resolve's capability to probe plasma environments in high-mass X-ray binaries.

astro-ph.HE↗

arXiv2026

Broad-band High-Energy Resolution Hard X-ray Spectroscopy using Transition Edge Sensors at SPring-8

We have succeeded in operating a transition-edge sensor (TES) spectrometer and evaluating its performance at the SPring-8 synchrotron X-ray light source. The TES spectrometer consists of a 240 pixel National Institute of Standards and Technology (NIST) TES system, and 220 pixels are operated simultaneously with an energy resolution of $4$~eV at 6~keV at a rate of about 1~c/s/pixel. The tolerance for high count rates is evaluated in terms of energy resolution and live time fraction, leading to an empirical compromise of about 2 x 10^3 c/s/all pixels with an energy resolution of 5 eV at 6 keV. By utilizing the TES's wide-band spectroscopic capability, simultaneous multi-element analysis is demonstrated for a standard sample. We conducted X-ray absorption near-edge structure (XANES) analysis in fluorescence mode using the TES spectrometer. The excellent energy resolution of the TES enabled us to detect weak fluorescence lines from dilute samples and trace elements that have previously been difficult to resolve due to the nearly overlapping emission lines of other dominant elements. The neighboring lines of As K alpha and Pb L alpha2 of the standard sample were clearly resolved and the XANES of Pb L alpha2 was obtained. Moreover, the X-ray spectrum from the small amount of Fe in aerosols was distinguished from the spectrum of a blank target, which helps us to understand the targets and the environment. These results are the first important step for the application of high resolution TES-based spectroscopy at hard X-ray synchrotron facilities.

astro-ph.IM↗

arXiv2026

XRISM High-Resolution X-ray Spectroscopy of Cygnus X-1 -- highly ionized Iron absorption structures

We present the first high-resolution X-ray spectral analysis of Cygnus X-1 using XRISM. The observation was carried out from April 7 to 10, 2024, covering the orbital phase range 0.65--0.17 during its low/hard state. Taking advantage of the exceptional energy resolution of the Resolve instrument, we examined highly ionized iron absorption lines and characterized the ionization states, column densities, and line-of-sight velocities of the absorbing plasma. Spectral analysis revealed an ionization parameter of approximately 3, column densities of a few times 10^21 cm^-2, and a blueshifted velocity of approximately 100 km s^-1. The observation was divided into two phases: before and after orbital phase phi_orb = 0.9, corresponding to non-dipping and dipping intervals. While only weak absorption features were present before phi_orb = 0.9, strong absorption by He-like and H-like Fe appeared during the dipping phase. We measured equivalent widths of 2.3 eV, 0.4 eV, and 1.2 eV for He-like Fe K-alpha, and H-like Ly-alpha1 and Ly-alpha2, respectively, demonstrating the capability of XRISM Resolve to securely detect narrow absorption features of only a few eV. These measurements trace the motion of the absorbing material and offer insight into the kinematics and spatial distribution of the wind in the vicinity of the black hole. These findings enhance our understanding of wind-fed accretion in Cygnus X-1 and highlight the importance of continued high-resolution X-ray observations to further constrain the physical properties of winds and accretion flows in high-mass X-ray binaries.

astro-ph.HE↗

arXiv2026

XRISM spectroscopy of a crowded Galactic center region -- I. Disentangling the sources in the field of view

The Galactic center is a complex and crowded region hosting the supermassive black hole Sgr A*, numerous accreting compact objects, and diffuse X-ray emission. This paper presents the first in a series of studies analyzing the XRISM observation of the X-ray transient MAXI J1744-294/Swift J174540.2-290037, located $\sim18''$ from Sgr A*. The observation, conducted in March 2025, along with XMM-Newton and NuSTAR coverage, aimed to investigate the Fe emission features of MAXI J1744-294 during its outburst. However, the region surrounding the source is heavily contaminated by X-ray emission from various diffuse and point sources, including strong line contributions from the supernova remnant Sgr A East and the Galactic center X-ray emission (GCXE). Additionally, the nearby neutron star low-mass X-ray binary (NS-LMXB) AX J1745.6-2901 was also in outburst during the XRISM observation, further complicating the spectral analysis. This study focuses on disentangling the contributions of these overlapping sources by robustly modeling the background contamination and spatial-spectral mixing. We describe the methodologies, region selection, and data reduction techniques applied to the different instruments. Two complementary approaches -- empirical and physical modeling -- are employed to characterize diffuse emission and point-source contributions. The results provide a foundation for the detailed spectral analysis of MAXI J1744-294, AX J1745.6-2901, and the surrounding interstellar medium (ISM), which will be presented in subsequent papers. This study highlights the challenges and robust solutions for analyzing XRISM/Resolve data from crowded regions in conjunction with other X-ray telescope data.

astro-ph.HE↗

arXiv2026

Narrow iron- and nickel-K absorption lines from the eclipsing low-mass X-ray binary AX~J1745.6$-$2901

We report the presence of a highly ionized absorber in the transient, eclipsing low-mass X-ray binary AX J1745.6-2901, observed from Feb. 26 to 29, 2024 with XRISM's Resolve and Xtend instruments. During a soft/high state without dips, Resolve's high spectral resolution (E/dE ~ 1000, full width at half maximum) revealed narrow velocity widths (sigma ~ 110 km/s) for Fe XXVI and Ni XXVIII lines, even with low photon statistics. These widths are consistent with binary orbital motion. The observed modest blueshift velocity (~160 km/s) indicates that the absorber is located sufficiently far from the neutron star (> 10^9 cm), so that gravitational redshift effects are not dominant. On the other hand, broad-band spectral analysis using a photoionized plasma model applied to the Xtend data constrains the absorber to lie within a radius of < 10^9.5 cm, as inferred from the upper limits of the best-fit ionization parameter (log xi ~ 4.4) and the large column density (~ 1.6 x 10^24 cm^-2). At this distance, the observed outward velocity of the absorber is about an order of magnitude smaller than the escape velocity from the neutron star.

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

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↗

arXiv2025

XRISM High-resolution Spectroscopy of SS 433: Evidence of Decreasing Line-of-Sight Velocity Dispersion along the Jet

We report on the jet structure in SS 433 based on X-ray high resolution spectroscopy with the XRISM/Resolve. The source was observed over 5 days covering both inside and outside an eclipse of the compact object by the companion star. Doppler-shifted, ionized Fe and Ni K emission lines were resolved, as well as lower-energy lines including Si and S K lines. Time-resolved spectral analysis showed that Fe and Ni K line widths were $1020 \pm 40$ km s$^{-1}$ (corresponding the 1$\sigma$ width) in the eclipse phase, gradually increased during the egress, and reached $1740 \pm 30$ km s$^{-1}$ outside the eclipse. A time-averaged spectrum outside the eclipse confirmed that the Fe and Ni K lines in 5.5-9 keV are significantly broader than the Si and S K$\alpha$ emission lines in 2--4 keV. Specifically, the width in 5.5-9 keV was measured to be $1900 \pm 80$ km s$^{-1}$, whereas the width in 2-4 keV is $1300^{+300}_{-400}$ km s$^{-1}$ for the approaching (blueshifted) jet component. These results indicate that radial velocity dispersion of the jet plasma in SS 433 decreases as it moves outward. We interpret this variation as progressive jet collimation along its axis, as suggested by Namiki et al. (2003), or a decrease in turbulence in the jet plasma flow within the X-ray emitting region. We also detected a clear difference in velocity dispersion between the approaching and receding (redshifted) jet components in the 5.5-9 keV band outside eclipse. The receding jet exhibited a smaller velocity dispersion ($1400 \pm 200$ km s$^{-1}$) than the approaching jet. Since the observation was conducted when the approaching jet was tilted toward the observer, this may suggest that the receding jet was more extensively occulted by the accretion disk.

astro-ph.HE↗

arXiv2025

Decadal brightening in the northeastern non-thermal filament of Cassiopeia A

We present the decadal brightening of non-thermal emission flux in the northeastern filament of the young supernova remnant Cassiopeia A (Cas A), which highlights dynamic processes in the forward shock. This filament, characterized by the highest particle acceleration rate among Cas A's outer shells, offers an exceptional opportunity to investigate underlying astrophysical mechanisms. Since 2000, the non-thermal flux has increased by several tens of percent before plateauing, while the spectral shape has remained largely unchanged. Over the past two decades, the filament's morphology has evolved significantly, splitting into two distinct sections. Detailed analysis reveals contrasting behaviors: one section shows a flux increase followed by saturation, while the other maintains a steady flux. These differences likely arise from nonlinear effects, including magnetohydrodynamic interactions influenced by magnetic field orientation, interactions with surrounding material, and complex fluid dynamics associated with young supernova remnants. The localized evolution of this filament, captured with high spatial resolution, provides critical insights into the temporal dynamics of non-thermal particles and the generation of cosmic rays from asymmetric supernova explosions.

astro-ph.HE↗

arXiv2025

First Detection of X-ray Polarization and Its Short-term Increase Pre- and Post-Eclipse in HMXB 4U 1700-377

We report the first statistically significant detection of X-ray polarization from the high-mass X-ray binary (HMXB) 4U 1700-377, observed using the Imaging X-ray Polarimetry Explorer (IXPE). A polarization degree exceeding 10% was detected above 5 keV, placing it among the highest polarization observed in HMXBs to date. The observation was conducted over a full orbital period of the binary system, during which several sporadic and instantaneous flares were detected. We identify a clear correlation between the polarization degree and orbital phase, with the highest polarization occurring just before and after the eclipse, reaching over 20% for a few tens of ks. These results suggest that the scattering medium responsible for the observed polarization is spatially localized between the compact object and the O-type companion star, likely created by large-scale inhomogeneities in the stellar wind and its interaction with the compact star's emission. We also explore the roles of disk winds and orbital reflection in the observed polarization variability. While both mechanisms contribute to the polarization, the substantial increase in polarization before and after the eclipse cannot be fully explained by these models alone, suggesting that the involvement of additional factors. The properties of the X-ray polarization observed by IXPE provide new insights into the accretion processes, X-ray emission, and wind structure in 4U 1700-377, advancing our understanding of their complex environments and the nature of the compact objects within.

astro-ph.HE↗

arXiv2025

Arcsecond-Scale X-ray Imaging and Spectroscopy of SS 433 with Chandra HETG

We present a spatial and spectral analysis of arcsecond-scale X-ray emission in SS 433 using zeroth-order data from Chandra High-Energy Transmission Grating (HETG) observations. The analysis is based on 24 observations acquired between 1999 and 2024, comprising a total exposure of $\sim$850 ks and covering a wide range of orbital and precessional phases. Among these, the $\sim$140 ks observation from 2014 was analyzed in detail for this study. This data provides the best statistics and was taken when the jets were nearly perpendicular to the line of sight and the accretion disk was eclipsed. By applying an energy-dependent subpixel event repositioning algorithm and the Richardson-Lucy deconvolution, we enhanced the spatial resolution and revealed eastern and western knot-like structures at a distance of $\sim$1.7 arcsec ($\sim 10^{17}$ cm) from the core. These features are consistent with the kinematic precession model, and the positions of the knots suggest that they were ejected approximately 200 days prior to the observation. A comparison with VLA radio data obtained at a similar precessional phase shows that the X-ray emission extends east-west on a scale comparable to that of the radio emission. While the core is bright in both X-rays and radio, the brightness contrast between the knots and the core is smaller in X-rays than in radio. Spatially resolved spectroscopy indicates that prominent Fe lines in the core X-ray spectrum are well explained by thermal plasma emission. In contrast, Fe lines are not evident in the outer regions after accounting for potential core contamination, suggesting a dominant contribution from non-thermal processes. These findings imply that the arcsecond-scale X-ray structures may vary observationally with viewing conditions or precessional phase, but likely reflect a relatively stable jet-driving mechanism operating within the SS 433 system.

astro-ph.HE↗

arXiv2025

Quantum Machine Learning for Identifying Transient Events in X-ray Light Curves

We investigate whether a novel method of quantum machine learning (QML) can identify anomalous events in X-ray light curves as transient events and apply it to detect such events from the XMM-Newton 4XMM-DR14 catalog. The architecture we adopt is a quantum version of the long-short term memory (LSTM) where some fully connected layers are replaced with quantum circuits. The LSTM, making predictions based on preceding data, allows identification of anomalies by comparing predicted and actual time-series data. The necessary training data are generated by simulating active galactic nucleus-like light curves as the species would be a significant population in the XMM-Newton catalog. Additional anomaly data used to assess trained quantum LSTM (QLSTM) models are produced by adding flares like quasi-periodic eruptions to the training data. Comparing various aspects of the performances of the quantum and classical LSTM models, we find that QLSTM models incorporating quantum superposition and entanglement slightly outperform the classical LSTM (CLSTM) model in expressive power, accuracy, and true-positive rate. The highest-performance QLSTM model is then used to identify transient events in 4XMM-DR14. Out of 40154 light curves in the 0.2--12 keV band, we detect 113 light curves with anomalies, or transient event candidates. This number is $\approx$ 1.3 times that of anomalies detectable with the CLSTM model. By utilizing SIMBAD and four wide-field survey catalogs made by ROSAT, SkyMapper, Pan-STARRS, and WISE, no possible counterparts are found for 12 detected anomalies.

astro-ph.HE↗

arXiv2025

XRISM insights for interstellar Sulfur

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 SII 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 SII Kbeta line centroid at 2470.8 +/- 1.1 eV after including systematic uncertainties. We also find that the most recently published high resolution SII 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_7S_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% +/- 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.

astro-ph.GA↗

arXiv2025

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 $\lambda_\mathrm{Edd} \sim 0.05~(10 M_{\odot}/M_\mathrm{BH})$. 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.

astro-ph.HE↗

arXiv2025

High count rate effects in event processing for XRISM/Resolve x-ray microcalorimeter: II. Energy scale and resolution in orbit

The Resolve instrument on the X-ray Imaging and Spectroscopy Mission (XRISM) uses a 36-pixel microcalorimeter designed to deliver high-resolution, non-dispersive X-ray spectroscopy. Although it is optimized for extended sources with low count rates, Resolve observations of bright point sources are still able to provide unique insights into the physics of these objects, as long as high count rate effects are addressed in the analysis. These effects include {the loss of exposure time for each pixel}, change on the energy scale, and change on the energy resolution. To investigate these effects under realistic observational conditions, we observed the bright X-ray source, the Crab Nebula, with XRISM at several offset positions with respect to the Resolve field of view and with continuous illumination from {$^{55}$Fe sources} on the filter wheel. For the spectral analysis, we excluded data where exposure time loss was too significant to ensure reliable spectral statistics. The energy scale at 6 keV shows a slight negative shift in the high-count-rate regime. The energy resolution at 6 keV worsens as the count rate in electrically neighboring pixels increases, but can be restored by applying a nearest-neighbor coincidence cut (``cross-talk cut''). We examined how these effects influence the observation of bright point sources, using GX 13+1 as a test case, and identified an eV-scale energy offset at 6 keV between the inner (brighter) and outer (fainter) pixels. Users who seek to analyze velocity structures on the order of tens of km~s$^{-1}$ should account for such high count rate effects. These findings will aid in the interpretation of Resolve data from bright sources and provide valuable considerations for designing and planning for future microcalorimeter missions.

astro-ph.IM↗