arXiv subjects

G. Ponti

Publications and source records attributed to G. Ponti.

At least 19 recordsLinked to original sources

arXiv2026

The SRG/eROSITA All-Sky Survey DR2: Cumulative X-ray catalogues from the first three surveys and multi-wavelength counterparts in the western Galactic hemisphere

The eROSITA telescope array on board the Spektrum-Roentgen-Gamma (SRG) mission began its all-sky survey program in December 2019, scanning the sky at an approximately six-month cadence. Here, we present new catalogues of point-like and extended X-ray sources derived from the first three completed eROSITA all-sky surveys (eRASS:3), covering the western Galactic hemisphere, which Germany's eROSITA consortium holds proprietary rights for. We describe the observational strategy, data processing, and analysis pipelines. We also characterise the resulting X-ray source populations. The eRASS:3 main catalogue contains nearly two million sources, including 1,911,744 point-like and 63,796 extended sources, detected in the 0.2-2.3 keV energy band, eROSITA's most sensitive energy window. This volume has doubled the X-ray source content of eRASS1 and provides a comprehensive census of X-ray-emitting objects across diverse astrophysical classes. We also released a secondary hard catalogue of nearly 15,000 sources detected in the harder 2.3-5.0 keV energy band. In addition, we released six catalogues, three for the main sample and three for the hard sample, in which we identify and classify the optical and infrared counterparts of eRASS:3 point-like sources. This approach delivers a homogeneous, high-quality identification of mostly extragalactic X-ray emitters; for example, we estimate that approximately 88% of the 1.4 million counterparts identified within the footprints of the Legacy Survey Imaging for DESI are extragalactic sources. This work has enabled the generation of samples optimised for completeness and purity, while expanding the discovery space for rare populations. The second data release (DR2) of the SRG/eROSITA all-sky survey is a catalogue-only release, comprising the catalogues presented in this work together with an updated version of the eROSITA upper flux limit server.

astro-ph.HE↗

arXiv2026

What's Missing in AGN Feedback? Lessons learnt from Magneticum, IllustrisTNG and Simba

Accurately balancing gas reservoirs, star formation, and feedback across cosmic time remains a central challenge for galaxy formation models in modern hydrodynamical simulations. While different feedback prescriptions reproduce selected local galaxy properties with varying success, the most pronounced discrepancies emerge in predictions for the hot gas content of dark matter halos. We examine three state-of-the-art cosmological simulations: Magneticum, IllustrisTNG, and SIMBA, which struggle to simultaneously reproduce observed galaxy and halo gas properties in the local Universe. We confront their predictions with spatially resolved galaxy data from MaNGA and recent constraints on the hot gas mass fraction-halo mass (fgas-Mh) relation from eROSITA and Sunyaev-Zel'dovich (SZ) measurements. Reproducing the observed fgas-Mh relation requires strong active galactic nucleus (AGN) feedback. However, such feedback often leads to excessive quenching in simulated galaxy populations. Magneticum and SIMBA match the observed gas fraction relation but predict an overabundance of quenched galaxies. In contrast, IllustrisTNG implements weaker AGN feedback, yielding more realistic star-forming fractions but systematically overpredicting hot gas masses in massive groups and poor clusters. Overall, these tensions indicate current feedback models remain incomplete, not only in the total energy injected but also in the timing, location, and coupling of this energy to the surrounding gas. Our results therefore highlight the need to revisit subgrid feedback prescriptions and develop more self-consistent models capable of simultaneously regulating galaxy growth and the thermodynamic properties of halo gas. Motivated by this discrepancy, a companion study will explore whether the feedback strengths required to match halo gas constraints inevitably lead to overquenching and distorted galaxy demographics.

astro-ph.GA↗

arXiv2026

Determination of the Solar System contribution to the soft X-ray sky

Solar wind charged particles interact with diffuse gas within the heliosphere, producing soft X-rays. This solar wind charge exchange (SWCX) process produces foreground emission that complicates interpretation of X-ray observations. In this work, we analyze X-ray observations of the western Galactic hemisphere by the Extended Roentgen Survey with an Imaging Telescope Array (eROSITA) instrument on the Spectrum-Roentgen-Gamma (SRG) spacecraft. These data avoid contamination by Earth's geocorona and are derived from four surveys of the full sky, including during the minimum of the Sun's activity cycle. We determine the SWCX contribution and subtract it from the survey, providing a less contaminated view of the diffuse soft X-ray sky. We also demonstrate that X-rays can be used to map the flow of interstellar matter through the Solar System.

astro-ph.SR↗

arXiv2026

Supermassive Black Hole Winds in X-rays: SUBWAYS IV. Tracing Radio Emission and Unveiling the Role of Winds

Most Active Galactic Nuclei (AGN) are Radio Quiet, with radio emission that may arise from star-formation activity, AGN-driven winds, weak jets, and coronal activity. Disentangling these mechanisms is challenging and requires detailed multi-wavelength investigation, but it is crucial for quantifying AGN feedback in galaxy evolution. We present a detailed radio investigation of 21 X-ray selected AGN in the Supermassive Black Hole Winds in X-Rays (SUBWAYS) sample (log Lbol = 44.9-46.3 erg/s, z=0.1-0.5), selected to systematically search for Ultra-Fast Outflows (UFOs). UFOs are detected in 30% of the targets, making the sample particularly well-suited for investigating the role and signatures of multi-scale outflows at different frequencies. We build the radio SED of the sources complementing our proprietary data, collected with the JVLA at 1.5 and 6 GHz, with images from LoTSS and other publicly available radio surveys between 150 and 1400 MHz. We investigate the role and occurrence of the aforementioned mechanisms, with particular interest in outflows and their possible relation with UFOs. We combined information on spectral indices, luminosities, and morphologies of the radio emission with properties derived in other wavebands, such as Star Formation Rate, X-ray luminosity, Eddington ratio or the UFO kinetic luminosity. All the sources are detected and are mostly consistent with RQ AGN. For 80% of the sources the data suggest the presence of an outflow (wind or weak jet). Interestingly, our results indicate that AGN with UFOs tend to have larger radio extension and a steep radio spectrum consistent with outflows. Moreover, the radio emission of the 6 UFO hosts is consistent with predictions from wind-driven shock models, possibly indicating a direct connection between the two phases. Alternatively, this may reflect physical conditions favouring the rise of both phenomena.

astro-ph.GA↗

arXiv2026

Even a precessing clock is right twice per orbit -- The super-periods of eRO-QPE2 and challenges for quasi-periodic eruption orbital models

We present O$-$C (``observed minus calculated'') timing analysis of the quasi-periodic eruption (QPE) source eRO-QPE2 with a multi-mission X-ray campaign, which includes 32 observed eruptions spanning a month (i.e. 325 QPE cycles). In relation to accretion (e.g. disk instability) models, the O-C is consistent with a damped random walk of the QPE recurrence, albeit with highly uncertain parameters. If instead an underlying orbital clock is present, eRO-QPE2 is consistent with a period of $P \sim 2.24$\,h and two hierarchical super-periodic modulations, with periods of $\sim 4.4$\,d ($\sim47$\,P) and $\approx 95$\,d ($\approx 1000$\,P). We found no negative period derivative, with $|\dot{P}| \lesssim 2 \times 10^{-6}$\,s/s at $3\sigma$. This disfavors high-eccentricity WDs and high-mass/eccentricity IMBHs via GW decay. For disk-collision models, where the $\dot{P}$ from gas drag and the QPE integrated energy provide bounds on the local disk density, a main-sequence star is disfavored as EMRI secondary unless stellar debris streams are present, while stripped stars remain allowed. The correlated odd/even O-C disfavors both disk crossings per orbit being observed. Interpreting the data with one \emph{observed} event per orbit, the short modulation is consistent with apsidal precession for $a \sim 140\,R_g$, $e \approx 0.1$, and $M_{\rm BH} \approx 1.5 \times 10^{5}\,M_\odot$. The longer modulation (much less constrained) is inconsistent with EMRI nodal precession and disk precession is allowed for a limited parameter volume, while there is a solution with a stable hierarchical triple system with an outer massive black hole at $\sim 0.4\,\mathrm{mpc}$ and mass $\sim(0.1-1) \times M_{\rm BH}$. However, no reliable solution can be found with more robust EMRI trajectory models, possibly due to narrow likelihood peaks in a multi-dimensional parameter space with sparse data.

astro-ph.HE↗

arXiv2026

Supermassive Black Hole Winds in X-rays: SUBWAYS V. Properties of hot coronae in quasars at intermediate redshift

We present the X-ray analysis of coronal properties in a statistically representative sample of 23 mostly radio-quiet AGN from the SUBWAYS campaign (SUpermassive Black holes Winds in XrAYs), focusing on quasars at redshifts $0.1 < z < 0.4 $ and bolometric luminosities $2 \times 10^{44} <L_{bol}(erg/s) < 2 \times 10^{46}$. 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 XMM-Newton, complemented by NuSTAR 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 fitted by a warm corona model with a median temperature of 0.40 keV, and an optical depth in the range $\tau$=20 - 40, 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 cut-off of 87 keV, at the lower end of the distribution of typical values found in Seyfert galaxies (100 - 200 keV). The derived median value of the optical depth ($\tau$ = 1 - 5) suggests the presence of a moderately optically thick corona. Combining the SUBWAYS results with literature samples at low and high redshift, we assemble the largest sample to date of AGN with E$_{cut}$ and accretion parameter measurements, finding a significant anticorrelation of E$_{cut}$ with both $\lambda_{Edd}$ and $L_{bol}$ with the median E$_{cut}$ decreasing from 250 - 300 keV at low accretion rates and luminosities to 90 - 100 keV at high accretion rates and luminosities - consistent with enhanced 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.

astro-ph.HE↗

arXiv2026

A XRISM view of the iron line complex in NGC 1068: Rethinking the prototypical Compton-thick AGN

We analyze a XRISM/Resolve observation of NGC1068, focusing on the Fe K$\alpha$ and Fe K$\beta$ 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 are derived through local spectral fitting, and compared with atomic calculations and theoretical predictions. The centroid energies of the Fe K$\alpha$ and Fe K$\beta$ lines tightly constrain the emitting material to be neutral or near-neutral. The observed Fe K$\beta$/K$\alpha$ ratio, together with the stringent upper limit on the Compton shoulder ($\lesssim$8--11% of the core flux), disfavour reflection dominated by a homogeneous, classical Compton-thick medium, indicating that most of the neutral Fe K$\alpha$ 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. The iron-K emission of NGC1068 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 warm bipolar outflow on parsec scales, whose large velocities and inferred energetics suggest that it may represent an efficient channel for feedback in a heavily obscured Seyfert galaxy.

astro-ph.HE↗

arXiv2026

Low-mass stars dominate the hot (0.7 keV) Galactic X-ray emission

The circumgalactic medium (CGM) of the Milky Way is composed of a tenuous atmosphere filled with multi-phase plasma, including a warm-hot virialised component. Recent studies suggest a much hotter (~0.7 keV) super-virial component detected in both absorption and emission. We want to shed light on the nature of this putative super-virial component. We analysed the X-ray background as observed by SRG/eROSITA over the entire western Galactic hemisphere. We show that low-mass stars provide a large fraction of the 0.7 keV emission. Indeed, a tight correlation is found between the surface brightness of the 0.7 keV emission and the mass distribution of the Milky Way across a large portion of the western Galactic hemisphere. The correlation coefficient implies an X-ray luminosity per unit of stellar mass comparable to that of the average low-mass stars within 10 pc of the Sun, suggesting that unresolved M dwarfs and F, G, and K type stars dominate the 0.7 keV emission. This emission is asymmetric with respect to the Galactic plane, influenced by the asymmetric distribution of nearby star-forming regions, and broadly consistent with the known offset of the Sun above the Galactic midplane. The remaining signal might be produced by the cumulative emission of stars of different types or ages, in addition to other sources (e.g. hot interstellar medium, Galactic corona, etc.). Assuming that the putative residual hot super-virial atmosphere is homogeneous and has a spherical beta profile with slope $\beta=0.4$, we constrain its density at 10 kpc to be $n_e<4\times10^{-4}$~cm$^{-3}$. Our findings may help refine models of the circumgalactic medium around external galaxies, advancing our understanding of hot baryon flows and galaxy evolution.

astro-ph.GA↗

arXiv2025

XRISM/Resolve reveals the complex iron structure of NGC 7213: Evidence for radial stratification between inner disk and broad-line region

We present the first high-resolution X-ray spectrum of NGC 7213 obtained with XRISM/Resolve, supported by simultaneous XMM-Newton, NuSTAR, and SOAR optical data. The XRISM spectrum resolves the neutral Fe\,K$\alpha$ into two components: a narrow core ($\rm FWHM = 650_{-220}^{+240}\,\rm km\,s^{-1}$) consistent with emission at the dust sublimation radius, and a broader, asymmetric line best described by disk-like emission from $\sim 100\,\rm R_{g}$. This disk component mirrors the profile of the double-peaked H$\alpha$ line observed in the optical. In addition, we detect broadened Fe XXV and Fe XXVI emission lines whose inferred locations bridge the gap between the inner disk and the optical broad-line region. The weak narrow Fe K$\alpha$ equivalent width ($\rm EW = 32 \pm 6\,eV$) and absence of a Compton hump imply a low-covering-fraction, Compton-thin torus. Together, these results reveal a radially stratified structure in NGC 7213, spanning nearly four orders of magnitude in radius, and place the source in an intermediate accretion state ($\rm \lambda_{Edd} = 0.001-0.01$) where the inner disk and BLR remain, while the torus shows signs of dissipation.

astro-ph.HE↗

arXiv2025

Investigating the mysterious nature of 1LHAASO J1740+0948u through deep XMM-Newton observations

1LHAASO J1740+0948u is a very-high-energy (VHE) source reported by LHAASO, with no counterpart at other wavelengths. It is located at 0.2{\deg} from PSR J1740+1000, a radio and gamma-ray pulsar placed well above the Galactic plane, which displays an X-ray tail. Despite the offset, the association between the two sources is likely. We aim to study the diffuse X-ray emission around PSR J1740+1000 and its tail to investigate the origin of 1LHAASO J1740+0948u through a multi-wavelength SED fitting, testing different scenarios. We analysed ~500 ks of XMM-Newton observations and studied for the first time the diffuse emission around the pulsar. We also analysed the tail and how its emission evolves as a function of distance. We then performed a fit of the SED, including the spectrum of 1LHAASO J1740+0948u and the X-ray data obtained from either the analysis of the tail or the diffuse emission, to understand whether one of the two X-ray sources could be related to the TeV emission and attempt a source classification. The diffuse X-ray emission analysis resulted in upper limits in the 0.5-10 keV range. The tail is best fitted with a power law with $\Gamma=1.76\pm0.06$ in 0.5-8 keV, with no significant detection of spectral variations with distance. We do not find a good SED fit that can explain both the X-ray tail and the LHAASO spectrum with reasonable parameters, suggesting that the TeV emission likely comes from an older X-ray-faint electron population. We then performed an SED fitting of the VHE spectrum combined with the upper limits on the diffuse emission, constraining the magnetic field to be as low as $B\leq1.2 \mu$G. We suggest that 1LHAASO J1740+0948u could represent either the relic PWN of PSR J1740+1000 or its pulsar halo. Our energy density results hint at a halo-like nature for 1LHAASO J1740+0948u, but deeper multi-wavelength observations are required to confirm this hypothesis.

astro-ph.HE↗

arXiv2025

Introducing The SHell misAlignment Detection for straylight Estimation (SHADE) algorithm: the case of XMM-Newton

When performing X-ray observations with a Wolter-I telescope, the presence of bright off-axis sources can introduce unfocused rays, known as straylight, which contaminate the detector and compromise the scientific analysis. Among the different components of straylight, single reflections off the hyperboloid section of the mirror shells often produce arc-like patterns on the detector. These arcs depend not only on the off-axis angle of the source but also on the geometrical alignment of the individual shells. In this paper, we introduce the SHell misAlignment Detection for straylight Estimation (SHADE) algorithm, a novel and flexible tool designed to infer the misalignment parameters of individual shells, reproduce the geometry of straylight arcs and predict its pattern on the detector. SHADE allows us to model each shell displacement with two parameters: $(\gamma,\xi)$ that represents the tilt amplitude and direction. While the algorithm is general and applicable to any Wolter-like telescope, we demonstrate its effectiveness using a set of XMM-Newton observations of the low-mass X-ray binary GX5-1. As a proof of concept, we recover the best-fit misalignment parameters for a selected shell, obtaining $\gamma = 21.9''^{+10.3}_{-9.02}$ and $\xi = 5.88^{+1.02}_{-0.97}$ rad. SHADE represents a new approach to diagnosing mirror misalignments from straylight patterns and can support both pre and post-launch calibration efforts and future telescope designs.

astro-ph.IM↗

arXiv2025

SRG/eROSITA No. 5: Discovery of quasi-periodic eruptions every ~3.7 days from a galaxy at z>0.1

Quasi-periodic eruptions (QPEs) are repeating soft X-ray bursts from the nuclei of galaxies, tantalizingly proposed to be extreme mass ratio inspirals. Here, we report the discovery of a new galaxy showing X-ray QPEs, the fifth found through a dedicated blind search in the \emph{SRG}/eROSITA all-sky survey data, hereafter named eRO-QPE5. Its QPE duration ($t_{\rm dur}\sim0.6$\,d), recurrence time ($t_{\rm recur}\sim3.7\,$d), integrated energy per eruption ($\sim3.4 \times 10^{47}\,$erg), and black hole mass ($M_{\rm BH}=2.9^{+5.4}_{-2.2}\times10^7\,M_{\astrosun}$) sit at the high end of the known population. Like other eROSITA or X-ray-discovered QPEs, no previous or concurrent optical-IR transient is found in archival photometric datasets, and the optical spectrum looks almost featureless. With a spectroscopic redshift of $0.1155$, eRO-QPE5 is the most distant QPE source discovered to date. Given the number of recent discoveries, we test for possible correlations and confirm a connection between $t_{\rm dur}$ and $t_{\rm recur}$, while we do not find any significant correlation involving either $M_{\rm BH}$ or the QPE temperature. The slope of the $t_{\rm dur}-t_{\rm recur}$ relation ($1.14\pm0.16$) is roughly consistent with predictions from star-disk collision models, with a preference for those that suggest that QPEs are powered by stellar debris streams around the orbiter. Considering this and previous discoveries, eROSITA has proved extremely successful in finding many QPE candidates given its grasp, namely its sensitivity and large field of view, and scanning capabilities over the full sky. We advocate the need of sensitive wide-area and time-domain oriented surveys from future-generation soft X-ray missions.

astro-ph.HE↗

arXiv2025

Disentangling the Galactic centre X-ray reflection signal using XMM-Newton data

We investigate the X-ray emission from the Galactic Centre (GC) region, focusing on the 6.4 keV fluorescent line of neutral or weakly ionised iron, which is commonly attributed to X-ray reflection from dense molecular clouds. Our goal is to separate the reflection signal from other physical X-ray components. We aim to produce a clean map of the 6.4 keV emission, thus providing a better understanding of the X-ray reflection processes in the GC. We utilised a deep mosaic of all available XMM-Newton observations, encompassing the central 40 square degrees of the Galaxy. The mosaics of two narrow bands centred at 6.7 keV and 6.4 keV, and a broader continuum band at lower energies (5-6.1 keV), provided valuable spatial and spectral information on the X-ray emission. These combined with the stellar mass distribution of our Galaxy enabled us to decompose the observed signal into physically meaningful components. Our analysis shows that the cleaned 6.4 keV band map, free from the contribution of bright and unresolved point sources, is predominantly shaped by X-ray reflection from dense molecular clouds. The spatial distribution of this emission, which strongly correlates with the molecular gas distribution in the Central Molecular Zone (CMZ), supports the interpretation that this map provides the best estimate of the X-ray reflection signal averaged over the last two decades. The cleaned reflection map produced could serve as a tool for future studies to quantify upper limits on the reflection contribution from low-energy cosmic rays in unilluminated regions. Moreover, we estimate that, on average within the CMZ, approximately 65% of the ridge emission contributes to the observed 6.4 keV emission, a factor that should be incorporated into upcoming investigations of the GC, such as polarisation studies of the reflected X-ray continuum from molecular clouds.

astro-ph.HE↗

arXiv2025

The eROSITA view on the halo mass-temperature relation: From low-mass groups to massive clusters

Galaxy groups and clusters are among the best probes of structure formation and growth in a cosmological context. Most of their baryonic component is dominated by the intracluster medium (ICM), whose thermodynamical properties serve as indicators of the halo's dynamical state and can be used for the halo mass determination in the self-similar scenario. However, baryonic processes, such as AGN feedback and gas cooling, may affect the global properties of the ICM, especially in the group regime. These effects might lead to deviations from self-similar predictions in galaxy groups' scaling relations, while they remain in place for massive galaxy clusters. Additionally, the low-mass end of the scaling relations, ranging from $10^{13}$ to $10^{14} M_\odot$, remains unclear and poorly populated, as current X-ray surveys detect only the brightest groups. Here, we present the Mass-Temperature relation across the full mass range, from massive clusters to low-mass groups ($10^{13}M_\odot$), as observed by eROSITA. Using spectral stacking from eROSITA eRASS1 data for optically selected galaxy groups, we find that, in the lower mass range, galaxy groups follow the power-law relation known for galaxy clusters. We further validate these results by conducting the same stacking procedure on mock eRASS:4 data using the Magneticum hydrodynamical simulation. This indicates that AGN feedback is more likely to affect the distribution of baryons in the intragroup medium rather than the overall halo gas temperature. No significant changes in the Mass-Temperature relation slope suggest that temperature can serve as a reliable mass proxy across the entire mass range. This validates the use of temperature-derived masses, particularly in cosmological studies, significantly broadening the mass range and enabling applications such as improving the cluster mass function studies and cosmological parameter estimate.

astro-ph.GA↗

arXiv2025

The impact of assembly history on the X-ray detectability of halos. From galaxy groups to galaxy clusters

Galaxy groups represent a significant fraction of the halo population, playing a crucial role in galaxy formation and evolution. However, their detection in X-rays remains challenging, raising questions about the physical mechanisms driving their detectability in current surveys. Using the Magneticum simulations, we construct a mock X-ray lightcone of the local Universe ($z<0.2$) to investigate the selection function of galaxy groups and clusters. We find that AGN activity is a key driver of baryon depletion, but late-time mergers boost X-ray brightness by replenishing the gas reservoir in the halos, highlighting the interplay between feedback processes and the environment. Our analysis shows that X-ray bright groups experience sustained late-time mass accretion, maintaining higher gas fractions and fueling the central supermassive black holes (SMBH), further increasing the X-ray emissivity in the core. In contrast, X-ray faint groups form earlier and lose most of their gas over time, resembling fossil groups. Magneticum predicts strong anti-correlations between gas fraction (or X-ray luminosity) and SMBH mass, stellar mass (both in the central galaxy and intracluster light), and group richness at fixed halo mass. We derive predictions on the hot gas fraction at fixed halos mass (e.g. a group of total mass $M_{500}=10^{13} M_{\odot}$ can have hot gas fractions in the range $f_\mathrm{gas}=0.02-0.06$ and a central SMBH with a median mass of $M_\mathrm{BH}=10^9 M_{\odot}$ and a scatter of $0.5$ dex) compatible with the most recent measurements of the baryonic fraction. These findings will aid the interpretation of future X-ray surveys, demonstrating the power of simulation-based inference.

astro-ph.GA↗

arXiv2025

25 years of XMM-Newton observations of the Sgr A complex: 3D distribution and internal structure of the clouds

Sgr A* is currently very faint. However, X-ray radiation reflected by the Sgr A complex, a group of nearby molecular clouds, suggests that it went through one or more periods of high activity some hundreds of years ago. We aim to determine whether previously proposed physical scenarios are consistent with the observed X-ray variability over the past 25 years, and to characterize the spatial distribution, shape, and internal structure of the clouds. We exploit the full set of XMM-Newton observations, extending the previously studied dataset on variability by at least 12 years. Starting from the recent IXPE result that places the so-called Bridge cloud 26 pc behind Sgr A*, we reconstruct the LOS position of the other clouds, assuming that they were illuminated by a single flare. Additionally, we derive the probability density function (PDF) of the molecular density. We also study the 3D geometry of the complex in case two flares illuminate the clouds. As of spring 2024, the lightfront is still illuminating the Sgr A complex, with the Bridge currently being the brightest cloud. The other clouds in the complex have faded significantly. In the single flare scenario, the Sgr A complex is located $\simeq$ 25 pc behind Sgr A*. In the past 25 years, the illuminated region spans 10-15 pc along the LOS. The derived PDF is roughly log-normal, consistent with previous Chandra results, with a possible high-density excess. Both a single and a multiple flares scenario can explain the observed X-ray variability. Previous concerns about the single flare scenario, raised by shorter monitoring, are now overcome in the 25 years of monitoring. If two flares illuminate the clouds, they must be separated by at least $\sim$ 30 years. We speculate that these clouds are closer to Sgr A* than the nuclear molecular ring at $\simeq$ 100-200 pc and possibly drifting from the ring to the inner region of the Galaxy.

astro-ph.GA↗

arXiv2025

State-dependent signatures of jets and winds in the optical and infrared spectrum of the black hole transient GX 339$-$4

GX 339$-$4 is one of the prototypical black hole X-ray transients, exhibiting recurrent outbursts that allow detailed studies of black hole accretion and ejection phenomena. In this work we present four epochs of optical and near-infrared spectroscopy obtained with X-shooter at the Very Large Telescope. The dataset includes two hard state spectra, collected during the 2013 and 2015 outbursts, and two soft state spectra observed during the 2021 outburst. Strong Balmer, Paschen, He I and He II emission lines are consistently observed in all spectra, while Brackett transitions and the Bowen blend are only prominent in the soft state. Although P-Cygni profiles are not identified, the presence of wind signatures, such as extended emission wings, flat-top and asymmetric red-skewed profiles, is consistently observed through most emission lines, suggesting the presence of wind-type ejecta. These features are particularly evident in the hard state, but they are also observed in the soft state, especially in the near-infrared. This strengthens the case for state-independent winds in black hole transients and increases the evidence for wind signatures in low-to-intermediate orbital inclination systems. We also study the spectral energy distribution, which provides evidence for the presence of synchrotron emission during the hard state. The jet significantly affects the near-infrared continuum, greatly diluting the emission features produced in the accretion flow. The simultaneous identification of both jet and wind signatures during the hard state reinforces the idea of a complex outflow scenario, in which different types of ejecta coexist.

astro-ph.HE↗

arXiv2024

New interpretation of the two hard X-ray sources IGR J17503-2636 and IGR J17507-2647

We report on the results of X-ray observations (XMM-Newton, INTEGRAL and Swift) of two hard X-ray sources, IGR J17503-2636 and IGR J17507-2647, whose nature is not fully elucidated in the literature. Three XMM-Newton observations covered the field of IGR J17503-2636, in 2020 and twice in 2023. The analysis of the two XMM-Newton observations performed in September 2023, six days apart, did not detect IGR J17503-2636, allowing us to pose the most stringent 3sigma upper limit on the source flux to date (~9.5x10^-14 erg/cm2/s, 2-10 keV, flux corrected for absorption). This value implies that the amplitude of the X-ray flux variability exceeds a factor of ~2100, compared with the discovery outburst in 2018. A candidate X-ray periodicity at 0.335397(3) seconds has been barely detected (significance of about 3.8sigma) from IGR J17503-2636 with XMM-Newton (pulsed fraction of (10+/-1) per cent). The new data, put into the context of previous literature, allow us to propose a new classification of IGR J17503-2636 as a symbiotic X-ray binary, rather than a candidate supergiant fast X-ray transient. IGR J17507-2647 was formerly reported below 10 keV only during Chandra observations performed in 2009. We report here on two XMM-Newton observations that serendipitously covered the source field in 2020 and in 2023, finding a stable X-ray emission, both in X-ray flux and spectral shape. The long-term, persistent X-ray emission has also been probed by several Swift/XRT short observations and by INTEGRAL data spanning several years. We have detected an iron line in the emission (with centroid energy in the range of 6.3-6.6 keV), never reported before in the IGR J17507-2647 spectrum. The source properties favor the identification with a cataclysmic variable.

astro-ph.HE↗