One of the distinctive properties of magnetars, young neutron stars powered mainly by magnetic energy, is the emission of short (≲1 s) bursts of hard X-rays. Such bursts have been observed in nearly all the known magnetars, although at different and time-variable rates of occurrence. In the past two decades, the INTEGRAL satellite has extensively covered the Galactic plane with good imaging capabilities, where most magnetars reside. We present the results of a comprehensive search for magnetar bursts in more than 20 yr of archival data of the INTEGRAL IBIS instrument (15 keV–1 MeV). This led to the detection of 1349 bursts with 30–150 keV fluence in the ∼2 × 10 ^−9 to 3 × 10 ^−6 erg cm ^−2 range from 21 of the 34 examined magnetars and candidate magnetars with well-known positions. The durations of the bursts, in terms of T _90 , follow a lognormal distribution centered at ∼0.1 s. Most of the detected bursts originated from three particularly active sources: 1E 1547–5408, SGR 1806–20, and SGR 1935+2154. The integral distributions of their burst fluences follow power laws with slopes β = 0.76±0.04, 0.95±0.06, and 0.92±0.10, respectively. The burst spectra are generally well fit with an exponentially cutoff power law with peak energy E _peak in the range ∼20−60 keV for SGR 1806–20 and SGR 1935+2154, while the bursts of 1E 1547–5408 are slightly harder ( E _peak ∼ 35−100 keV). A significant anticorrelation between E _peak and fluence is found for SGR 1806–20, which provided the largest number of bursts among the sources of our sample.

Magnetars are now known to be among the most strongly polarized celestial sources in X-rays. Here, we report on the 500 ks observation of the magnetar 1E 1547.0-5408 performed by the Imaging X-ray Polarimetry Explorer (IXPE) in 2025 March. The IXPE spectrum is well reproduced by a single thermal component with blackbody temperature kTBB similar to 0.67 keV and emission radius RBB similar to 1.2 km. The source exhibits a high linear polarization degree in the 2-6 keV band (PD = 47.7% +/- 2.9%) with polarization angle PA=75.degrees 8 +/- 1.degrees 8 , measured west of celestial north. While PA does not appear to vary with energy, there is some evidence (at the 1 sigma confidence level) of a minimum in PD between 3 and 4 keV, compatible with what is expected by partial mode conversion at the vacuum resonance in a magnetized atmosphere. Phase-resolved spectral and polarimetric analyses reveal that X-ray thermal radiation likely originates from a single, fairly small hot spot with a nonuniform temperature distribution. Fitting the phase-dependent PA measured by IXPE with a rotating vector model (RVM) constrains the source geometry and indicates that both the dipole axis and line-of-sight are misaligned with respect to the spin axis. Under these conditions, the high polarization of the source cannot be regarded as compelling evidence for the presence of vacuum birefringence in the star's magnetosphere. Nevertheless, the fact that the RVM successfully reproduces the modulation of the X-ray polarization angle and the behavior of PD with the energy hint once more at the presence of QED effects in magnetars.

We present the discovery of radio emission from the Be/X-ray binary A0538-66 with the Australian Square Kilometre Array Pathfinder, and results from a subsequent weekly monitoring campaign with the MeerKAT radio telescope. A0538-66, located in the Large Magellanic Cloud, hosts a neutron star with a short spin period (P approximate to 69ms) in a highly eccentric approximate to 16.6-d orbit . Its rare episodes of super-Eddington accretion, rapid optical and X-ray flares, and other peculiar properties make it an interesting system among high-mass X-ray binaries. Our MeerKAT data reveal that it is also one of the most radio-luminous neutron star X-ray binaries observed to date, reaching approximate to 3 & times;10(22)ergs(-1)Hz(-1)(at 1.28 GHz), with radio emission that appears to be orbitally modulated. We consider several possible mechanisms for the radio emission, and place A0538-66 in context by comparing it to similar systems.

Context. Very faint X-ray transients (VFXTs) are a class of X-ray binary systems that exhibit occasional outbursts with peak X-ray luminosities (LX ≲ 1036 erg s−1) much lower than those of typical X-ray transients. On 22 February 2024, during its daily Galactic center monitoring, Swift-XRT detected a VFXT 7 arcmin from Sgr A*, dubbing it Swift J174610–290018. Aims. We aim to characterize the outburst that occurred in 2024 and a second, distinct outburst in 2025 to understand the nature and accretion flow properties of this new VFXT. Methods. Swift-XRT light curves were used to constrain the duration of the two events. We carried out X-ray spectral analysis, exploiting XMM-Newton and NuSTAR data. We used Chandra and XMM-Newton observations from the last 25 years to constrain the quiescent luminosity of the source and to compare the two most recent outbursts with previous detections of the source. Results. During the 2024 outburst, which lasted about 50 days, the source reached a luminosity in the 2–10 keV band (L2–10) of ≃1.2 × 1035 erg s−1 (assuming it is located at the Galactic center, i.e., at a distance of 8.2 kpc). The 2025 outburst is shorter (about 5 days) and reached L2–10 ≃ 9 × 1034 erg s−1. The spectral features of the source include an excess at 6.5–7 keV, which can be associated either with a single reflection line or with the ionized Fe XXV and XXVI lines. The same source was identified in both the XMM-Newton and Chandra catalogs of point sources (known as 4XMM J174610.7–290020 and 2CXO J174610.7–290019). During previous detections the source displayed luminosity levels ranging from L2–10 ≃ 2 × 1032 to L2–10 ≃ 3 × 1033 erg s−1 between 2000 and 2010. Moreover, it exhibited a potential type I X-ray burst in 2004. Conclusions. The analysis of the outbursts and the potential type I burst strongly suggests that the VFXT Swift J174610–290018 is a neutron star low-mass X-ray binary. The source can be described as being an accretion disk corona source (as has been recently proposed by an XRISM/Xtend analysis). This scenario explains the overall low luminosity of this transient and the peculiar iron lines in the spectrum.

The term PeVatron designates astrophysical objects capable of accelerating particles to PeV energies (1 PeV = 10(15) eV). Their nature and particle acceleration mechanisms are uncertain, but ultra-high-energy gamma rays (>100 TeV) are produced when particles accelerated by either leptonic and hadronic PeVatrons interact with the surrounding medium or radiation fields. The atmospheric air shower observatory LHAASO detected photons with energies above 100 TeV from 43 sources in the Galactic Plane, proving the existence of PeVatrons within the Milky Way. In particular, one of the detections was a 1.4 PeV photon in spatial correspondence with Cygnus OB2, providing a strong hint that young massive stellar clusters (YMSCs) can act as PeVatrons. The next-generation ground-based Cherenkov telescopes will have unprecedented energy and angular resolution. Therefore, they will be able to resolve spatially YMSCs better than LHAASO. We focused on a sample of 5 YMSCs and their environments visible from either hemisphere with the CTAO or ASTRI Mini-Array. We modelled the secondary gamma-ray emission above 1 TeV and simulated observations of all sources. We devised methods for classifying YMSCs that could be detected as unidentified extended TeV sources and estimate the observational time needed to distinguish the morphology of different classes of sources. We study the morphology of the sources in our sample in order to identify their main features. We simulated observations of all sources with the instrument response function (IRF) of CTAO or ASTRI Mini-Array. We compare their emission distribution to the one of the TeV halos observed by HAWC. We parametrize their radial profiles in order to develop methodologies to classify them and to distinguish YMSCs from TeV halos based on their morphology. We expect some feature, such as the emission peak, to be key in differentiating between the two classes of objects. We then test them on a sample of sources of the first LHAASO catalogue.

Context. The candidate supernova remnant (SNR) G118.4+37.0 (Calvera's SNR), discovered as a faint radio ring at high Galactic latitude and coincident with extended Fermi/LAT gamma-ray emission, is likely associated with the X-ray pulsar 1RXS J141256.0+792204 (Calvera). Previous XMM-Newton data hinted at soft diffuse X-ray emission inside the ring, but lacked sufficient exposure for a detailed characterization. Aims. We aim to determine the distance, age, and physical conditions of Calvera's SNR and establish whether its gamma-ray emission is dominated by hadronic or leptonic processes. Methods. We obtained new XMM-Newton observations and produced count-rate images, along with equivalent width and median photon energy maps to identify optimal regions for spectral analysis. We complemented these observations with a reanalysis of Fermi/LAT gamma-ray data and new Telescopio Nazionale Galileo observations aimed at searching for H alpha emission. Results. The X-ray diffuse emission is well described by a model of shock-heated plasma with a temperature of kT similar to 0.15 keV, mildly under-solar N and O abundances, and densities n(e) =0.1-0.7 cm(-3). According to our estimates, Calvera's SNR is 10-20 kyr old and lies at a distance of 4-5 kpc. A distinct clump region shows harder emission equally well described by a thermal (kT similar to 1.7 keV) or a nonthermal model (Gamma similar to 2.7). The brightest X-ray area is close to the gamma-ray peak and an isolated H alpha filament. Conclusions. G118.4+37.0 is a middle-aged remnant which expands in a tenuous medium and encountered a denser phase, likely the relic of the wind activity of the massive progenitor star. The estimated SNR distance is consistent within the uncertainties with that estimated for Calvera, confirming that this peculiar pulsar was born in the explosion of a massive star high above the Galactic disk. Our measured ambient density, together with the patchy morphology of the gamma-ray emission and the detection of H alpha filaments indicate that a hadronic origin is compatible with the gamma-ray flux; although a mixed leptonic-hadronic scenario cannot be excluded.

We report the results on the short gamma-ray burst GRB 241107A, obtained with the IBIS instrument on board the INTEGRAL satellite. The burst had a duration of about 0.2 s, a fluence of 8 × 10 −7 erg cm −2 in the 20 keV–10 MeV range, and a hard spectrum, characterized by a peak energy of 680 keV. The position of GRB 241107A has been precisely determined because it fell inside the imaging field of view of the IBIS coded mask instrument. The presence of the nearby galaxy PGC 86046 in the 3′ radius error region suggests that GRB 241107A might be a giant flare from a magnetar rather than a canonical short gamma-ray burst. For the 4.1 Mpc distance of PGC 86046, the isotropic energy of 1.6 × 10 45 erg is in agreement with this hypothesis, which is also supported by the time-resolved spectral properties similar to those of the few other extragalactic magnetars giant flares detected so far.

We report on NICER X-ray observations of the Be X-ray binary A 0538-66 located in the Large Magellanic Cloud. Fast pulsations (69 ms) in this source were discovered in 1980 during a bright outburst in which it reached a luminosity of 8E38 erg/s, but were never reobserved since then. We clearly detected the pulsations at P=69.3055 +/- 0.0005 ms with a pulsed fraction of 20

Thanks to a recent observation with XMM-Newton, we discovered periodic pulsations at P = 9.6652 ± 0.0002 s in a new ultraluminous X-ray source (ULX) in the galaxy NGC 4631. This source, dubbed as X−8, shows one of the largest spin-up rates ever observed, P ̇ = ( − 9.6 ± 0.5 ) × 1 0 − 8 s s −1 . These findings indicate that the compact object is a neutron star, and X−8 is a new member of the pulsating ULX class. The 0.3–10 keV luminosity of X−8 is ∼3.4 × 10 39 erg s −1 , and its X-ray spectrum can be described by an absorbed disk blackbody or a cut-off power law, similar to what is observed in other pulsating ULXs. We discuss two possible causes for the large spin-up rate: Doppler shift from orbital motion of the neutron star and intrinsic spin-up due to accretion torque. This new ULX pulsar adds a key source to the small known population, and will enable future studies to better constrain the physical mechanisms responsible for their super-Eddington luminosities.

The most recent observational and theoretical results in the rapidly expanding field of high-energy gamma-ray astrophysics were discussed at the international conference “Gamma-2024” that took place in Milano in September 2024. This contribution summarises the 'rapporteur talk' relative to the Galactic science given at the end of the conference.

OGLE-2011-BLG-0462 is an isolated black hole of ∼7M⊙ at a distance of 1.5 kpc identified thanks to the astrometric microlensing technique. It is the first specimen discovered of the large population of ∼108 stellar-mass black holes that are believd to wander in the Galaxy. Electromagnetic radiation powered by accretion from the interstellar medium is expected from OGLE-2011-BLG-0462, but has not been detected at any wavelength. We present the results of a deep pointed observation with the Chandra satellite that provides an upper limit of 3× 1029 erg s−1 on the luminosity of OGLE-2011-BLG-0462 in the 0.5-7 keV energy range. This is about one order of magnitude below the previous limit obtained from shallower observations that serendipitously covered the sky position of this black hole. Our results are briefly compared with models of the source and with the X-ray upper limits for candidate isolated black holes and black holes in wide binary systems.

While Supernova Remnants (SNRs) are widely considered the primary accelerators of cosmic rays (CRs) up to hundreds of TeV, they struggle to account for the CR flux at PeV energies, suggesting the existence of additional PeVatrons. Observations from LHAASO (Large High Altitude Air Shower Observatory) have identified several PeVatron candidates, including some SNRs, pulsar wind nebulae, TeV halos and young massive star clusters (YMSCs). These objects accelerate particles that interact with the surrounding interstellar medium and radiation fields, producing very-high-energy gamma rays (>100 TeV), a key signature of both leptonic and hadronic PeVatrons. We simulate and model the emission of TeV halos and YMSCs, adopting radial emission profiles derived from observational data. Given the current angular resolution of gamma-ray instruments, these profiles often appear similar, making it challenging to distinguish between source classes. We explore how next-generation Imaging Atmospheric Cherenkov Telescopes (IACTs), namely the CTAO (Cherenkov Telescope Array Observatory) and the ASTRI Mini-Array (Astrofisica con Specchi a Tecnologia Replicante Italiana), can classify these sources based on their morphology. We test our classification methods, derived from the profile features of known sources, on simulated CTAO and ASTRI Mini-Array observations of unidentified extended sources from the first LHAASO catalog. We present the results of our analysis to highlight the potential of future IACT observations in identifying the nature of extended gamma-ray sources, refining PeVatron candidate classifications, and improving our understanding of cosmic-ray accelerators.

The Imaging X-ray Polarimetry Explorer (IXPE) observed for the first time highly polarized X-ray emission from the magnetar 1E 1841−045, targeted after a burst-active phase in 2024 August. To date, IXPE has observed four other magnetars during quiescent periods, highlighting substantially different polarization properties. 1E 1841−045 exhibits a high, energy-dependent polarization degree, which increases monotonically from ≈15% at 2–3 keV up to ≈55% at 5.5–8 keV, while the polarization angle, aligned with the celestial north, remains fairly constant. The broadband spectrum (2–79 keV) obtained by combining simultaneous IXPE and NuSTAR data is well modeled by a blackbody and two power-law components. The unabsorbed 2–8 keV flux (≈2 × 10 ^−11 erg cm ^−2 s ^−1 ) is about 10% higher than that obtained from archival XMM-Newton and NuSTAR observations. The polarization of the soft, thermal component does not exceed ≈25%, and may be produced by a condensed surface or a bombarded atmosphere. The intermediate power law is polarized at around 30%, consistent with predictions for resonant Compton scattering in the star magnetosphere; meanwhile, the hard power law exhibits a polarization degree exceeding 65%, pointing to a synchrotron/curvature origin.

We report on Neutron Star Interior Composition Explorer (NICER) X-ray observations of the Be X-ray binary A 0538–66 located in the Large Magellanic Cloud. Fast pulsations (69 ms) in this source were discovered in 1980 during a bright outburst in which it reached a luminosity of ∼8 × 10 ^38 erg s ^−1 but were never reobserved since then. We clearly detected the pulsations at P = 69.3055 ± 0.0005 ms with a pulsed fraction of ∼20% during a short time interval (∼11 minutes) on 2023 January 9, when A 0538–66 had a luminosity of ∼8 × 10 ^36 erg s ^−1 (0.3–10 keV). The pulsations were not detected in other NICER observations (total exposure ∼162.7 ks), during which A 0538–66 had a similar or lower luminosity. On 2023 February 8–9 the source exhibited a strong variability, with short flares reaching ∼10 ^38 erg s ^−1 , but no periodic pulsations were detected. Assuming the magnetospheric radius lies within the corotation radius during pulsations, we estimate the neutron star magnetic field is below ∼2.7 × 10 ^10 G. This would make A 0538–66 the high-mass X-ray binary with the weakest known magnetic field. We discuss implications for magnetic field evolution in accreting pulsars and propose that, alternatively, A 0538–66 has a stronger magnetic field, and during the NICER detection, a centrifugal barrier may have been active while part of the plasma accumulated at the magnetosphere sporadically leaked through it via an instability mechanism, allowing accretion onto the polar caps.

In recent years, the number of known sources emitting very- and ultra-high-energy gamma-rays has increased significantly thanks to facilities such as LHAASO and HAWC. Many of the observed sources are still unidentified or poorly constrained due to the limited angular resolution of these instruments; however, it is now ascertained that approximately half of them have a pulsar in coincidence. Some of these unidentified extended sources may be the result of the diffusion of leptons accelerated by the pulsar itself or in its nebula to energies exceeding 50 TeV. This new class of sources, called TeV halos, is characterized by a peculiar radial profile that, if properly resolved, is key to distinguishing them from other TeV sources that are associated with a pulsar, such as supernova remnants and pulsar wind nebulae. In this contribution, we consider all the pulsars which are spatially coincident with an unidentified extended TeV source, in order to quantify whether its spin-down power, age and distance allow the pulsar to produce a TeV halo with the observed flux and extension. We also investigate how the next generation of Imaging Atmospheric Cherenkov Telescopes (IACTs), namely the Cherenkov Telescope Array Observatory (CTAO) and the ASTRI Mini-Array, will observe and characterize these TeV halos. We present a set of simulated sources with the expected morphology and spectrum, and we show for which of them we can distinguish between TeV halos and other classes of extended sources.

In this new era of time-domain and multi-messenger astronomy, various new transients and new phenomena are constantly being discovered thanks to the rapid advances in observations, which provide the excellent opportunity to study the physics in the extreme environments. The enhanced X-ray Timing and Polarimetry mission (eXTP), planned to be launched in 2030, has several key advantages, including advanced polarimetry, high sensitivity large effective area, and wide energy range coverage, which make it a groundbreaking project in high-energy astrophysics. In this article, we briefly introduce the potential time-domain and multi-messenger targets for eXTP, including gravitational-wave (GW) counterparts, gamma-ray bursts (GRBs), magnetars and fast radio bursts (FRBs), tidal disruption events (TDEs), supernovae, high energy neutrinos and TeV active galactic nucleus (AGNs), and so on. We discuss the advantages of future eXTP observations for detecting these sources, their detection capabilities, the abilities to distinguish theoretical models, and their applications in gravity and cosmology.

For many years, it has been claimed that the Galactic ridge X-ray emission at the Galactic Center (GC) is truly diffuse in nature. However, with the advancement of modern X-ray satellites, it has been found that most of the diffuse emission is actually comprised of thousands of previously unresolved X-ray point sources. Further, many studies suggest that a vast majority of these X-ray point sources are magnetic cataclysmic variables (mCVs) and active binaries. One unambiguous way to identify these mCVs and other sources is by detecting their X-ray periodicity. Therefore, we systematically searched for periodic X-ray sources in the inner Galactic disk, including the GC region. We have used data from our ongoing XMM-Newton Heritage survey of the inner Galactic disk ($350^{\circ}\lesssim l\lesssim+7^{\circ}$ and $-1^{\circ}\lesssim b\lesssim +1^{\circ}$) plus the XMM-Newton archival observations of the GC. We computed the Lomb-Scargle periodogram of the light curves for the periodicity search. We fitted the energy spectra of the sources using a simple power-law model plus three Gaussians at 6.4, 6.7, and 6.9 keV for the iron $K$ emission complex. We detected periodicity in 26 sources. For 14 of them, this is the first discovery of periodicity. For the other 12 sources, we found periods similar to those already known, indicating no significant period evolution. We also searched for the Gaia counterparts of the periodic sources to estimate their distances using the Gaia parallax. We found a likely Gaia counterpart for seven sources. We have classified the sources into four categories based on the periodicity, hardness ratio, and the equivalent width of Fe $K$ line emission. Of the 14 sources where we detect the periodicity for the first time, four are likely to be intermediate polars, five are likely to be polars, two are neutron star X-ray binaries, and three are of unknown nature.

Recently, the Galactic magnetar SGR J1935+2154 has garnered attention due to its emission of an extremely luminous radio burst, reminiscent of fast radio bursts (FRBs). SGR J1935+2154 is one of the most active magnetars, displaying flaring events nearly every year, including outbursts as well as short and intermediate bursts. Here, we present our results on the properties of the persistent and bursting X-ray emission from SGR J1935+2154 during the initial weeks following its outburst on 2022 October 10. The source was observed with XMM-Newton and NuSTAR (quasi-)simultaneously during two epochs, separated by similar to 5 days. The persistent emission spectrum is well described by an absorbed blackbody plus power-law model up to an energy of similar to 25 keV. No significant changes were observed in the blackbody temperature (kT BB similar to 0.4 keV) and emitting radius (R BB similar to 1.9 km) between the two epochs. However, we observed a slight variation in the power-law parameters. Moreover, we detected X-ray pulsations in all the data sets and derived a spin-period derivative of P = 5.52 ( 5 ) x 10 - 11 s s-1. This is 3.8 times larger than the value measured after the first recorded outburst in 2014. Additionally, we performed quasi-simultaneous radio observations using three 25-32 m class radio telescopes for a total of 92.5 hr to search for FRB-like radio bursts and pulsed emission. However, our analysis did not reveal any radio bursts or periodic emission.

We report on the orbit of the binary system powering the most extreme ultraluminous X-ray pulsar known to date: NGC 5907 ULX-1 (hereafter ULX1). ULX1 has been the target of a substantial multi-instrument campaign, mainly in the X-ray band, but no clear counterparts are known in other bands. Although ULX1 is highly variable and pulsations can be transient (regardless of the source flux), the timing data collected so far allow us to investigate the orbit of this system. We find an orbital period P-orb = 5.7(-0.6)(+0.1) days and a projected semi-axis A(1) = 3.1(-0.9)(+0.8) lt-s . The most likely ephemeris is P-orb = 5.6585(6) days, A(1) = 3.1(4) lt-s, and the epoch of ascending nodes passage is T-asc = 57751.37(5) MJD. However, there are six similar solutions acceptable within 3 sigma. We find further indications that ULX1 is a high-mass X-ray binary. This implies that we are observing its orbit face on, with an inclination <5(degrees).