Pulse profiles provide a powerful diagnostic of the emission geometry and radiative processes in accreting X-ray pulsars, but their observed shape is affected by instrumental properties. We demonstrate that the energy-dependent pulsed fraction can be used as a robust timing cross-calibration diagnostic to combine XMM-Newton/EPIC-pn and NuSTAR observations. Using a simultaneous observation of...
X-ray binaries with red supergiant companions (RSGs) are extremely rare, and probe a very short-lived phase of binary evolution, just before the system is expected to undergo a second supernova. eRASS J085039.9-421151 (also Swift J0850.8-4219) was detected as a persistent source in the eROSITA survey at a relatively lower luminosity of 1e35 erg/s. The source was subsequently followed-up by...
Gamma-ray binaries are high-mass systems characterized by spectral energy distributions that peak near 100 MeV. X-ray observations of these systems reveal no detected spectral lines; only upper limits on Fe Kα are reported. This line deficit may be intrinsic, originating from extreme plasma ionization, or pulsar-driven disruption of the circumstellar environment. From an instrumental...
High Mass X-Ray binaries are fascinating systems. They consist of an O/B-type donor and a compact object (neutron star or black hole) embedded in the donor’s dense stellar wind, often in a close orbit, where orbital geometry and variability can be exploited to map the circumstellar environment.
During the years, we analysed interesting individual systems and, at the same time, developed some...
Ultraluminous X-ray sources (ULXs) represent the most extreme accreting X-ray binaries in the local Universe, with luminosities up to $ \sim10^{41}\ \rm erg/s$. They are now widely interpreted as stellar-mass compact objects accreting at super-Eddington rates in majority, as indicated by their soft X-ray spectral components, coherent pulsations in multiple systems, and the presence of...
NGC 5907 ULX-1, the most luminous ULX pulsar (peak luminosity 10⁴¹ erg/s), shows super-orbital modulation whose physical origin has implications for the magnetic field strength required to sustain super-Eddington accretion. From >10 years of Swift XRT monitoring (2014–2025), we characterise this modulation using Bayesian mixture models that properly marginalise over intermediate-flux states...
Quasi-periodic oscillations in the mHz range (mHz QPOs) have been detected in different X-ray binaries, hosting either a neutron star or a black hole. Nonetheless, the presence of mHz QPOs in a few ULXs was initially interpreted as the footprint of accreting intermediate-mass black holes. The detection of mHz QPOs first in M82 X-2, and then in M51 ULX-7 (two known pulsating ULXs), however, has...
Blazars exhibit strong variability across multiwavelength observations and multiple timescales. We present a systematic study of the X-ray spectral and timing variability of the TeV blazar PKS 2155-304 using Chandra and NuSTAR observations spanning 25 years (1999-2024). Timing analysis and flux distribution studies reveal moderate variability in most light curves and variable power spectral...
Ultraluminous X-ray sources (ULXs) are among the most luminous non-nuclear X-ray emitters in nearby galaxies, with luminosities exceeding the Eddington limit expected for stellar-mass black holes. They were historically considered promising candidates for hosting intermediate-mass black holes (IMBHs). However, the discovery of coherent pulsations in several ULXs, together with detailed...
X-ray pulsars (XRPs) provide a unique laboratory for studying accretion under extreme magnetic fields and strong-gravity conditions. Most are found in high-mass X-ray binaries, particularly systems with Be-star companions (BeXRBs), where episodic mass transfer can trigger bright X-ray outbursts reaching luminosities of ≳1E+38 erg/s. These systems probe the physics of magnetically channeled...
Nebular He II λ4686 in low-metallicity star-forming galaxies requires a hard ionizing spectrum beyond that produced by stellar populations. I present new deep Chandra and XMM-Newton observations that quantify the relative contributions of ULXs and hot diffuse plasma to this ionizing field in nearby metal-poor starbursts. Chandra’s sub-arcsecond imaging resolves individual ULXs, deconfuses them...
We present spatially resolved JWST NIRSpec and MIRI integral-field spectroscopy of the nebula surrounding the ultraluminous X-ray source Holmberg II X-1, providing the first direct view of high-ionization infrared emission on scales of only tens of parsecs in this system. By combining emission-line surface-brightness maps, diagnostic line ratios, and kinematic profiles, we detect intense [Ne...
Transitional millisecond pulsars (tMSPs) bridge the gap between accreting neutron stars in low-mass X-ray binaries and rotation-powered millisecond radio pulsars, offering a unique laboratory to study the interplay between accretion and pulsar activity. These systems display a subluminous X-ray state characterized by rapid transitions between high, low, and flaring emission...
A never-ending competition takes place around rapidly spinning, weakly magnetized neutron stars in low-mass X-ray binaries. Inflowing matter spirals inward and, during outburst, is channeled along the neutron star’s magnetic field lines onto its magnetic poles, producing coherent X-ray pulsations. As the accretion rate declines, the rotating magnetosphere pushes back, halting accretion and...
The Galactic center (GC) is home to the largest known concentration of exotic X-ray sources ever identified in our Galaxy, including compact objects like cataclysmic variables (CVs) and low-mass X-ray binaries (LMXBs), as well as thousands of faint X-ray sources whose nature is unclear. Recent studies indicate that the X-ray populations in the innermost region of our Galaxy vary over...
This study examines the observational signatures of optically thick winds in thermonuclear X-ray bursts (XRBs). By combining the wind models from Herrera et al. (2023) with the burst models from José et al. (2010), we reconstruct theoretical X-ray light-curves and effective temperature evolution. Using the HEASOFT package, we simulate observational counterparts of said theoretical predictions,...
We investigate the impact of thermonuclear X-ray bursts on the persistent emission of the low-mass X-ray binary 4U 1636–536. Archival observations from XMM-Newton and INTEGRAL were analyzed through time-resolved X-ray spectroscopy of a burst simultaneously detected by four instruments: EPIC-pn, RGS, JEM-X, and ISGRI. The persistent emission was modeled using a combination of accretion disk,...
We present a detailed temporal analysis of a Type I X-ray burst from the neutron star low-mass X-ray binary (NS-LMXB) XTE J1810−189, observed on 27 April 2023 with the Neutron Star Interior Composition Explorer (NICER). The burst displays a rapid rise time of 2.55 s, followed by an exponential decay with a timescale of 7.5 s, resulting in a total burst duration of ~13 s. Type I X-ray bursts...
In this contribution I will present recent results on the study of symbiotic stars, interacting systems in which a white dwarf accretes material from an evolved (typically a RGB or AGB) star. The very high luminosity and intrinsic variability of evolved stars complicates the identification and study of symbiotic stars. However, X-ray emission is a distinctive feature that opens a window to...
The mechanism for X-ray generation in the Gamma Cas analogues, a small group of highly variable Oe/Be stars, has been a mystery for several decades. They are characterised by their hard X-ray spectra, often including strong Fe fluorescence lines, and X-ray luminosities in the gap between those seen in similar stars and the more luminous Be/X-ray Binaries. They have also been observed to be...
V2487 Oph is a recurrent nova that underwent a fast and luminous eruption in 1998 (t₃ ≈ 8 days, peak magnitude 9.5). The host system hosts a massive white dwarf (~1.35 M☉) accreting from a donor star (~0.21 M☉) in a binary with an orbital period of 0.753 days (~18.1 hours). Previous X-ray observations conducted 2.7 and 3.2 years after the outburst suggested that accretion had resumed in the...
Accreting magnetic white dwarfs offer a unique window into accretion physics in binary systems. Like X-ray binaries, they harbour a standard Shakura-Sunyaev accretion disc whose inner edge can be magnetically truncated, yet their lower energies and longer dynamical timescales make the inner accretion geometry far more accessible. I will present results on DW Cnc, a well-studied intermediate...
The mass of a white dwarf (WD) is a fundamental parameter for understanding its formation, evolution, and role in binary systems. A large fraction of WDs are found in interacting binaries known as Cataclysmic Variables (CVs), where the WD accretes material from a low-mass donor star, typically a late-type main-sequence star. The X-ray emission from a class of magnetic CVs called the...
The identification of compact object type as either black hole (BH) or neutron star (NS) is fundamental to understanding their formation and evolution, and provides critical constraints concerning the final stages of supernovae. At the population level, X-ray binaries are linked to a number of host galaxy parameters, inform the expected rate of gravitational wave detections, and may have...
The newest edition of the XMM Slew Survey catalogue incorporates more than eight years of new observations, adding nearly 70,000 new detections of sources to the previous version. With an extended baseline now covering more than 20 years of observations the Slew catalogue presents an opportunity to detect bright, long-period, variable sources.
By cross-matching the sources in the XMM Slew...
Accreting compact objects are the primary X-ray populations in globular clusters. Their periodic variations spanning rotational spins and orbital motions, provide essential diagnostics for identifying progenitor populations and tracing evolutionary pathways. While recent surveys of Milky Way globular clusters have established a preliminary census of these sources, offering insights into...
Understanding the birthrate of magnetars, highly magnetized neutron stars, is essential for constraining their role in high-energy astrophysical phenomena such as gamma-ray bursts (GRBs) and fast radio bursts (FRBs). In this talk, we aim to estimate the magnetar birthrate in the Milky Way by analyzing the Galactic population of observed young neutron stars. In this sample, magnetars appear to...
The recently conducted eROSITA All-Sky Survey and the serendipitous source catalogues from pointed X-ray missions, like XMM-Newton, allow to significantly increase the population of thermally emitting isolated neutron stars (INSs). This promises exciting insights into the physics of ultra-dense matter, INS magnetic field evolution, and to study evolutionary pathways and links. However, with...
Magnetars, the most strongly magnetized class of the isolated neutron star population, are characterized by large-scale dipolar magnetic fields of order $10^{14}$ G, which are responsible for their rapid spin-down. The origin of such intense dipolar fields remains an open problem. In this talk, I will discuss the role of the chiral magnetic effect, arising from the chiral anomaly, which...
The spectacular Lighthouse nebula offers a rare opportunity to study how the most energetic pulsar wind particles escape into the ambient ISM near the apex of the bowshock of the highly supersonic pulsar. The >7-arcmin-long pulsar filament is by far the brightest among its peers and the only one allowing for informative spatially-resolved spectroscopy constraining the SED of the injected...
The simultaneous presence of kilohertz quasi-periodic oscillations (kHz QPOs) and relativistic Fe K emission lines in neutron star Low-Mass X-ray Binaries offers a unique opportunity to probe the innermost accretion flow. The frequency of a kHz QPO is thought to trace the orbital motion of matter in the inner accretion disk, while the Fe K line profile, shaped by relativistic broadening,...
GX 339–4 is a low-mass X-ray binary often used as an archetype, showing typical outburst behaviour. The source undergoes a full outburst every 2–3 years, passing through all known accretion states. We used NICER data to study the spectral-timing properties of the 2024 outburst of GX 339–4 and to compare them with the 2021 outburst. In particular we focused on rapid “flip-flop” transitions,...
The black hole candidate low-mass X-ray binary Swift J1727.8-1613 experienced one of the brightest outbursts ever observed in an X-ray binary in August 2023. Since then, this unique source has been observed across the entire electromagnetic spectrum. XMM-Newton monitored the low-mass X-ray binary for 3 days as it transitioned from the soft state – dominated by the multi-blackbody emission from...
NewAthena will advance our understanding of accretion onto stellar‑mass compact objects by enabling high‑throughput pointed X‑ray observations of low‑mass X‑ray binaries (LMXBs), including the elusive early stages of outbursts, through the combination of WFI wide‑field imaging/fast timing and X‑IFU high‑resolution spectroscopy. However, it is very difficult to predict when an LMXB will undergo...
The wealth and complexity of X-ray data provided by modern observatories has seen a dramatic improvement in recent years, in part due to new facilities like NICER and IXPE. This trend will accelerate further with new techniques like polarimetric timing, as well as future missions like NewAthena. On the other hand, the software modelling tools utilized by the community to model X-ray data are...
We are beginning to encounter computational and inference problems where complex models of atomic physics such as xillver must account for more and more parameters to properly model the absorption and emission lines present within our data. Coupled with the advent of XRISM, spectra tables must become unwieldingly large to compensate for the increase in energy resolution which makes it...
Neutron stars are excellent laboratories to study the physics of matter at extreme conditions, which are beyond the scope of any terrestrial experiments. Recent multimessenger observations of neutron stars such as the measurements of the tidal deformability from the gravitational wave observation, the simulataneous mass and radius measurements of several pulsars in X-rays by the...
X-ray eclipse mapping is a valuable modelling technique capable of constraining the mass and radius of compact objects in eclipsing binaries and probing the outflow from the companion star. In this talk, I will demonstrate the capabilities and recent developments of the X-ray Transit and EClipse software, X-TREC, through the modelling of the X-ray eclipses observed in three systems: the...
The Equation of State (EoS) of ultra-dense matter inside Neutron Stars (NS) is one of the long-standing questions of modern astrophysics and a key science goal of NewAthena. To constrain the composition of this dense matter, we measure the macroscopic observables of NSs, such as their masses and radii. The most precise method to measure the radius of NSs is Pulse Profile Modeling (PPM), where...
Neutron stars (NSs) in quiescent low-mass X-ray binaries (qLMXBs) have been used in the past two decades for mass and radius measurements to better constrain the equation-of-state of dense matter. However, various sources of systematic uncertainties were put forward, possibly biasing the radius values by as much as 50%. They include the unknown NS spin and atmospheric composition, as well as...
In this contribution, I will start with an overview of different types of equation of state modelling in the Bayesian formalism, to demonstrate the িmpact of different experimental and observational constraints. Further, I will present equations of state at finite temperature obtained with Brussels-Skyrme-on-a-Grid (BSkG) energy density functionals developed at Brussels, which are unified...
Neutron stars—pulsars—and their magnetospheres are key sources for multi-messenger astrophysics. Their emission spans the entire electromagnetic spectrum, they are strong candidates for contributing to the cosmic-ray positron excess, and theoretical models (though not yet confirmed observationally) suggest that they may also produce high-energy neutrinos in the TeV–PeV range. By combining...
The Magellanic Clouds (MCs) and local group dwarf spheroidal galaxies (dSphs) are invaluable laboratories for studying compact object populations and galactic evolution. While previous X-ray missions have provided foundational insights with instruments such as Chandra, XMM, and eROSITA, their sensitivity and spectral resolution have limited comprehensive population studies, especially at the...
