Pierre-Olivier Petrucci

Context. Swift J1727.8-1613 is an X-ray binary that was observed multiple times by IXPE , NICER , NuSTAR , and INTEGRAL during its 2023–2024 outburst. It was observed in a hard state at the beginning and the end of the outburst and in a soft state in between. Aims. We aim to reproduce the spectro-polarimetric signatures observed during two hard states: one bright at the beginning of the outburst and the other dim at the end. The two show similar X-ray polarimetric signatures, but their X-ray fluxes differ by two orders of magnitude. Methods. We modelled these hard state spectra in the JED–SAD framework, which combines a jet-emitting disk (JED) in the inner region of the accretion flow and a standard accretion disk (SAD) in the outer region. The X-ray polarisation properties of the best-fit JED–SAD configurations were then computed with the MONK general relativistic radiative transfer code. Results. The spectral characteristics of both the bright and dim hard states are well reproduced within the JED–SAD framework. Within our modelling, however, the dominant radiative process differs between the two states: self-Comptonised bremsstrahlung in the bright hard state and self-Comptonised synchrotron in the dim hard state. In the bright hard state, the resulting polarisation fraction remains below the observed value of ∼4%. Moreover, due to the JED’s large vertical optical depth (∼10), the polarisation angle is aligned with the accretion disk surface, i.e. there is a 90° difference with the observations. In contrast, the dim hard state’s simulated polarisation fraction is about 3% and the polarisation angle is perpendicular to the disk, both of which are broadly consistent with the IXPE measurements. Our simulations of the dim hard state are largely insensitive to the magnetic field configuration due to the strong depolarisation of the synchrotron seed photons by Faraday rotation. Conclusions. While the spectro-polarimetric properties of the dim hard state are well reproduced by our model, the bright hard state polarisation properties do not agree with the observations. We discuss different processes that could be responsible for the origin of the observed polarisation in the bright hard state: the presence of a non-thermal particle distribution, which would be consistent with the presence of a hard tail observed above 50 keV; and the electron scattering in an accretion-disk wind, which could modify both the polarisation fraction and angle. We discuss the limitations of the current JED–SAD framework and outline possible improvements to better reproduce the IXPE data.

Context . The X-ray emission of active galactic nuclei (AGNs) is commonly interpreted as arising from Comptonisation in a hot corona located above the accretion disc. In many sources, a prominent soft X-ray excess is also observed, often explained within the two-corona scenario, where a warm Comptonising layer produces the soft excess, while a hotter corona generates the hard X-ray continuum. However, the physical properties of these coronal components remain poorly constrained in very luminous quasars. Aims . We investigate the structure and physical properties of the X-ray-emitting coronae in two luminous radio-quiet quasars, PG 1407+265 ( z = 0.94) and RBS 229 ( z = 0.334), and test whether the two-corona scenario provides a consistent description of their broadband spectra. Methods . We performed a broadband spectral analysis combining XMM-Newton EPIC and Optical Monitor data with simultaneous NuSTAR observations and long-term Swift monitoring over months to years. The spectra were modelled using Comptonisation models to characterise the properties of both the warm and hot coronae. Results . Both quasars are X-ray-loud with respect to the standard α _OX – L _UV relation, with PG 1407+265 exhibiting the strongest deviation. Their broadband spectra are well reproduced by a two-corona configuration, consisting of a warm, optically thick Comptonising component that accounts for the soft excess and a hot corona responsible for the hard X-ray continuum. Both sources show high energy cut-offs in the range ∼70–80 keV. RBS 229 exhibits moderate reflection and a weak neutral Fe K α line, whereas no significant reflection features were detected in PG 1407+265. The soft excess is present in both quasars, but displays a markedly different behaviour for each: the warm-corona parameters in RBS 229 remain consistent across epochs, while PG 1407+265 displays strong variability, producing an extreme soft-excess episode extending up to ∼3 keV in the rest frame. Conclusions . These results provide new constraints on the properties of AGN coronae in the high-luminosity regime, which remains relatively poorly explored in observations. Both quasars show high energy cut-offs that are broadly consistent with the trends observed in terms of luminosity and accretion rates among AGN samples and safely below the runaway pair-production limit. No clear dependence of the warm-corona properties on the luminosity or the accretion rate was found, as both quasars show similar kT, τ , and soft-excess strengths despite their different regimes, with variations seen mainly in terms of the spectral slope and variability. The strong variability of the warm component in PG 1407+265, compared to the stability of RBS 229, supports a scenario in which the warm corona responds to accretion-flow changes, while remaining within a narrow range of physical conditions.

Detections of protoplanets are rare and protoplanetary disk features mischaracterized as planets are common. PDS 70 is one of only two stars known to host multiple confirmed protoplanets, PDS 70 b and c, and repeat detections of a third point-like source in the system suggest the presence of third inner planet. However, previous observations of this third source are insufficient to distinguish whether it is a planet or a concentrated dust clump in Keplerian motion. Our observations with VLTI/GRAVITY+ did not re-detect this point-like source, suggesting that it is, in fact, a dust clump and not a planet. These observations demonstrate how the angular resolving power of VLTI/GRAVITY+ can be used to distinguish between protoplanets and protoplanetary disk features.

We present the first X-ray polarimetric measurement of the neutron star low-mass X-ray binary system AX J1745.6−2901 conducted by the Imaging X-ray Polarimetry Explorer (IXPE) satellite. This transient source, located within ∼1 . ′ 5 of the Galactic center, was observed serendipitously during a MAXI J1744−294 observation with a duration of 150 ks. The complex nature of the region in which AX J1745.6−2901 is located poses a challenge for studying its polarization. By performing a detailed analysis of the contamination from MAXI J1744−294 and the Galactic center diffuse emission, we find the source polarization degree PD = 14.7% ± 4.0% and polarization angle PA = 122° ± 8°. The phase-resolved analysis shows increase in polarization during the eclipse phase, with PD = 34.2% ± 8.7%, suggesting that the polarization-inducing mechanisms are of scattering nature, probably originating from disk winds.

We report on the average and orbital phase-resolved polarization of Cyg X-3 in the hard state (HS) during the 2023 Imaging X-ray Polarimetry Explorer (IXPE) observational campaign. We find the polarization degree of 21.4% ± 0.4% and polarization angle of 92 . ° 2 ± 0 . ° 5 , compatible within 3 σ with the first HS IXPE observation in 2022. As the observed polarization depends on both the accretion geometry and the X-ray emission mechanism, and assuming it arises from reflection from the optically thick envelope surrounding the central source, our result indicates that both are similar in the two HS epochs on year-long timescales despite the source transitioning through an intermediate state in between. We discuss time- and energy-dependent polarization properties and their implications for the geometry and stability of the accretion funnel, finding significant orbital modulation of the polarization properties.

Context. NGC 1068 has long served as the reference Compton-thick Seyfert 2 galaxy. Decades of X-ray observations have established the presence of both neutral reflection and ionized circumnuclear emission. However, the limited spectral capabilities of previous CCD and grating data in the Fe–K band have prevented a clean separation of these components, thus leaving large uncertainties on key properties, such as the optical depth, structure, and kinematics of the reprocessing and emitting regions, and on their connection to nuclear outflows and feedback. Aims. We exploited high-resolution X-ray spectroscopy to disentangle the neutral and ionized iron emission in NGC 1068; constrained the physical properties of the cold reflector through line energies, widths, fluorescence ratios, and Compton-shoulder diagnostics; and investigated the origin, kinematics, and potential feedback role of the highly ionized Fe XXV and Fe XXVI emission. Methods. We analyzed an XRISM/Resolve observation of NGC 1068, focusing on the Fe K α and Fe K β fluorescent lines and on the Fe XXV and Fe XXVI emission complexes. Line centroid energies, intrinsic widths, flux ratios, and constraints on the Compton shoulder were derived through local spectral fitting, and compared with atomic calculations and theoretical predictions. Results. The centroid energies of the Fe K α and Fe K β lines tightly constrain the emitting material to be neutral or near neutral. The observed Fe K β /K α ratio, together with the stringent upper limit on the Compton shoulder (≲8−11% of the core flux), disfavor reflection dominated by a homogeneous classical Compton-thick medium, indicating that most of the neutral Fe K α emission arises in optically thin or moderately Compton-thick gas. The Fe XXV and Fe XXVI emission lines exhibit remarkably large velocity widths, of several thousand km s ⁻¹ . These broad profiles closely resemble the integrated optical and infrared [O III ] and [O IV ] lines associated with the large-scale biconical outflow, and are naturally interpreted as the X-ray signature of a more highly ionized, faster, and more spatially confined phase of the same outflow. Conclusions. The iron-K emission of NGC 1068 reveals a stratified circumnuclear environment in which neutral and highly ionized components arise in physically distinct regions. The neutral Fe K fluorescence originates predominantly in optically thin or mildly Compton-thick material, despite the persistently Compton-thick line-of-sight obscuration, indicating a geometrically complex cold reprocessor. The highly ionized iron emission lines trace a fast component consistent with a bipolar outflow on parsec scales, whose large velocities and inferred energetics suggest that it may represent an efficient channel for feedback. If similar ionized outflows and reflection geometries are common in heavily obscured Seyferts, they may constitute an underappreciated aspect of feedback and circumnuclear structure in this class of sources.

We present the X-ray analysis of coronal properties in a statistically representative sample of 23 mostly radio-quiet active galactic nuclei (AGN) from the SUpermassive Black holes Winds in X-rAYs campaign (SUBWAYS), focusing on quasars at redshifts 0.1<z<0.4 and bolometric luminosities 2 <L_ 44 bol ( erg/s)<2 . The main aim of this work is to investigate the properties of the hot corona through the study of the hard X-ray band emission, including a proper treatment of the soft X-ray band. High-quality X-ray spectra from 46 complemented by νstar data extending up to 30–40 keV in the rest frame, are available for this sample. The soft X-ray band (0.3–2 keV) spectrum is best fit by a warm corona model with a median temperature of sim0.40 keV, and an optical depth in the range τ consistent with previous results on lower-luminosity sources. The hard X-ray band is well described using a hot corona model, with a median high-energy cutoff of sim87 keV; 11 out of 23 of the sources have well constrained values at the lower end of the distribution of typical values found in Seyfert galaxies (sim100-200 keV). The derived median value of the optical depth (τ∼ 1-5) suggests the presence of a moderately optically thick corona. By combining the SUBWAYS results with literature samples at low and high redshifts, we assembled the largest sample to date of AGN with E_cut and accretion parameter measurements, finding a significant anticorrelation of E_cut with both λ_̊m Edd and łbol, with the median E_cut decreasing from sim250-300 keV at low accretion rates and luminosities to sim90-100 keV at high accretion rates and luminosities; this is consistent with increased coronal cooling, possibly driven by pair production. These results favor cooler, optically thicker coronae in luminous AGN compared to those in lower-luminosity Seyfert galaxies.

Context. The Galactic black hole candidate MAXI J1810−222 was recently reported to exhibit a notable absorption spectral feature at around 1 keV in low-resolution X-ray spectra from detectors resembling charge-coupled devices. The feature is typically correlated with the spectral state of the source being stronger in the soft states, as often occurs in the typical Fe K winds of X-ray binaries (XRBs). However, the results have hinted at rather extreme wind velocities of up to ∼0.1 c . Aims. We requested and obtained an observation with XMM-Newton to take advantage of the ten-fold higher spectral resolution ( R = λ /Δ λ ∼ 200 − 400) provided by the RGS detector to resolve the lines and break the degeneracy between different models and interpretations. Methods. We applied state-of-the-art models of plasma in photoionisation equilibrium and multi-phase interstellar medium (ISM). We performed further comparisons with a re-analysis of NICER and NuSTAR data. Results. The XMM-Newton /RGS spectrum is consistent with the presence of a mildly relativistic wind, confirming the earlier indications obtained with NICER; however, it places tighter constraints on the outflow properties, with the lines being intrinsically broad. The data would then favour magnetically driven winds, although thermal effects might still contribute to mass loading. NuSTAR and XMM-Newton (EPIC) show a further hotter component, indicating a stratified or multi-phase outflow. Fe K spectra taken with calorimetric detectors (e.g. Resolve on XRISM) will enable a high-resolution view of the complex extreme outflow in this source and shed new light on outflow processes in XRBs.

We present the first IXPE spectro-polarimetric observation of the black hole candidate MAXI J1744−294, a transient X-ray source observed during a bright 2025 outburst in the Galactic center region. The source has recently been identified as most likely a repeat outburst of the 2016 transient Swift J174540.2−290037. During the ∼150 ks observation, the source was detected in the soft state, and its spectrum was well described by an absorbed multicolor disk with a minor high-energy tail. We did not detect any significant polarization from the source, and hence we derived a 3 σ upper limit on the polarization degree of 1.3% in the 2–8 keV energy band. This result is consistent with previous findings for soft-state black hole binaries observed at low to intermediate inclination angles. By comparing the polarization degree upper limit with theoretical predictions for standard accretion disk emission, we constrain the disk inclination to i ≲ 38°–72°, depending on the black hole spin and the disk atmosphere albedo, consistent with inclination estimates obtained during the 2016 outburst of Swift J174540.2−290037.

The extended X-ray emission observed in the direction of several molecular clouds in the central molecular zone (CMZ) of our Galaxy exhibits spectral and temporal properties consistent with the X-ray echo scenario. This concept postulates that the observed signal is a light-travel-time delayed reflection of a short ( δt < 1.5 yr) and bright ( L _X > 10 ³⁹ erg s ⁻¹ ) flare that was most probably produced a few hundred years ago by Sgr A*. This scenario also predicts a distinct polarization signature for the reflected X-ray continuum, with the polarization vector being perpendicular to the direction toward the primary source and the polarization degree being determined by the scattering angle. We report the results of two deep observations of the currently brightest (in reflected emission) molecular complex Sgr A taken with the Imaging X-ray Polarimetry Explorer (IXPE) in 2022 and 2023. We confirm the previous polarization measurement for a large region encompassing the Sgr A complex with high significance. We also reveal an inconsistent polarization pattern for the brightest reflection region in its center. Specifically, the X-ray polarization from this region is almost perpendicular to the expected direction in the case of Sgr A* illumination, and it shows a smaller degree of polarization compared to the large region. Taken at face value, this could indicate the simultaneous propagation of several illumination fronts throughout the CMZ, with the origin of one of them not being Sgr A*. The primary source could be associated with the Arches stellar cluster or a currently unknown source located closer to the illuminated cloud, potentially lowering the required luminosity of the primary source. Although significantly deeper observations with IXPE would be required to unequivocally distinguish between the scenarios, a combination of high-resolution imaging and micro-calorimetric spectroscopy offers an additional promising path forward.