Takeshi Go Tsuru

We present the XRISM/Resolve spectroscopy of Her X-1 across three X-ray eclipses observed in 2024 September, resolving its iron K complex through the ingress, mid-eclipse, and egress phases. The 5 eV high energy resolution of Resolve enabled us to disentangle and detect all the primary components of the iron K complex: neutral iron fluorescence (Fe K α and K β ) and highly ionized emission lines (Fe XXV He α and Fe XXVI Ly α ). The neutral Fe K α emission is not significantly detected during mid-eclipse, indicating a compact origin near the neutron star. At ingress and egress, the line centroid exhibits red- and blueshifts of ∼200 km s ⁻¹ after correcting for the systemic velocity and the neutron star’s orbital motion. This residual shift corresponds to Keplerian rotation at a characteristic radius of r _disk ∼ 6.6 × 10 ⁶ km, suggesting an association with the outer accretion disk. In contrast, the highly ionized Fe XXV He α and Fe XXVI Ly α lines remain visible during eclipses, indicating an extended origin. Photoionization modeling (SPEX pion model) yields log 10 ( ξ / erg cm s − 1 ) ∼ 3.4 and N _H ∼ 3.1 × 10 ²² cm ⁻² , consistent with the ionized disk wind of Her X-1. Flux-ratio diagnostics constrain the geometric inner boundary of the clumpy disk wind to R in = 3 − 2 + 5 × 1 0 10 cm (1 σ ), consistent with the Compton-heated thermal winds. The inferred mass outflow rate is M ̇ out ≈ 3.2 × 1 0 − 9 M ⊙ yr − 1 (half the supplied mass), consistent with absorption line measurements of the disk wind obtained out of eclipse.

During its performance-verification phase, XRISM observed the M82 galaxy for a net exposure of 207.7 ks, with the ultraluminous X-ray pulsar (ULXP) X-2 included in the field of view. A pulsation search identified a candidate signal with a period close to the previously known value of 1.38727 s, at a significance of 3.15 σ based on Monte Carlo simulations. Using this candidate period, phase-resolved spectral analysis was performed with the high spectral resolution of Resolve. The spectra suggest that, if the candidate pulsation is real, the Fe K α emission line during the pulse-peak phase has a larger width ( 3 6 − 13 + 60 eV) than that during the remaining phase, with a significance exceeding 3 σ . This suggests that at least a fraction of the Fe K α emission is associated with the ULXP system. The observed width corresponds to a velocity dispersion of ( 1 . 7 − 0.6 + 2.8 ) × 1 0 3 km s ⁻¹ , which is too large to be explained by motions in the companion-star atmosphere. The rise time of the pulsation constrains the line-emitting region to be smaller than 6.3 × 10 ⁴ km, suggesting an origin in the accretion flow. This work demonstrates the capability of XRISM Resolve for pulsation-resolved high-resolution spectroscopy of ULXPs.

The supermassive binary system, η Carinae, is experiencing enormous wind-driven mass loss at a rate unparalleled in the rest of the Galaxy. Their wind–wind collision (WWC) continuously produces shock heated, X-ray-emitting plasmas. The XRISM X-ray observatory observed the system in 2023 and 2024 when the X-ray emission began to increase toward periastron passage in 2025. This paper reports unprecedentedly high-resolution X-ray spectra in the Fe K α band between 6.2 and 7.1 keV, obtained with the Resolve X-ray microcalorimeter. The hydrogen-like (Ly α ) and helium-like (He α ) lines reveal three velocity components. Two of them are broadened with maximum velocities of 2000–3000 km s ⁻¹ , likely originating from the postshock companion wind. The other is relatively narrow, with a Gaussian broadening of only ∼290 km s ⁻¹ in 1 σ , which may originate from the postshock companion wind at the WWC stagnation point or penetrating the primary wind. The Fe fluorescent lines exhibit a moderate blueshift and broadening with velocities at 100–200 km s ⁻¹ , consistent with the primary wind’s velocity field. The spectra also confirm a Compton shoulder of the He α line complex for the first time. Both fluorescing and scattering spectral profiles indicate that the binary system is seen from the companion side during these observations. The flux ratio of the Compton-scattering emission to the fluorescent line suggests substantial hydrogen depletion of the primary wind, expected from CNO-cycled hydrogen nuclear fusion gas.

The XRISM/Resolve microcalorimeter directly measured the gas velocities in the core of the Virgo Cluster, the closest example of active galactic nucleus (AGN) feedback in a cluster. This proximity allows us to resolve the kinematic impact of feedback on scales down to 5 kpc. Our spectral analysis reveals a high velocity dispersion of σ v = 26 2 − 38 + 45 km s ⁻¹ near the AGN, which steeply declines to ∼60 km s ⁻¹ between 5 and 25 kpc in the northwest direction. The observed line-of-sight bulk velocity in all regions is broadly consistent with the central galaxy, M87, with a mild trend toward blueshifted motions at larger radii. Systematic uncertainties have been carefully assessed and do not affect the measurements. The central velocities, if attributed entirely to isotropic turbulence, correspond to a transonic intracluster medium at sub-6 kpc scales with 3D Mach number 0 . 69 -0.11 +0.14 and a nonthermal pressure fraction of 21 -5 +7 % . Simple models of weak shocks and sound waves and calculations assuming isotropic turbulence both support the hypothesis that the velocity field reflects a mix of shock-driven expansion and turbulence. Compared to other clusters observed by XRISM to date, M87’s central region stands out as the most kinematically disturbed, exhibiting both the highest velocity dispersion and the largest 3D Mach number, concentrated at the smallest physical scales.

We stack 3.75 Ms of early XRISM Resolve observations of 10 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 3 σ upper limit on the m _s ∼ 7.1 keV DM particle decay rate (which corresponds to an E = 3.55 keV emission line) of Γ ∼ 1.0 × 10 ⁻²⁷ s ⁻¹ . This upper limit is 3–4 times lower than the one derived by Hitomi Collaboration from the Perseus observation but still 5 times higher than the XMM-Newton detection reported by E. Bulbul et al. in the stacked cluster sample. XRISM Resolve, with its high spectral resolution but 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.

We report on new Chandra ACIS-I observations of the X-ray knots located in the western and eastern lobes of W50 associated with the parsec-scale jets of the Galactic microquasar SS 433. These knots are likely counterparts of the recently detected very-high-energy ( E > 100 GeV) gamma-ray emission by HAWC and HESS. These findings, together with the ultrahigh-energy signal recently reported by the LHAASO Collaboration, have established the SS 433/W50 system as a unique jet-driven PeVatron candidate. Combining new and archival Chandra data, we perform the first proper motion search of the X-ray knot structures over a time interval spanning approximately 20 yr. We found no statistically significant motion of these knots at the 3 σ confidence level, and place an upper limit of c (5800–9800 km s ⁻¹ ) for the speed of the innermost knots at an assumed distance d = 5.5 kpc. Combined with the velocities reported in the literature, the upstream speed in the shock rest frame would reach several 10 ⁴ km s ⁻¹ , suggesting that highly efficient particle acceleration, approaching the Bohm limit, is occurring. The absence of significant motion of the knots suggests the presence of a standing recollimation shock, formed by the balance between the jet pressure and the external pressure. This interpretation is consistent with the expected occurrence of such shocks at 20–30 pc from SS 433, matching the location of the observed knots.

The dynamics of the intracluster medium (ICM), the hot plasma that fills galaxy clusters, are shaped by gravity-driven cluster mergers and feedback from supermassive black holes (SMBHs) 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, and 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 10 measurements below the median simulated values by a factor of 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 (NCC) 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 NCC 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 NCC clusters will clarify if there is a systematic tension in the gravity-dominated regime as well.