Camille M. Diez

Context. Galactic high-mass X-ray binaries (HMXBs) are important systems for studying accretion mechanisms onto compact objects and for investigating the complex stellar winds of massive stars. In particular, HMXBs that host a neutron star allow us to reveal the structure of the accreted material in X-ray pulsars and consequently to investigate how matter behaves under extreme conditions of pressure and density. These are major scientific goals for XRISM and NewAthena . Aims. Here we report on the first out-of-eclipse XMM-Newton observation of the HMXB 4U 1538−52, complemented by NuSTAR coverage. Our campaign aimed to investigate stellar-wind variability and continuum changes with high-resolution spectroscopy at a critical orbital phase: when the neutron star is in inferior conjunction. Methods. Thanks to simultaneous observations covering both soft and hard X-rays, we obtain the most detailed X-ray view of the accreted material in 4U 1538−52 to date. In particular, we perform time-resolved spectroscopy down to the pulse period of the neutron star to highlight wind clumping properties and accretion structures. Results. In this dataset, we observe a bright flare reaching ∼10 ³⁷ erg s ⁻¹ probably induced by the accretion of a 10 ²⁰ g clump, followed by a luminosity dip forming a heartbeat-like episode. This event is followed by three local absorption peaks with local variability of the order of the pulse period and a gradual hardening of the underlying spectrum throughout the observation. This could indicate the presence of both small-scale and large-scale overdense structures in the vicinity of the neutron star, which can be attributed to clumps and filamentary structures embedded in the accretion wake. These observational evidences are further supported and reproduced by 3D hydrodynamic simulations.

We report on the high-resolution X-ray spectroscopy of the Be/X-ray binary pulsar (BeXBP) 1A 1118−61 during the outburst in 2026 January–February with X-Ray Imaging and Spectroscopy Mission (XRISM)/Resolve. We have successfully resolved the structure of neutral Fe K α emission lines (including K α ₁ and K α ₂ ) and found that they consist of two distinct components with line widths of σ ∼ 2 eV (∼100 km s ⁻¹ ) and σ ∼ 40 eV (∼2000 km s ⁻¹ ). The Resolve data also allow us to perform pulse-phase-resolved spectroscopy. For the narrow ( σ ∼ 2 eV) component, the line flux and equivalent width vary with the pulse phase, whereas its centroid energy and width do not. In contrast, for the broad ( σ ∼ 40 eV) line component, the centroid energy and width show pulse-phase dependence, while the line flux and equivalent width do not show significant changes. These results suggest that the broad Fe K α emission likely originates from the inner region of the accretion disk truncated near the magnetospheric radius, while the narrow Fe K α emission may arise from the Be star and/or its surrounding circumstellar disk.

We report results from a multi-mission observational campaign of the transient X-ray pulsar 2S 1417−624 during its 2025 outburst, using data from NICER, IXPE, and NuSTAR. Phase-averaged and phase-resolved spectroscopy with NICER and NuSTAR reveal that a typical broken power-law model with a high-energy cutoff describes the broadband spectra well. Several spectral parameters, however, show clear and systematic modulations with pulse phase, indicating variations in the physical conditions of the emitting plasma over the neutron star’s rotation. IXPE provides the first polarimetric measurements of this source, yielding a phase-averaged polarization degree (PD) of 4.8 ± 1.2% and a polarization angle (PA) of 17° ±7°, both quoted at the 1 σ confidence level. Fitting the phase-resolved PA with the rotating vector model (RVM) gives a magnetic obliquity of θ = 69 ₋₂₉ ⁺¹³ deg, indicating a significantly inclined magnetic geometry that may approach a quasi-orthogonal configuration. In addition, using the unbinned photon-by-photon method, we obtain a PD of 5.9 ± 1.2% across the pulse phase, together with a pulsar geometry consistent with that inferred from the binned analysis, assuming the variable PA predicted by the RVM. A simultaneous RVM fit across the three energy bands, 2–5 keV, 5–6 keV, and 6–8 keV, provides the strongest constraints on the geometrical parameters, yielding θ = 84 ₋₆ ⁺⁴ deg. Together, these findings demonstrate pronounced phase-dependent spectral and polarization variability, offering valuable constraints on the geometry and emission processes within the accretion region of this transient X-ray pulsar.

Context. Pulse profiles probe the emission geometry of accreting X-ray pulsars, but their observed shapes may depend on instrumental response and observational setup. The pulsed fraction spectrum provides a compact spectro-timing observable that can both trace localized spectral features and serve as a quantitative cross-calibration diagnostic. Aims. We assess the consistency of energy-resolved pulse profiles obtained with simultaneous XMM-Newton/EPIC-pn and NuSTAR/FPM observations of Vela X-1 and investigate the broadband pulsed fraction spectrum as a diagnostic of spectral features from 1 to 70 keV. Methods. We constructed energy–phase matrices for both instruments and derived pulsed fraction spectra after carefully accounting for instrumental and observational effects. We quantified the residual systematics in the overlapping 3–10 keV band. We then modeled the broadband pulsed fraction spectra phenomenologically and searched for timing signatures of spectral features. Results. After correcting for instrumental effects, the pulsed fraction spectra derived strictly over the common exposure intervals of the two instruments agree within 5% in their overlapping 3–10 keV range. Remaining discrepancies larger than 5% are confined to the iron-line region and can be attributed to the different energy resolutions of the two instruments. The broadband pulsed fraction spectrum reveals significant localized features corresponding to known emission lines in the soft band and to the fundamental and harmonic cyclotron resonant scattering features at ∼25 and ∼55 keV. An orbital-phase-resolved modeling of the pulsed fraction spectrum of EPIC-pn shows that the soft band features strongly depend on the value of the equivalent absorption column, with emission line signatures becoming progressively suppressed during highly absorbed intervals. Conclusions. The pulsed fraction spectrum serves both as a quantitative cross-calibration diagnostic and as a powerful spectro-timing diagnostic. Its modeling provides independent constraints on spectral features, complementing traditional phase-averaged spectroscopy.

We present a comprehensive analysis of the X-ray spectrum of the highly obscured high-mass X-ray binary IGR J16318−4848 based on ∼250 ks Chandra/HETGS observations covering different orbital phases. We detected a strong narrow Fe K α emission line and interpret our finding as the iron line originating in the stellar wind close to the compact object. We tentatively identify a Compton shoulder associated with the Fe K α line. The ratio of the Compton-shoulder flux to that of the Fe K α core exhibits orbital-phase variability, reaching a maximum of ∼10% around orbital phase ϕ _orb ≃ 0.33. In addition, we do not detect ionized lines, implying that the plasma in the system is predominantly cold. We preliminarily report that the Fe K α line centroid exhibits an orbital modulation with an amplitude of 167 ± 32 km s ⁻¹ , adopting the best-known circular orbit in the source. This study presents the first detailed view of the high-resolution X-ray spectra of IGR J16318−4848 across different orbital phases, providing timely context for the newly taken XRISM observations of the source.

We report on a pair of X-ray Multi-Mirror Mission (XMM-Newton) observations of the Supergiant X-ray binary 4U 1909+07, which were performed on 2021 October 3 and 8, respectively. We measure the neutron star rotation period in each observation to be ∼602.62 s. This continues a long spin-up trend that has persisted since 2001 where the neutron star spin period was found to be ∼604.66 s. In our timing analysis, we observe strong variations in the amplitude of the 1–10 keV pulse profile as a function of time, and for the first time, we find a low flux interval extending for a single pulse period in which pulsations are no longer detected. We interpret this low flux interval as a pulse dropout similar to those observed in Vela X-1 and GX 301-2, which were each explained by a low-density cavity in the wind driving the propeller effect. In our time-resolved spectral analysis, we observed the spectral continuum, which can be described as an absorbed power law modified by a high-energy cutoff, to significantly soften during the pulse-dropout phase. No evidence of an increasing absorption column density was found. The observed softening in 4U 1909+07 also supports an interpretation that the observed pulse dropout may be driven by the propeller effect, but the quasi-spherical settling accretion regime cannot be ruled out.

Using XRISM/Resolve 439 ks time-averaged spectra of the well-known Seyfert-1.5 active galactic nucleus (AGN) in NGC 3783, we investigated the nature of the Fe K α emission line at 6.4 keV, the strongest and most common X-ray line observed in AGNs. Even the narrow component of the line is resolved with evident Fe K α ₁ (6.404 keV) and K α ₂ (6.391 keV) contributions with a 2:1 flux ratio, fully consistent with a neutral gas with negligible bulk velocity. The narrow and intermediate-width components have a full width at half maximum of 350 ± 50 km/s and 3510 ± 470 km/s, respectively, suggesting that they arise in the outer disk/torus and/or broad line region. We detect a 10% excess flux around 4–7 keV that is not described well by a symmetric Gaussian line but is consistent with a relativistically broadened emission line. In this study we took the simplest approach, modelling the asymmetric line as a single emission line (assuming neutral, He-like, or H-like iron) convolved with a relativistic disk line model. As expected, the inferred inclination angle ( i ) is highly sensitive to the assumed ionisation state and ranges between 17 and 44°. This model also constrains the black hole spin via the extent of the red wing: the required gravitational redshift in the fitted disk-line profile disfavours a non-spinning (Schwarzschild) black hole. The derived inner radius is close to the radius of the innermost stable circular orbit ( r _ISCO ) and is strongly correlated with the black hole spin. To better constrain the spin, we fixed the inner radius to r _ISCO and derived a lower limit on the spin of a ≥ 0.29 at the 3 σ confidence level. A Compton shoulder is detected in our data as well as a 2–3 σ detection of the Cr K α and Ni K α lines.

The 2024 X-ray/UV observation campaign of NGC 3783, led by XRISM, revealed the launch of an ultrafast outflow (UFO) with a radial velocity of 0.19 c (57 000 km s ⁻¹ ). This event is synchronized with the sharp decay, within less than half a day, of a prominent soft X-ray/UV flare. Accounting for the look-elsewhere effect, the XRISM Resolve data alone indicate a low probability of 2 × 10 ⁻⁵ that this UFO detection is due to random chance. The UFO features narrow H-like and He-like Fe lines with a velocity dispersion of ∼1000 km s ⁻¹ , suggesting that it originates from a dense clump. Beyond this primary detection, there are hints of weaker outflow signatures throughout the rise and fall phases of the soft flare. Their velocities increase from 0.05 c to 0.3 c over approximately three days, and they may be associated with a larger stream in which the clump is embedded. The radiation pressure is insufficient to drive the acceleration of this rapidly evolving outflow. The observed evolution of the outflow kinematics instead closely resembles that of solar coronal mass ejections, implying magnetic driving and, conceivably, reconnection near the accretion disk as the likely mechanisms behind both the UFO launch and the associated soft flare.

Context. Vela X-1 is a well-studied accreting X-ray pulsar, with a distinctive pulse profile that has been found to be very similar in different observations spread out over decades. On the other hand, significant variations down to the timescale of individual pulses have been observed. The physical mechanisms leading to the energy-resolved pulse profile and its variations are not fully understood. Long, uninterrupted observations of Vela X-1 with XMM-Newton in 2000, 2006, and 2019 at different orbital phases, allow us to study variations of the pulse properties in the soft X-ray range on all timescales in detail. Aims. We aim to characterize and quantify the variations of pulse profiles and individual pulse cycles on all timescales probed, and to identify possible factors driving the observed variations on these timescales. Methods. We generated consistent energy-resolved pulse profiles for each observation, as well as profiles built from subsets of individual pulse cycles selected by time, flux, or similarity to the mean profiles. We identified five pulsed phases based on the profile morphology and hardness, and examined the relative contributions over time. To quantify short-timescale variability, we compared individual pulse cycles with synthetic light curves derived from scaled versions of the average profiles. Results. The pulse profile of Vela X-1, when averaged over many pulse cycles, remains remarkably stable, as expected. The most prominent variations between epochs are attributable to changes in absorption. Residual systematic differences are primarily flux-dependent, with profiles showing less variability at higher flux levels. On shorter timescales, most individual pulse cycles resemble the average profile, even though significant, sporadic deviations are also present.

Context. High-mass X-ray binaries (HMXBs) can serve as useful laboratories for exploring the behaviour of accreted matter onto compact objects and for probing the complex wind environments of massive stars. These investigations are essential for understanding stellar life cycles and the dynamics of the Milky Way, and they are prominent topics in the science cases for XRISM and NewAthena . Aims. We report, for the first time, on a XRISM observation of the HMXB Vela X-1, conducted during the first cycle of the XRISM general observer programme and complemented by simultaneous XMM - Newton and NuSTAR coverage. This campaign targeted a critical orbital phase – when the neutron star is in inferior conjunction – during which significant changes in absorption are expected. Methods. We performed absorption-resolved spectral analyses during two time intervals of interest: the soft and hard hardness ratio (HR) intervals, as it is strongly correlated with absorption variability. Results. We observed a sudden transition in the HR from a soft to a hard state coinciding with an increase in the absorption column density. This is likely attributable to the onset of the accretion structure crossing our line of sight. With XRISM/Resolve, we also investigated the Fe K region, and we report for the first time the presence of a Fe K α doublet in the spectrum of Vela X-1 together with the presence of already known Fe K β and Ni K α lines that are produced in cold clumps embedded in the hot ionised wind. The measured line velocities of the order of 10 ² km s ⁻¹ are consistent with production sites in the vicinity of the neutron star. Conclusions. This precursor study with Vela X-1 shows the potential of XRISM to study in unprecedented detail the spectral evolution of wind-accreting X-ray binaries.