Search

We report on the broadband spectral and timing properties of the accreting millisecond X-ray pulsar IGR J17498−2921 during its April 2023 outburst. We used data from NICER (1–10 keV), NuSTAR (3–79 keV), Insight-HXMT (2–150 keV), and INTEGRAL (30–150 keV). We detected significant 401 Hz pulsations across the 0.5–150 keV band. The pulse fraction increases from ∼2% at 1 keV to ∼13% at 66 keV. We detected five type-I X-ray bursts, including three photospheric radius expansion bursts, with a rise time of ∼2 s and an exponential decay time of ∼5 s. The recurrence time is ∼9.1 h, which can be explained by unstable thermonuclear burning of hydrogen-deficient material on the neutron star surface. The quasi-simultaneous 1–150 keV broadband spectra from NICER, NuSTAR and INTEGRAL can be aptly fitted by an absorbed reflection model, relxillCp, and a Gaussian line of instrumental origin. The Comptonized emission from the hot corona is characterized by a photon index Γ of ∼1.8 and an electron temperature kTe of ∼40 keV. We obtained a low inclination angle i ∼ 34°. The accretion disk shows properties of strong ionization, log(ξ/erg cm s−1)∼4.5, over-solar abundance, AFe ∼ 7.7, and high density, log(ne/cm−3)∼19.5. However, a lower disk density with normal abundance and ionization could also be possible. Based on the inner disk radius of Rin = 1.67RISCO and the long-term spin-down rate of −3.1(2)×10−15 Hz s−1, we were able to constrain the magnetic field of IGR J17498−2921 to the range of (0.9 − 2.4)×108 G. [ABSTRACT FROM AUTHOR]

Context. The Spektrum-Roentgen-Gamma (SRG)/extended Roentgen Survey with an Imaging Telescope Array (eROSITA) All-Sky Survey (eRASS) is expected to contain ∼100 quasars that emitted their light when the universe was less than a billion years old, that is, at z > 5.6. By selection, these quasars populate the bright end of the active galactic nuclei (AGN) X-ray luminosity function, and their space density offers a powerful demographic diagnostic of the parent super-massive black hole (SMBH) population. Aims. Of the ⪆400 quasars that have been discovered at z > 5.6 to date, less than 15% have been X-ray detected. We present a pilot survey to uncover the elusive X-ray luminous end of the distant quasar population. Methods. We have designed a quasar selection pipeline based on optical, infrared and X-ray imaging data from DES DR2, VHS DR5, CatWISE2020 and the eRASS (up to its four-pass cumulative version, eRASS:4). The core selection method relies on SED template fitting. We performed optical follow-up spectroscopy with the Magellan/LDSS3 instrument for the redshift confirmation of a subset of candidates. We have further obtained a deeper X-ray image of one of our candidates with Chandra ACIS-S. Results. We report the discovery of five new quasars in the redshift range 5.6 < z < 6.1. Two of these quasars are detected in eRASS and are, therefore, X-ray ultra-luminous by selection. We also report the detection of these quasars at radio frequencies. The first one is a broad absorption line quasar, which shows significant, order-of-magnitude X-ray dimming over 3.5 years, corresponding to six months in the quasar rest frame. The second X-ray detected quasar is a jetted source with compact morphology. We show that a blazar configuration is likely for this source, making it one of the most distant blazars known to date. Conclusions. With our pilot study, we demonstrate the power of eROSITA as a discovery machine for luminous quasars in the epoch of reionization. The X-ray emission of the two eROSITA detected quasars are likely to be driven by different high-energetic emission mechanisms, a diversity which we will further explore in a future systematic full-hemisphere survey. [ABSTRACT FROM AUTHOR]

Galaxy groups contain the majority of bound mass with a significant portion of baryons due to the combination of halo mass and abundance (Cui 2024). Hence they serve as a crucial missing piece in the puzzle of galaxy formation and the evolution of large-scale structures in the Universe. In observations, mass-complete group catalogues are normally derived from galaxy redshift surveys detected through various three-dimensional group-finding algorithms. Confirming the reality of such groups, particularly in the X-rays, is critical for ensuring robust studies of galaxy evolution in these environments. Recent works have reported numerous optical groups that are X-ray undetected (see, e.g. Popesso et al. 2024), sparking debates regarding the reasons for the unexpectedly low hot gas fraction in galaxy groups. To address this issue, we utilize zoomed-in simulations of galaxy groups from the novel Hyenas project to explore the range of hot gas fractions within galaxy groups and investigate the intrinsic factors behind the observed variability in X-ray emission. We find that the halo formation time can play a critical role–we see that groups in haloes that formed earlier exhibit up to an order of magnitude brighter X-ray luminosities compared to those formed later. This suggests that undetected X-ray groups are preferentially late-formed haloes and highlights the connection between gas fraction and halo formation time in galaxy groups. Accounting for these biases in galaxy group identification is essential for advancing our understanding of galaxy formation and achieving precision in cosmological studies. [ABSTRACT FROM AUTHOR]

Context. Inferring spectral parameters from X-ray data is one of the cornerstones of high-energy astrophysics, and is achieved using software stacks that have been developed over the last 20 years and more. However, as models get more complex and spectra are obtained with higher resolutions, these established software solutions become more feature-heavy, difficult to maintain and less efficient. Aims. We present jaxspec, a Python package for performing this task quickly and robustly in a fully Bayesian framework. Based on the JAX ecosystem, jaxspec allows the generation of differentiable likelihood functions compilable on core or graphical process units (GPUs), enabling the use of robust algorithms for Bayesian inference. Methods. We demonstrate the effectiveness of jaxspec samplers, in particular the no U-turn sampler, using a composite model and comparing what we obtain with the existing frameworks. We also demonstrate its ability to process high-resolution spectroscopy data using original methods by reproducing the results of the Hitomi collaboration on the Perseus cluster, while solving the inference problem using variational inference on a GPU. Results. We obtain identical results when compared to other software and approaches, meaning that jaxspec provides reliable results while being ~10 times faster than existing alternatives. In addition, we show that variational inference can produce convincing results even on high-resolution data in less than 10 minutes on a GPU. Conclusions. With this package, we aim to pursue the goal of opening up X-ray spectroscopy to the existing ecosystem of machine learning and Bayesian inference, enabling researchers to apply new methods to solve increasingly complex problems in the best possible way. Our long-term ambition is the scientific exploitation of the data from the newAthena X-ray Integral Field Unit (X-IFU). [ABSTRACT FROM AUTHOR]

Context. Extragalactic fast X-ray transients (FXTs) are short-duration (∼ks) X-ray flashes of unknown origin, potentially arising from binary neutron star (BNS) mergers, tidal disruption events, or supernova shock breakouts. Aims. In the context of the BNS scenario, we investigate the possible link between FXTs and the afterglows of off-axis merger-induced gamma-ray bursts (GRBs). Methods. By modelling well-sampled broadband afterglows of 13 merger-induced GRBs, we make predictions for their X-ray light curve behaviour had they been observed off-axis, considering both a uniform jet with core angle θC and a Gaussian-structured jet whose edge lies at an angle θW = 2θC. We compare their peak X-ray luminosity, duration, and temporal indices α (where F ∝ tα) with those of the currently known extragalactic FXTs. Results. Our analysis reveals that a slightly off-axis observing angle of θobs ≈ (2.2 − 3)θC and a structured jet are required to explain the shallow (|α|≲0.3) temporal indices of the FXT light curves, which cannot be reproduced in the uniform-jet case at any viewing angle. In the case of a structured jet with truncation angle θW = 2θC, the distributions of the duration of the FXTs are consistent with those of the off-axis afterglows for the same range of observing angles, θobs ≈ (2.2 − 3)θC. While the distributions of the off-axis peak X-ray luminosity are consistent only for θobs = 2.2θC, focussing on individual events with different intrinsic luminosities reveals that the match of all three properties (peak X-ray luminosity, duration and temporal indices) of the FXTs at the same viewing angle is possible in the range θobs ∼ (2.2 − 2.6)θC. Despite the small sample of GRBs analysed, these results show that there is a region of the parameter space – although quite limited – where the observational properties of off-axis GRB afterglow can be consistent with those of the newly discovered FXTs. Future observations of FXTs discovered by the recently launched Einstein Probe mission and GRB population studies combined with more complex afterglow models will shed light on this possible GRB-FXT connection, and eventually unveil the progenitors of some FXTs. [ABSTRACT FROM AUTHOR]

Reprocessed X-ray radiation from active galactic nuclei (AGN) carries important information about the properties of the circumnuclear material around the black hole. The X-ray photons travel from the very centre of the system and interact with that material often producing strong emission lines. The |$\rm {Fe\, K\alpha }$| Compton shoulder (CS) is formed by fluorescent |$\rm {Fe\, K\alpha }$| photons that perform Compton scatterings with the intercepting material and lose energy to form the distinct shoulder shape. In this work, we use the ray-tracing code RefleX to explore how the physical properties of the medium, as well as its geometry, affect the shape of the CS. We start by running simulations using a simple toroidal reflector, to test the effect of the metal composition, metallicity, column density, dust presence and velocity on the |$\rm {Fe\, K\alpha }$| line, and its CS. We confirm that the shape of the CS is sensitive to the optical depth of the intercepting medium, which can be regulated by either changing the metal composition or the line-of-sight column density of the circumnuclear material. Next, we create a series of models, which feature different geometrical configurations of dust and gas, and explore how the CS is affected by such configurations finding that components that can regulate the line-of-sight column density affect the |$\rm {Fe\, K\alpha }$| and its CS. Finally, we test whether observatories such as the recently launched XRISM and future Athena will make the CS a useful spectral feature of nearby AGN, by applying specific models on simulated spectra of the Circinus galaxy. The CS has the potential to be used to help constrain properties of the circumnuclear material yet with some limitations. [ABSTRACT FROM AUTHOR]

Dead time is a common instrumental effect of X-ray detectors, which would alter the behaviour of timing properties of astronomical signals, such as distorting the shape of power density spectra (PDS), affecting the root-mean-square of potential quasi-periodic oscillation signals, etc. We revisit the effects of the dead time of Medium Energy X-ray telescope (ME) onboard Insight - HXMT based on the simulation of electronic read-out mechanism that causes the dead time and the real data. We investigate dead time effects on the pulse profile as well as the quasi–periodic oscillation (QPO) signals. The dead time coefficient suggests a linear correlation with the observed count rate in each phase bin of the pulse profile according to the simulation of periodic signal as well as the real data observed on Swift J0243.6+6124. The Fourier-amplitude-difference (FAD) method could well recover the intrinsic shape of the observed PDS in the case that the PDS is from two identical detectors. We apply this technique on ME, by splitting the nine FPGA modules into two groups. The results indicate that the FAD technique suits the case when two groups of detectors are not largely different; and the recovered PDS of Sco X-1 observed by ME slightly enhances the significance of the previously known QPO signal, meanwhile the root-mean-square of QPO is significantly improved. We provide the FAD correction tool implemented in HXMTDAS for users in the future to better analyse QPO signals. [ABSTRACT FROM AUTHOR]

Pulsars (PSRs) and Pulsar Wind Nebulae (PWNe) form some of the most interesting high-energy astrophysical systems. Their prominent synchrotron emission makes them ideal candidates for polarimetry. Here, after briefly summarizing the scientific rationale underpinning the importance of their polarimetric studies, we review the current status and achievements obtained by the IXPE mission. For the first time, we have space- and phase-resolved X-ray data that allow us to set constraints on the geometry and level of turbulence of the magnetic field which, in turn, can help us to better understand which acceleration and radiation model(s) might be at work in these systems. Interestingly, PWNe show a large variety in terms of polarization degree that might indicate key physical differences, still to be further investigated. [ABSTRACT FROM AUTHOR]

We report on new multifrequency Very Large Array (VLA) radio observations and Chandra X-ray observations of a radio-loud quasar with a ∼300 kpc-long jet, PKS 1127−145, during a flaring event detected in γ-rays by the Fermi Large Area Telescope in December 2020. The high angular resolution of the new radio images allows us to disentangle for the first time the kiloparsec-scale inner jet from the core contribution. The inner radio jet, up to 15 kpc from the core, is highly polarized (33 percent) and the magnetic field is parallel to the jet axis. At about 18 arcsecs from the core, the jet slightly bends and we observe a re-brightening of the radio emission and a 90-degree rotation of the magnetic field, likely highlighting the presence of a shock that is compressing the magnetic field to a plane perpendicular to the jet axis, where efficient particle acceleration takes place. At the same position, the X-ray emission fades, suggesting a deceleration of the bulk velocity of the jet after the bend. A change in velocity and collimation of the jet is supported by the widening of the jet profile and the detection of a limb-brightened structure connecting the bending region with the jet termination. The limb-brightened structure might indicate the coexistence of both longitudinal and transverse velocity gradients at the jet bending. There is no evidence of significant brightening of the kiloparsec-scale jet in the radio or X-ray band during the γ-ray flare. The X-ray flux, F2 − 10 keV = (6.24 ± 0.57)×10−12 ergs s−1 cm−2, measured by Chandra from the quasar core is consistent with the flux measured by the X-ray Telescope on board the Neil Gehrels Swift Observatory after the high-energy flare. Our results indicate that the γ-ray flaring region is located within the VLA source core. [ABSTRACT FROM AUTHOR]

We present an updated catalog of sources detected by the Mikhail Pavlinsky ART-XC telescope aboard the Spektrum-Roentgen-Gamma (SRG) observatory during its all-sky survey. It is based on the data of the first four and the partially completed fifth scans of the sky (ARTSS1-5). The catalog comprises 1545 sources detected in the 4–12 keV energy band. The achieved sensitivity ranges between ~4 × 10−12 erg s−1 cm−2 near the ecliptic plane and ~7 × 10−13 erg s−1 cm−2 near the ecliptic poles, which is a ~30–50% improvement over the previous version of the catalog based on the first two all-sky scans (ARTSS12). There are ~130 objects, excluding the expected contribution of spurious detections, that were not known as X-ray sources before the SRG/ART-XC all-sky survey. We provide information, partly based on our ongoing follow-up optical spectroscopy program, on the identification and classification of the majority of the ARTSS1-5 sources (1463), of which 173 are tentative at the moment. The majority of the classified objects (964) are extragalactic, a small fraction (30) are located in the Local Group of galaxies, and 469 are Galactic. The dominant classes of objects in the catalog are active galactic nuclei (911) and cataclysmic variables (192). [ABSTRACT FROM AUTHOR]

Context. Over recent decades, astronomy has entered the era of massive data and real-time surveys. This is improving the study of transient objects – although they still contain some of the most poorly understood phenomena in astrophysics, as it is inherently more difficult to obtain data to constrain the proposed models. Aims. In order to help detect these objects in their brightest state and build synergies with multi-wavelength real-time surveys, we have built a quasi-real time automatic transient detection system for the XMM-Newton pipeline: the Search for Transient Objects in New detections using Known Sources (STONKS) pipeline. Methods. STONKS detects long-term X-ray transient events by automatically comparing new XMM-Newton detections to any available archival X-ray data at this position, sending out an alert if the variability between observations (defined as the ratio between the maximum flux and the minimum flux or upper limit) is over 5. This required an initial careful cross-correlation and flux calibration of various X-ray catalogs from different observatories (XMM-Newton, Chandra, Swift, ROSAT, and eROSITA). A Bayesian framework was put into place to solve any ambiguous associations. We also systematically computed the XMM-Newton upper limits at the position of any X-ray source covered by the XMM-Newton observational footprint, even without any XMM-Newton counterpart. The behavior of STONKS was then tested on all 483 observations performed with imaging mode in 2021. Results. Over the 2021 testing run, STONKS provided a daily alert rate of 0.7−0.5+0.7 alerts per day, about 80% of them corresponding to serendipitous sources. Among the detected variable serendipitous sources, there are: several highly variable active galactic nuclei (AGNs) and flaring stars, as well as new X-ray binary and ultra-luminous X-ray source candidates, some of which are present here. STONKS also detected targeted tidal disruption events, ensuring its ability to detect other serendipitous events. As a byproduct of our method, the archival multi-instrument catalog contains about one million X-ray sources, with 15% of them involving several catalogs and 60% of them having XMM-Newton (pointed or slew) upper limits. Conclusions. STONKS demonstrates a great potential for revealing future serendipitous transient X-ray sources, providing the community with the ability to follow-up on these objects a few days after their detection with the goal of obtaining a better understanding of their nature. The underlying multi-instrument archival X-ray catalog will be made available to the community and kept up to date with future X-ray data releases. [ABSTRACT FROM AUTHOR]

Although flux variability is one of the defining properties of accretion flows on to supermassive black holes, its dependence on physical parameters such as the mass of the compact object and the Eddington ratio remains under discussion. In this paper, we address this issue using the structure function statistic to measure the variability at X-ray wavelengths of a sample of optically selected QSOs with available black hole masses and Eddington ratios. We present a new Bayesian methodology for estimating the structure function tailored to the Poisson nature of the X-ray data. This is applied to 15 548 SDSS DRQ16 QSOs with repeat observations in the XMM – Newton archive and/or the SRG/eROSITA All Sky Survey. The X-ray structure function monotonically increases to time intervals of about 10–15 yrs, consistent with scenarios in which instabilities of the accretion disc contribute to the X-ray variability on long time-scales. Additionally, there is evidence that the amplitude of the stochastic X-ray flux variations rises with decreasing black hole mass and Eddington ratio. This finding imposes stringent constraints on empirical models of Active Galactic Nuclei variability derived from local samples, emphasizing the significance of high-redshift population studies for comprehending the stochastic flux variations in active black holes. [ABSTRACT FROM AUTHOR]

Our study focuses on characterizing the highly ionized gas within the Milky Way's (MW) Circumgalactic Medium (CGM) that gives rise to ionic transitions in the X-ray band 2–25 Å. Utilizing stacked Chandra /ACIS-S MEG and LETG spectra toward Quasar (QSO) sightlines, we employ the self-consistent hybrid ionization code phase to model our data. The stacked spectra are optimally described by three distinct gas phase components: warm [log (T /K) ∼ 5.5], warm-hot [log (T /K) ∼6], and hot [log (T /K) ∼ 7.5] components. These findings confirm the presence of the hot component in the MW's CGM indicating its coexistence with warm and warm-hot gas phases. We find this hot component to be homogeneous in temperature but inhomogeneous in column density. The gas in the hot component requires overabundances relative to solar to be consistent with the Dispersion Measure (DM) from the Galactic halo reported in the literature. For the hot phase we estimated a DM =  |$55.1^{+29.9}_{-23.7}$|  pc cm−3. We conclude that this phase is either enriched in Oxygen, Silicon, and Sulfur, or has metallicity over 6 times solar value, or a combination of both. We do not detect Fe L-shell absorption lines, implying O/Fe ≥ 4. The non-solar abundance ratios found in the supervirial gas component in the Galactic halo suggest that this phase arises from Galactic feedback. [ABSTRACT FROM AUTHOR]

We present a series of numerical models suitable for X-ray polarimetry of accreting systems. First, we provide a spectropolarimetric routine that integrates reflection from inner optically thick walls of a geometrical torus of arbitrary size viewed under general inclination. In the studied example, the equatorial torus is illuminated by a central isotropic source of X-ray power-law emission, representing a hot corona. Nearly neutral reprocessing inside the walls is precomputed by Monte Carlo code stokes that incorporates both line and continuum processes, including multiple scatterings and absorption. We created a new xspec model, called xsstokes , which in this version enables efficient X-ray polarimetric fitting of the torus parameters, observer's inclination and primary emission properties, interpolating for arbitrary state of primary polarization. Comparison of the results to a Monte Carlo simulation allowing partial transparency shows that the no-transparency condition may induce different polarization by tens of per cent. Allowing partial transparency leads to lower/higher polarization fraction, if the resulting polarization orientation is perpendicular/parallel to the rotation axis. We provide another version of xsstokes that is suitable for approximating nearly neutral reflection from a distant optically thick disc of small geometrical thickness. It assumes local illumination averaged for a selected range of incident angles, representing a toy model of a diffuse corona of various physical extent. Assessing both xsstokes variants, we conclude that the resulting polarization can be tens of per cent and perpendicularly/parallelly oriented towards the rotation axis, if the reflecting medium is rather vertically/equatorially distributed with respect to a compact central source. [ABSTRACT FROM AUTHOR]

Measurements of neutron star mass and radius or tidal deformability deliver unique insight into the equation of state (EOS) of cold dense matter. EOS inference is very often done using generalized parametric or non-parametric models, which deliver no information on composition. In this paper, we consider a microscopic nuclear EOS model based on a field theoretical approach. We show that current measurements from NICER and gravitational wave observations constrain primarily the symmetric nuclear matter EOS. We then explore what could be delivered by measurements of mass and radius at the level anticipated for future large-area X-ray timing telescopes. These should be able to place very strong limits on the symmetric nuclear matter EOS, in addition to constraining the nuclear symmetry energy that determines the proton fraction inside the neutron star. [ABSTRACT FROM AUTHOR]

To identify progenitors and investigate evidence of He burning, we searched for decay radiation of freshly synthesized 44Ti in four young nearby thermonuclear supernova remnants: Kepler, SN 1885, G1.9+0.3, and SN 1006, by analysing the up-to-date NuSTAR archival data. No apparent flux excess from the 68 and 78 keV line emissions accompanying decay was detected above the power-law continuum applied for the remnants and the absorbed stray light. By comparing the inferred upper limits of the line flux and the initial 44Ti masses with a wide variety of supernova nucleosynthesis models, we placed constraints on the supernova progenitors. We derived the first NuSTAR line flux upper limit for Kepler and ruled out most of the double-detonation scenarios with a thick He layer under low density. We estimated, for the first time, the upper limit for SN 1885, which is high because of the large distance, yet still remains consistent with the He shell detonation. The new flux and mass limit of G1.9+0.3 derived from a longer total exposure is lower than the results from previous studies and evidently excludes explosive burning of He-rich matter. The relatively advanced age and the large spatial extent of SN 1006 have prevented meaningful constraints. [ABSTRACT FROM AUTHOR]

The indirect search for dark matter is typically restricted to individual photon bands and instruments. In the context of multiwavelength observations, finding a weak signal in large foreground and background at only one wavelength band is hampered by systematic uncertainties dominating the signal strength. Dark matter particle annihilation is producing Standard Model particles of which the prompt photon emission is searched for in many studies. However, also the secondary emission of charged particles from dark matter annihilation in the TeV range results in comparable or even stronger fluxes in the GHz–GeV range. In this study, we calculate the prompt and secondary emission of a scotogenic weakly interacting massive particle (WIMP) with a mass of 1 TeV in 27 dwarf galaxies of the Milky Way. For the secondary emission, we include inverse Compton scattering, bremsstrahlung, and synchrotron radiation, which results in a 'triple hump' structure characteristic for only dark matter and no other astrophysical source. In order to determine the best candidates for multi-instrument analyses, we estimate the diffuse emission component of the Milky Way itself, including its own dark matter halo from the same scotogenic WIMP model. We find signal-to-background ratios of individual sources on the order of 10−3 to 10−2 across X-ray to γ-ray assuming J factors for the cold dark matter distribution inferred from observations and no additional boosting due to small-scale clumping. We argue that a joint multiwavelength analysis of all nearby galaxies and the extension towards the cosmic gamma-ray background is required to disentangle possible dark matter signals from astrophysical background and foreground. [ABSTRACT FROM AUTHOR]

Electron density profiles obtained from radio occultation experiments reveal significant ionization occurring at altitudes below 120 km in the Venusian ionosphere. The presence of such ionization remains unexplained when considering only major neutrals and the resulting ion chemistry. In this study, we investigate the role of minor neutrals, including NO, O2, C, Ar, H2, and H, in the lower altitudes of the Venusian ionosphere using a one-dimensional photochemical model and Akatsuki radio science measurements. We derive the density of minor neutrals from the profiles of major neutrals. Our analysis demonstrates that NO+ and O |$_2^+$| ions exhibit a notable presence below 140 km. When we incorporate the minor neutrals, electron density increases below 115 km but remains unchanged above this altitude. Specifically, the density of NO+ increases below 125 km, with corresponding reductions in O |$_2^+$|⁠. The increase in NO+ above 115 km can be attributed to the charge-exchange reaction between O |$_2^+$| and NO. However, below 115 km, the photoionization of NO results in a net increase in NO+ and electron density. These findings highlight the significant role played by minor neutrals, particularly below 115 km, in shaping the Venusian ionosphere at low altitudes. [ABSTRACT FROM AUTHOR]

Extragalactic fast X-ray transients (FXTs) are a class of soft (0.3–10 keV) X-ray transients lasting a few hundred seconds to several hours. Several progenitor mechanisms have been suggested to produce FXTs, including supernova shock breakouts, binary neutron star mergers, or tidal disruptions involving an intermediate-mass black hole and a white dwarf. We present detailed host studies, including spectroscopic observations of the host galaxies of seven XMM-Newton -discovered FXTs. The candidate hosts lie at redshifts 0.0928 < z < 0.645 implying peak X-ray luminosities of 1043 erg s−1< LX < 1045 erg s−1 and physical offsets of 1 kpc < r proj < 22 kpc. These observations increase the number of FXTs with a spectroscopic redshift measurement by a factor of 2, although we note that one event is re-identified as a Galactic flare star. We infer host star formation rates and stellar masses by fitting the combined spectroscopic and archival photometric data. We also report on a contemporaneous optical counterpart search to the FXTs in Pan-STARRS and ATLAS by performing forced photometry at the position of the FXTs. We do not find any counterpart in our search. Given our constraints, including peak X-ray luminosities, optical limits, and host properties, we find that XRT 110 621 is consistent with an supernova shock breakout (SN SBO) event. Spectroscopic redshifts of likely host galaxies for four events imply peak X-ray luminosities that are too high to be consistent with SN SBOs, but we are unable to discard either the binary neutron star or white dwarf–intermediate-mass black hole tidal disruption event scenarios for these FXTs. [ABSTRACT FROM AUTHOR]

The circum-galactic medium (CGM) can feasibly be mapped by multiwavelength surveys covering broad swaths of the sky. With multiple large data sets becoming available in the near future, we develop a likelihood-free Deep Learning technique using convolutional neural networks (CNNs) to infer broad-scale physical properties of a galaxy's CGM and its halo mass for the first time. Using CAMELS (Cosmology and Astrophysics with MachinE Learning Simulations) data, including IllustrisTNG, SIMBA, and Astrid models, we train CNNs on Soft X-ray and 21-cm (H  i) radio two-dimensional maps to trace hot and cool gas, respectively, around galaxies, groups, and clusters. Our CNNs offer the unique ability to train and test on 'multifield' data sets comprised of both H  i and X-ray maps, providing complementary information about physical CGM properties and improved inferences. Applying eRASS:4 survey limits shows that X-ray is not powerful enough to infer individual haloes with masses log (M halo/M⊙) < 12.5. The multifield improves the inference for all halo masses. Generally, the CNN trained and tested on Astrid (SIMBA) can most (least) accurately infer CGM properties. Cross-simulation analysis – training on one galaxy formation model and testing on another – highlights the challenges of developing CNNs trained on a single model to marginalize over astrophysical uncertainties and perform robust inferences on real data. The next crucial step in improving the resulting inferences on the physical properties of CGM depends on our ability to interpret these deep-learning models. [ABSTRACT FROM AUTHOR]

We report the discovery of a faint radio filament near PSR J0538+2817 in the NVSS, CGPS, and the Rapid ASKAP Continuum Survey data. This pulsar is plausibly associated with the supernova that gave rise to the Spaghetti nebula (Simeis 147). The structure is one-sided and appears to be almost aligned (within 17 degrees) with the direction of the pulsar's proper motion, but in contrast to the known cases of pulsar radio tails, it is located ahead of the pulsar. At the same time, this direction is also approximately (within 5 degrees) perpendicular to the axis of the extended non-thermal X-ray emission around the pulsar. No X-ray or optical emission is detected from the filament region, although the end point of the radio filament appears to be adjacent to a filament of Hα emission. We speculate that this structure might represent a filament connecting pulsar wind nebula (PWN) with the ambient interstellar medium filled with relativistic electrons escaping the pulsar nebula, i.e. a radio analogue of X-ray filaments of Guitar and Lighthouse PWNs and filaments of non-thermal radio emission in the Galactic Centre. [ABSTRACT FROM AUTHOR]

The eROSITA telescope array aboard the Spektrum Roentgen Gamma (SRG) satellite began surveying the sky in December 2019, with the aim of producing all-sky X-ray source lists and sky maps of an unprecedented depth. Here we present catalogues of both point-like and extended sources using the data acquired in the first six months of survey operations (eRASS1; completed June 2020) over the half sky whose proprietary data rights lie with the German eROSITA Consortium. We describe the observation process, the data analysis pipelines, and the characteristics of the X-ray sources. With nearly 930 000 entries detected in the most sensitive 0.2–2.3 keV energy range, the eRASS1 main catalogue presented here increases the number of known X-ray sources in the published literature by more than 60%, and provides a comprehensive inventory of all classes of X-ray celestial objects, covering a wide range of physical processes. A smaller catalogue of 5466 sources detected in the less sensitive but harder 2.3–5 keV band is the result of the first true imaging survey of the entire sky above 2 keV. We present methods to identify and flag potential spurious sources in the catalogues, which we applied for this work, and we tested and validated the astrometric accuracy via cross-comparison with other X-ray and multi-wavelength catalogues. We show that the number counts of X-ray sources in eRASSl are consistent with those derived over narrower fields by past X-ray surveys of a similar depth, and we explore the number counts variation as a function of the location in the sky. Adopting a uniform all-sky flux limit (at 50% completeness) of F05–2 keV > 5 × 10−14 erg s−1 cm−2, we estimate that the eROSITA all-sky survey resolves into individual sources about 20% of the cosmic X-ray background in the 1–2 keV range. The catalogues presented here form part of the first data release (DR1) of the SRG/eROSITA all-sky survey. Beyond the X-ray catalogues, DR1 contains all detected and calibrated event files, source products (light curves and spectra), and all-sky maps. Illustrative examples of these are provided. [ABSTRACT FROM AUTHOR]

Context. The soft X-ray instrument eROSITA on board the Spectrum-Roentgen-Gamma (SRG) observatory has successfully completed four of the eight planned all-sky surveys, detecting almost one million X-ray sources during the first survey (eRASS1). The catalog of this survey will be released as part of the first eROSITA data release (DR1). Aims. Based on X-ray aperture photometry, we provide flux upper limits for eRASS1 in several energy bands. We cover galactic longitudes between 180° ≲ l ≲ 360° (eROSITA-DE). These data are crucial for studying the X-ray properties of variable and transient objects, as well as non-detected sources in the eROSITA all-sky survey data. Methods. We performed aperture photometry on every pixel of the SRG/eROSITA standard pipeline data products for all available sky tiles in the single detection band (0.2–2.3 keV). Simultaneously, we performed the same analysis in the three-band detection at soft (0.2–0.6 keV), medium (0.6–2.3 keV), and hard (2.3–5.0 keV) energy bands. Based on the combination of products for the individual bands, we are also able to provide aperture photometry products and flux upper limits for the 0.2–5.0 keV energy band. The upper limits were calculated based on a Bayesian approach that utilizes detected counts and background within the circular aperture. Results. The final data products consist of tables with the aperture photometry products (detected counts, background counts, and exposure time), a close-neighbor flag, and the upper flux limit based on an absorbed power-law spectral model (Γ = 2.0, NH = 3 × 1020 cm−2). The upper limits are calculated using the one-sided 3σ confidence interval (CL) of a normal distribution, representing CL = 99.87%. The aperture photometry products allow for an easy computation of upper limits at any other confidence interval and spectral model. These data are stored in a database with hierarchical indexes in order to offer a fast query option. Conclusions. We provide a detailed description of the process of retrieving SRG/eROSITA upper limits for a large set of input positions, as well as of the eROSITA data, the X-ray aperture photometry, the upper limit calculation, and the final data products. The eROSITA upper flux limits represent either the maximum flux of potential non-detections or the 3σ upper flux uncertainty of detected sources. We emphasize the importance of choosing the right spectral model that ought to match the spectral shape of the source of interest: the wrong spectral model can produce discrepancies of up to 30% in the final flux upper limit value. We also describe the architecture of the database and the web tool, which are designed to handle large queries on input positions. [ABSTRACT FROM AUTHOR]

Context. S 308 is an X-ray emitting bubble that surrounds the Wolf–Rayet star WR6. The structure shines in the optical as well and is thus known as the Dolphin Nebula. Due to its large angular extent, it has been covered at only 90% with past XMM-Newton observations. Aims. Thanks to the unique dataset provided by the all-sky survey performed in X-rays by SRG/eROSITA, we can show for the first time the image of the bubble in its entire extent in this band, together with its spectral characterization. Moreover, we have tried to apply the same procedure for other wind-blown bubbles detected in the optical/IR and we searched for X-ray extended emission around them. Methods. We first analyzed the diffuse emission of S308, providing a detailed spectral analysis. We then considered a sample of 22 optical/IR selected wind-blown bubbles from a previous study based on WISE data, providing an estimate of the X-ray flux for the first time. Results. We obtained the best fit for S308 with a two-temperature non-equilibrium plasma model (kT1 = 0.8-0.3+0.8 keV and kT2 = 2-1+3 keV) showing super-solar N abundance and low absorption. We did not detect any of the 22 optical/IR emitting bubbles in X-rays, but using our best fit model, we estimated the 3σ flux upper limits for each bubble. Conclusions. We demonstrate the new possibility offered by SRG/eROSITA to study known wind-blown bubbles and look for other ones. A two-temperature plasma description seems to fit the data quite well for S308. Since all of the 22 bubbles studied still remain undetected by SRG/eROSITA, it is very likely that absorption effects and spatial compactness are responsible for the challenges standing in the way of detecting these bubbles in soft X-rays. [ABSTRACT FROM AUTHOR]

The recent serendipitous discovery of a new population of short duration X-ray transients, thought to be associated with collisions of compact objects or stellar explosions in distant galaxies, has motivated efforts to build up statistical samples by mining X-ray telescope archives. Most searches to date, however, do not fully exploit recent developments in the signal and imaging processing research domains to optimize searches for short X-ray flashes. This paper addresses this issue by presenting a new source detection pipeline, STATiX (Space and Time Algorithm for Transients in X-rays), which directly operates on three-dimensional X-ray data cubes consisting of two spatial and one temporal dimension. The algorithm leverages wavelet transforms and the principles of sparsity to denoise X-ray observations and then detect source candidates on the denoised data cubes. The light curves of the detected sources are then characterized using the Bayesian blocks algorithm to identify flaring periods. We describe the implementation of STATiX in the case of XMM–Newton data, present extensive validation and performance verification tests based on simulations and also apply the pipeline to a small subset of seven XMM–Newton observations, which are known to contain transients sources. In addition to known flares in the selected fields, we report a previously unknown short duration transient found by our algorithm that is likely associated with a flaring Galactic star. This discovery demonstrates the potential of applying STATiX to the full XMM–Newton archive. [ABSTRACT FROM AUTHOR]

We present a broad analysis of X-ray polarimetric observational prospects for radio-quiet active galactic nuclei (AGN), focusing on the role of parsec-scale components. We provide a revision of self-consistent type-1 and type-2 generic AGN radiative transfer models that were obtained with a Monte Carlo code stokes , evaluating the effects of absorption and scattering. Our model consists of a central disc–corona emission obtained with the kynstokes code in the lamp-post geometry, an equatorial wedge-shaped dusty torus and two symmetric conical polar outflows. We argue that the information on the mutual orientation, shape, relative size, and composition of such components, usually obtained from spectroscopy or polarimetry in other wavelengths, is essential for the X-ray polarization analysis of the obscured type-2 AGNs. We provide general detectability prospects for AGNs with 2–8 keV polarimeters onboard of the currently flying Imaging X-ray Polarimetry Explorer (IXPE) satellite and the forthcoming enhanced X-ray Timing and Polarimetry mission. Finally, we assess the role of contemporary X-ray polarimetry in our understandings of the unified AGN model after the first year and a half of IXPE operation. [ABSTRACT FROM AUTHOR]

Most active galactic nuclei (AGNs) in the local Universe are obscured. In these obscured AGNs, an excess is usually observed in the soft X-rays below ∼2 keV above the absorbed X-ray continuum. This spectral component is associated with the scattering of X-ray photons off free electrons in the narrow-line region (NLR), and/or to photoionized lines. Recent studies have found that in highly obscured AGNs this component has lower flux relative to the primary X-ray continuum than in less obscured AGNs. This is measured by the scattering fraction, or f scatt, which is the ratio of the scattered flux to the continuum. Here, we use the ray-tracing platform reflex to perform simulations of scattered X-ray radiation to test two possible explanations for this phenomenon: (1) sources with lower f scatt are viewed at higher inclinations or (2) low f scatt sources are characterized by larger covering factors. We consider a conical NLR of free electrons, while allowing the column density and opening angle (and hence covering factor) to vary. We also consider electron densities inferred from observations, and from simulations carried out with the spectral synthesis code cloudy. Our simulations show f scatt is expected to be related to both the inclination angle and covering factor of the torus; however, the observed negative correlation between f scatt and N H can only be explained by a positive relation between the column density and the covering factor of the obscuring material. Additional contributions to f scatt can come from unresolved photoionized lines and ionized outflowing gas. [ABSTRACT FROM AUTHOR]

Pulsars (PSRs) and Pulsar Wind Nebulae (PWNe) form some of the most interesting high-energy astrophysical systems. Their prominent synchrotron emission makes them ideal candidates for polarimetry. Here, after briefly summarizing the scientific rationale underpinning the importance of their polarimetric studies, we review the current status and achievements obtained by the IXPE mission. For the first time, we have space- and phase-resolved X-ray data that allow us to set constraints on the geometry and level of turbulence of the magnetic field which, in turn, can help us to better understand which acceleration and radiation model(s) might be at work in these systems. Interestingly, PWNe show a large variety in terms of polarization degree that might indicate key physical differences, still to be further investigated.

The role of energetic outflows from galactic nuclei in shaping galaxy formation and evolution is still shrouded in uncertainty. In this study, we shed light on this complex phenomenon by presenting evidence for a large-scale bipolar radio/X-ray-emitting bubble-like structure emanating from the central region of the nearby disc galaxy M106 (NGC 4258). Our findings, based on Low-Frequency Array survey data and Chandra observations, provide a glimpse into the underlying physical processes driving this enigmatic structure. Similar to the eROSITA / Fermi bubbles in our own Galaxy, the M106 bubbles enclose diffuse hot plasma and are partially bounded by prominent radio/X-ray-emitting edges. We constrain the magnetic field and cosmic-ray properties of the structure. The analysis of the X-ray data gives an estimate of the thermal energy of the bubbles as ∼8 × 1056 erg. This energy can be supplied by the jets and perhaps by the wind from the accretion flow of the galaxy's low-luminosity AGN, which most likely has been much more powerful in the recent past, with an average mechanical energy release rate of ∼4 × 1042 erg s−1 over the last ∼8 × 106 yr – the estimated age of the structure. We also show evidence for diffuse X-ray emission on larger scales, indicating the presence of a hot galactic corona. Our results provide a clear manifestation of galactic nuclear feedback regulating the gas content and energetics of the circumgalactic medium of disc galaxies similar to our own. [ABSTRACT FROM AUTHOR]

Here, we present the results of our multiwavelength campaign aimed at classifying Swift J170800−402551.8 as part of the Swift Deep Galactic Plane Survey (DGPS). We utilized Target of Opportunity (ToO) observations with the Neil Gehrels Swift Observatory, Chandra X-ray Observatory , Neutron star Interior Composition Explorer (NICER), X-ray Multi-Mirror Mission (XMM–Newton), Nuclear Spectroscopic Telescope Array (NuSTAR), and the Southern African Large Telescope (SALT), as well as multiwavelength archival observations from Gaia , VST Photometric Hα Survey, and VISTA Variables in the Via Lactea. The source displays a periodicity of 784 s in our XMM–Newton observation. The X-ray spectrum (XMM–Newton and NuSTAR) can be described by thermal bremsstrahlung radiation with a temperature of kT ≈ 30 keV. The phase-folded X-ray light curve displays a double-peaked, energy-dependent pulse profile. We used Chandra to precisely localize the source, allowing us to identify and study the multiwavelength counterpart. Spectroscopy with SALT identified a Balmer H α line, and potential He  i lines, from the optical counterpart. The faintness of the counterpart (r ≈ 21 AB mag) favours a low-mass donor star. Based on these criteria, we classify Swift J170800−402551.8 as a candidate intermediate polar cataclysmic variable, where the spin period of the white dwarf is 784 s. [ABSTRACT FROM AUTHOR]

We present the results obtained from follow-up observations of the MUSE Ultra Deep Field (MUDF) at X-ray energies with XMM–Newton. The MUDF is centred on a unique field with two bright, physically associated quasars at z ≃ 3.23, separated by ∼500 kpc in projection. Both quasars are embedded within extended Lyα nebulae (⁠|${\gtrsim}100\,{\rm kpc}$| at a surface brightness flux level of ≈6 × 10−19  |${\rm erg\,s^{-1}\,cm^{-2}\,arcsec^{-2}}$|⁠), whose elongated morphology is suggestive of an extended filament connecting the quasar haloes. The new X-ray observations presented here allow us to characterize the physical properties (e.g. X-ray slope, luminosities, gas column densities) in the innermost region of the MUDF quasars. We find that both quasars are X-ray underluminous compared to objects at similar ultraviolet luminosities. Based on our X-ray spectral analysis, absorbing columns of N H(z) ≳ 1023 cm−2 appear unlikely therefore such a weakness is possibly intrinsic. When also including literature data, we do not observe any detectable trend between the area of the nebulae and nuclear luminosities at both the rest-frame 2 keV and 2500 Å. The area is also not correlated with the X-ray photon index nor with the integrated band flux in the hard band (2–10 keV). We also do not find any trend between the extended Lyα emission of the nebulae and the nuclear X-ray luminosity. Finally, the properties of the MUDF quasars' nebulae are consistent with the observed relation between the Lyα integrated luminosity of the nebulae and their area. Our results suggest that the quasar ionization power is not a strong driver of the morphology and size of the nebulae. [ABSTRACT FROM AUTHOR]

XMM‐Newton, a European Space Agency observatory, has been observing the X‐ray, ultra‐violet, and optical sky for 23 years. During this time, astronomy has evolved from mainly studying single sources to populations and from a single wavelength, to multi‐wavelength/messenger data. We are also moving into an era of time domain astronomy. New software and methods are required to accompany evolving astronomy and prepare for the next‐generation X‐ray observatory, Athena. Here we present XMM2ATHENA, a program funded by the European Union's Horizon 2020 research and innovation program. XMM2ATHENA builds on foundations laid by the XMM‐Newton Survey Science Centre (XMM‐SSC), including key members of this consortium and the Athena Science ground segment, along with members of the X‐ray community. The project is developing and testing new methods and software to allow the community to follow the X‐ray transient sky in quasi‐real time, identify multi‐wavelength/messenger counterparts of XMM‐Newton sources and determine their nature using machine learning. We detail here the first milestone delivery of the project, a new online, sensitivity estimator. We also outline other products, including the forthcoming innovative stacking procedure and detection algorithms, to detect the faintest sources. These tools will then be adapted for Athena and the newly detected/identified sources will enhance preparation for observing the Athena X‐ray sky. [ABSTRACT FROM AUTHOR]

We present the first X-ray observation at sub-arcsecond resolution of the high-redshift (z  = 6.18) radio-loud quasar CFHQS J142952 + 544717 (J1429). The ∼100 net-count 0.3–7 keV spectrum obtained from ∼30 ks Chandra exposure is best fit by a single power-law model with a photon index Γ = 2.0 ± 0.2 and no indication of an intrinsic absorber, implying a 3.6–72 keV rest-frame luminosity |$L_{\rm X}=(2.3^{+0.6}_{-0.5})\times 10^{46}$|  erg s−1. We identify a second X-ray source at 30″ distance from J1429 position, with a soft (Γ ≃ 2.8) and absorbed (equivalent hydrogen column density N H < 13.4 × 1020 cm−2) spectrum, which likely contaminated J1429 spectra obtained in lower angular resolution observations. Based on the analysis of the Chandra image, the bulk of the X-ray luminosity is produced within the central ∼3 kpc region, either by the disc/corona system, or by a moderately aligned jet. In this context, we discuss the source properties in comparison with samples of low- and high-redshift quasars. We find indication of a possible excess of counts over the expectations for a point-like source in a 0.5″–1.5″ (∼3−8 kpc) annular region. The corresponding X-ray luminosity at J1429 redshift is 4 × 1045 erg s−1. If confirmed, this emission could be related to either a large-scale X-ray jet, or a separate X-ray source. [ABSTRACT FROM AUTHOR]

While hot ICM in galaxy clusters makes these objects powerful X-ray sources, the cluster's outskirts and overdense gaseous filaments might give rise to much fainter sub-keV emission. Cosmological simulations show a prominent 'focusing' effect of rich clusters on the space density of the warm-hot intergalactic medium (WHIM) filaments up to a distance of |$\sim 10\, {\rm Mpc}$| (∼ turnaround radius, rta) and beyond. Here, we use Magneticum simulations to characterize their properties in terms of integrated emission measure for a given temperature and overdensity cut and the level of contamination by the more dense gas. We suggest that the annuli |$(\sim 0.5-1)\times \, r_{ta}$| around massive clusters might be the most promising sites for the search of the gas with overdensity ≲ 50. We model spectral signatures of the WHIM in the X-ray band and identify two distinct regimes for the gas at temperatures below and above |$\sim 10^6\, {\rm K}$|⁠. Using this model, we estimate the sensitivity of X-ray telescopes to the WHIM spectral signatures. We found that the WHIM structures are within reach of future high spectral resolution missions, provided that the low-density gas is not extremely metal-poor. We then consider the Coma cluster observed by SRG/eROSITA during the CalPV phase as an example of a nearby massive object. We found that beyond the central r ∼ 40 arcmin (⁠|$\sim 1100\, {\rm kpc}$|⁠) circle, where calibration uncertainties preclude clean separation of the extremely bright cluster emission from a possible softer component, the conservative upper limits are about an order of magnitude larger than the levels expected from simulations. [ABSTRACT FROM AUTHOR]

We present new results from INTEGRAL and Swift observations of the hitherto poorly studied and unidentified X-ray source XTE J1906+090. A bright hard X-ray outburst (luminosity of ∼1036 erg s−1 above 20 keV) has been discovered with INTEGRAL observations in 2010, this being the fourth outburst ever detected from the source. Such events are sporadic, the source duty cycle is in the range (0.8–1.6) per cent as inferred from extensive INTEGRAL and Swift monitoring in a similar hard X-ray band. Using five archival unpublished Swift /X-Ray Telescope (XRT) observations, we found that XTE J1906+090 has been consistently detected at a persistent low X-ray luminosity value of ∼1034 erg s−1, with limited variability (a factor as high as 4). Based on our findings, we propose that XTE J1906+090 belongs to the small and rare group of persistent low-luminosity Be X-ray binaries. [ABSTRACT FROM AUTHOR]

SMSS J114447.77-430859.3 (z  = 0.83) has been identified in the SkyMapper Southern Survey as the most luminous quasar in the last |$\sim 9\, \rm Gyr$|. In this paper, we report on the eROSITA/ Spectrum–Roentgen–Gamma (SRG) observations of the source from the eROSITA All Sky Survey, along with presenting results from recent monitoring performed using Swift ,  XMM-Newton , and NuSTAR. The source shows a clear variability by factors of ∼10 and ∼2.7 over time-scales of a year and of a few days, respectively. When fit with an absorbed power law plus high-energy cutoff, the X-ray spectra reveal a Γ = 2.2 ± 0.2 and |$E_{\rm cut}=23^{+26}_{-5}\, \rm keV$|. Assuming Comptonization, we estimate a coronal optical depth and electron temperature of |$\tau =2.5-5.3\, (5.2-8)$| and |$kT=8-18\, (7.5-14)\, \rm keV$| , respectively, for a slab (spherical) geometry. The broadband SED is successfully modelled by assuming either a standard accretion disc illuminated by a central X-ray source, or a thin disc with a slim disc emissivity profile. The former model results in a black hole mass estimate of the order of |$10^{10}\, \mathrm{ M}_\odot$| , slightly higher than prior optical estimates; meanwhile, the latter model suggests a lower mass. Both models suggest sub-Eddington accretion when assuming a spinning black hole, and a compact (⁠|$\sim 10\, r_{\rm g}$|) X-ray corona. The measured intrinsic column density and the Eddington ratio strongly suggest the presence of an outflow driven by radiation pressure. This is also supported by variation of absorption by an order of magnitude over the period of |$\sim 900 \ \rm d$|. [ABSTRACT FROM AUTHOR]

X-ray radiation, in particular radiation between 0.1 and 10 keV, is evident from both point-like sources, such as compact objects and T-Tauri young stellar objects, and extended emission from hot, cooling gas, such as in supernova remnants. The X-ray radiation is absorbed by nearby gas, providing a source of both heating and ionization. While protoplanetary chemistry models now often include X-ray emission from the central young stellar object, simulations of star-forming regions have yet to include X-ray emission coupled to the chemo-dynamical evolution of the gas. We present an extension of the treeray reverse ray trace algorithm implemented in the flash magnetohydrodynamic code which enables the inclusion of X-ray radiation from 0.1 keV < E γ < 100 keV, dubbed xraythespot. xraythespot allows for the use of an arbitrary number of bins, minimum and maximum energies, and both temperature-independent and temperature-dependent user-defined cross-sections, along with the ability to include both point and extended diffuse emission and is coupled to the thermochemical evolution. We demonstrate the method with several multibin benchmarks testing the radiation transfer solution and coupling to the thermochemistry. Finally, we show two example star formation science cases for this module: X-ray emission from protostellar accretion irradiating an accretion disc and simulations of molecular clouds with active chemistry, radiation pressure, and protostellar radiation feedback from infrared to X-ray radiation. [ABSTRACT FROM AUTHOR]

Jupiter's disc is bright in X-rays as H2 molecules in the atmosphere are very effective at scattering solar X-rays. K-shell fluorescence from carbon atoms in atmospheric methane is thought to also provide a minor contribution. XMM–Newton has now observed Jupiter over a span of nearly two solar cycles from 2003 to 2021, offering the opportunity to determine whether Jupiter's disc emissions are driven by solar activity or not. We compare the count rates of X-rays of energies 0.2–10.0, 0.2–2.0, 2.1–5.0, and 5.1–10.0 keV from the planet's equatorial region, with the sunspot number and F10.7 adjusted solar radio flux. The respective Pearson's correlation coefficients for both are 0.88/0.84, 0.86/0.83, 0.40/0.34, and 0.29/0.22 for each energy demonstrating that the low-energy X-ray disc emissions are indeed controlled by the Sun's activity. This relationship is less clear for the higher energy emissions, raising questions around the source of these emissions. [ABSTRACT FROM AUTHOR]

We report the discovery of a candidate X-ray supernova remnant SRGe J003602.3+605421 = G121.1−1.9 in the course of the SRG /eROSITA all-sky survey. The object is located at (l, b) = (121.1°, −1.9°), is ≈36 arcmin in angular size, and has a nearly circular shape. Clear variations in the spectral shape of the X-ray emission across the object are detected, with the emission from the inner (within 9 arcmin) and outer (9–18 arcmin) parts dominated by iron and oxygen/neon lines, respectively. The non-equilibrium plasma emission model is capable of describing the spectrum of the outer part with an initial gas temperature 0.1 keV, final temperature 0.5 keV, and ionization age ∼2 × 1010 cm−3 s. The observed spectrum of the inner region is more complicated (plausibly due to the contribution of the outer shell) and requires a substantial overabundance of iron for all models that we have tried. The derived X-ray absorption is equal to (4–6) × 1021 cm−2, locating the object at a distance beyond 1.5 kpc, and implying its age ∼(5–30) × 1000 yr. No bright radio, infrared, H α, or gamma-ray counterpart of this object has been found in the publicly available archival data. A model invoking a canonical 1051 erg explosion (either SN Ia or core collapse) in the hot and tenuous medium in the outer region of the Galaxy ∼9 kpc away might explain the bulk of the observed features. This scenario can be tested with future deep X-ray and radio observations. [ABSTRACT FROM AUTHOR]

The European Space Agency is studying two large-class missions bound to operate in the decade of the 30s, and aiming at investigating the most energetic and violent phenomena in the Universe. Athena is poised to study the physical conditions of baryons locked in large-scale structures from the epoch of their formation, as well as to yield an accurate census of accreting supermassive black holes down to the epoch of reionization; LISA will extend the hunt for Gravitational Wave (GW) events to the hitherto unexplored mHz regime. We discuss in this paper the science that their concurrent operation could yield, and present possible Athena observational strategies. We focus on Supermassive (M |$\lesssim 10^7\, \rm {M_\odot }$|⁠) Black Hole Mergers (SMBHMs), potentially accessible to Athena up to z ∼ 2. The simultaneous measurement of their electromagnetic (EM) and GW signals may enable unique experiments in the domains of astrophysics, fundamental physics, and cosmography, such as the magnetohydrodynamics of fluid flows in a rapidly variable space–time, the formation of coronae and jets in Active Galactic Nuclei, and the measurement of the speed of GW, among others. Key to achieve these breakthrough results will be the LISA capability of locating a SMBHM event with an error box comparable to, or better than the field-of-view of the Athena Wide Field Imager (⁠|$\simeq 0.4\,$|  deg2) and Athena capability to slew fast to detect the source during the inspiral phase and the post-merger phase. Together, the two observatories will open in principle the exciting possibility of truly concurrent EM and GW studies of the SMBHMs [ABSTRACT FROM AUTHOR]

We present the new X‐ray functionalities of the skirt radiative transfer code, forming an advanced tool to study cold dusty gas in active galactic nuclei (AGN), with a particular focus on complex three‐dimensional transfer media. Focusing on the X‐ray broadband spectra of obscured AGN, skirt incorporates scattering on free electrons, absorption and fluorescence by cold gas, scattering on bound electrons, as well as absorption and scattering by dust. This goes beyond the X‐ray physical processes that are currently implemented in most spectral models for fitting distant reflection in AGN. With the introduction of these X‐ray physics, we obtain a high‐performance radiative transfer code that can model intricate multi‐phase AGN media with complex geometries in X‐rays, which furthermore supports advanced kinematics and allows for self‐consistent model predictions from infrared to X‐ray energies. [ABSTRACT FROM AUTHOR]

A large number of unidentified sources found by astronomical surveys and other observations necessitate the use of an automated classification technique based on machine learning (ML) methods. The aim of this paper is to find a suitable automated classifier to identify the point X-ray sources in the Chandra Source Catalogue (CSC) 2.0 in the categories of active galactic nuclei (AGN), X-ray emitting stars, young stellar objects (YSOs), high-mass X-ray binaries (HMXBs), low-mass X-ray binaries (LMXBs), ultra luminous X-ray sources (ULXs), cataclysmic variables (CVs), and pulsars. The catalogue consists of ≈317 000 sources, out of which we select 277 069 point sources based on the quality flags available in CSC 2.0. In order to identify unknown sources of CSC 2.0, we use MW features, such as magnitudes in optical/ultraviolet bands from Gaia-EDR3, Sloan Digital Sky Survey, and GALEX, and magnitudes in infrared bands from 2MASS, WISE, and MIPS-Spitzer, in addition to X-ray features (flux and variability) from CSC 2.0. We find the Light Gradient Boosted Machine, an advanced decision tree-based ML classification algorithm, suitable for our purpose and achieve 93  per  cent precision, 93  per  cent recall score, and 0.91 Mathew's Correlation coefficient score. With the trained classifier, we identified 54 770 (14 066) sources with more than 3σ (4σ) confidence, out of which there are 32 600 (8574) AGNs, 16,148 (5,166) stars, 5,184 (208) YSOs, 439 (46) HMXBs, 197 (71) LMXBs, 50 (0) ULXs, 89 (1) CVs, and 63 (0) pulsars. This method can also be useful for identifying sources of other catalogues reliably. [ABSTRACT FROM AUTHOR]

The diffuse Fe XXV (6.7 keV) line emission observed in the Galactic ridge is widely accepted to be produced by a superposition of a large number of unresolved X-ray point sources. In the very central degrees of our Galaxy, however, the existence of an extremely hot (~7 keV) diffuse plasma is still under debate. In this work we measure the Fe XXV line emission using all available XMM-Newton observations of the Galactic centre (GC) and inner disc (−10° < ℓ < 10°, −2° < b < 2°). We use recent stellar mass distribution models to estimate the amount of X-ray emission originating from unresolved point sources, and find that within a region of ℓ = ±1° and b = ±0.25° the 6.7keV emission is 1.3–1.5 times in excess of what is expected from unresolved point sources. The excess emission is enhanced towards regions where known supernova remnants are located, suggesting that at least a part of this emission is due to genuine diffuse very hot plasma. If the entire excess is due to very hot plasma, an energy injection rate of at least ~6 × 1040 erg s−1 is required, which cannot be provided by the measured supernova explosion rate or past Sgr A* activity alone. However, we find that almost the entire excess we observe can be explained by assuming GC stellar populations with iron abundances ~1.9 times higher than those in the bar/bulge, a value that can be reproduced by fitting diffuse X-ray spectra from the corresponding regions. Even in this case, a leftover X-ray excess is concentrated within ℓ = ±0.3° and b = ±0.15°, corresponding to a thermal energy of ~2 × 1052 erg, which can be reproduced by the estimated supernova explosion rate in the GC. Finally we discuss a possible connection to the observed GC Fermi-LAT excess. [ABSTRACT FROM AUTHOR]

Context. The current observational status of the hot (log T(K) > 5.5) intergalactic medium (IGM) remains incomplete. While recent X-ray emission and Sunyaev-Zeldovich effect observations from stacking large numbers of Cosmic Web filaments have yielded statistically significant detections of this phase, direct statistically significant measurements of single objects remain scarce. The lack of such a sample currently prevents a robust analysis of the cosmic baryon content composed of the hot IGM, which would potentially help solve the cosmological missing baryons problem. Aims. In order to improve the observationally challenging search for the missing baryons, we utilise the theoretical avenue afforded by the EAGLE simulations. Our aim is to get insights into the metal enrichment of the Cosmic Web and the distribution of highly ionised metals in the IGM. Our goal is to aid in the planning of future X-ray observations of the hot intergalactic plasma. Methods. We detected the filamentary network by applying the Bisous formalism to galaxies in the EAGLE simulation. We characterised the spatial distributions of oxygen and O VII and studied their mass and volume filling fractions in the filaments. Since oxygen is formed in and expelled from galaxies, we also studied the surroundings of haloes. We used this information to construct maps of the O VII column density and determine the feasibility of detecting it via absorption with Athena X-IFU. Results. Within EAGLE, the oxygen and O VII number densities drop dramatically beyond the virial radii of haloes. In the most favourable scenario, the median extent of O VII above the Athena X-IFU detection limit is ≈700 kpc. Since galaxies are relatively far apart from one another, only ∼1% of the filament volumes are filled with O VII at high enough column densities to be detectable by X-IFU. The highly non-homogeneous distribution of the detectable O VII complicates the usage of the measurements of the intergalactic O VII absorbers for tracing the missing baryons and estimating their contribution to the cosmic baryon budget. Instead, the detectable volumes form narrow and dense envelopes around haloes, while the rest of the O VII is diluted at low densities within the full filament volumes. This localised nature, in turn, results in a low chance (∼10−20% per sight line) of detecting intergalactic O VII with Athena X-IFU within the observational SDSS catalogue of nearby filaments. Fortunately, with deeper filament samples, such as those provided via the future 4MOST 4HS survey, the chances of intercepting an absorbing system are expected to increase up to a comfortable level of ∼50% per sight line. Conclusions. Based on EAGLE results, targeting the Cosmic Web with Athena may only result in tip-of-the-iceberg detections of the intergalactic O VII, which is located in the galaxy outskirts. This would not be enough to conclusively solve the missing baryon problem. However, the projection of many filaments into a single line of sight will enable a useful X-ray observation strategy with Athena X-IFU for the hot cosmic baryon gas, reducing the amount of baryons still missing by up to ∼25%. [ABSTRACT FROM AUTHOR]

Solar wind (SW) charge exchange (CX) is an important mechanism responsible for X-ray emissions in comets' coma and many other astrophysical environments. By incorporating the experimentally derived total cross-sections and the tested state-selectivity models into the Kronos program, we generate X-ray spectra in H-like and fully stripped C, N, O ion CX collision with atomic H. Using these data, we revisit the fitting of Chandra X-ray data of Comet C/1999 S4 by considering the typical SW collision energies of 0.8 and 3 keV/u, respectively. Our results are in an excellent agreement with the astrophysical observation. We find that charge exchange between C5+,6+, N6+,7+, O7+,8+ and H significantly contributes to the comet's spectrum ranging from 300 to 800 eV for both slow and fast SW ions, where N7+ abundance is underestimated in previous studies. [ABSTRACT FROM AUTHOR]

We present a systematic study of the unbinned, photon-by-photon likelihood technique which can be used as an alternative method to analyse phase-dependent, X-ray spectro-polarimetric observations obtained with IXPE and other photoelectric polarimeters. We apply the unbinned technique to models of the luminous X-ray pulsar Hercules X-1, for which we produce simulated observations using the ixpeobssim package. We consider minimal knowledge about the actual physical process responsible for the polarized emission from the accreting pulsar and assume that the observed phase-dependent polarization angle can be described by the rotating vector model. Using the unbinned technique, the detector's modulation factor, and the polarization information alone, we found that both the rotating vector model and the underlying spectro-polarimetry model can reconstruct equally well the geometric configuration angles of the accreting pulsar. However, the measured polarization fraction becomes biased with respect to the underlying model unless the energy dispersion and effective area of the detector are also taken into account. To this end, we present an energy-dispersed likelihood estimator that is proved to be unbiased. For different analyses, we obtain posterior distributions from multiple ixpeobssim realizations and show that the unbinned technique yields |$\sim 10{{\ \rm per\ cent}}$| smaller error bars than the binned technique. We also discuss alternative sources, such as magnetars, in which the unbinned technique and the rotating vector model might be applied. [ABSTRACT FROM AUTHOR]

We present a study of optically selected dual Active Galactic Nuclei (AGN) with projected separations of 3–97 kpc. Using multiwavelength (MWL) information (optical, X-ray, mid-IR), we characterized the intrinsic nuclear properties of this sample and compared them with those of isolated systems. Among the 124 X-ray-detected AGN candidates, 52 appear in pairs and 72 as single X-ray sources. Through MWL analysis, we confirmed the presence of the AGN in >80 per cent of the detected targets in pairs (42 out of 52). X-ray spectral analysis confirms the trend of increasing AGN luminosity with decreasing separation, suggesting that mergers may have contributed to triggering more luminous AGN. Through X-ray/mid-IR ratio versus X-ray colours, we estimated a fraction of Compton-thin AGN (with 1022 cm−2 < N H < 1024 cm−2) of about 80 per cent, while about 16 per cent are Compton-thick sources (with N H > 1024 cm−2). These fractions of obscured sources are larger than those found in samples of isolated AGN, confirming that pairs of AGN show higher obscuration. This trend is further confirmed by comparing the de-reddened [O  iii ] emission with the observed X-ray luminosity. However, the derived fraction of Compton-thick sources in this sample at the early stages of merging is lower than that reported for late-merging dual-AGN samples. Comparing N H from X-rays with that derived from E (B − V) from narrow-line regions, we found that the absorbing material is likely to be associated with the torus or broad-line regions. We also explored the X-ray detection efficiency of dual-AGN candidates, finding that, when observed properly (at on-axis positions and with long exposures), X-ray data represent a powerful way to confirm and investigate dual-AGN systems. [ABSTRACT FROM AUTHOR]

Flux-resolved X-ray spectroscopy is widely adopted to investigate the spectral variation of a target between various flux levels. In many cases, it is done through horizontally splitting a single light curve into multiple flux levels with certain count-rate threshold(s). In this work, we point out there are two hidden biases in this approach that could affect the spectral analyses under particular circumstances. The first is that when Poisson fluctuations of the source counts in light curve bins are non-negligible compared with the intrinsic variation, this approach would overestimate (underestimate) the intrinsic average flux level of the high (low) state. The second bias is that when the Poisson fluctuations of the background count rate is non-negligible, the background spectrum of the high (low) state would be underestimated (overestimated), thus yielding biased spectral fitting parameters. We take NuSTAR spectra, for example, to illustrate the effects of the biases, and particularly how the measurements of the coronal temperature in active galactic nuclei would be biased. We present a toy method to assess the significance of such biases and approaches to correct for them when necessary. [ABSTRACT FROM AUTHOR]

Context. Nowadays, we know that the origin of the cosmic X-ray background (CXB) is mainly due to the integrated emission of active galactic nuclei. Therefore, in order to obtain a precise estimate of the contribution of different source classes to the CXB, it is crucial to achieve full characterization of the hard-X ray sky. Aims. We present a multifrequency analysis of all sources listed in the third release of the Palermo Swift-BAT hard X-ray catalog (3PBC) with the goal of (i) identifying and classifying the largest number of sources adopting multifrequency criteria, with particular emphasis on extragalactic populations and (ii) extracting sources belonging to the class of Seyfert galaxies to present here the release of the second version of the Turin-SyCAT. Methods. We outline a classification scheme based on radio, infrared (IR), and optical criteria that allows us to distinguish between unidentified and unclassified hard X-ray sources, as well as to classify those sources belonging to the Galactic and the extragalactic populations. Results. Our revised version of the 3PBC lists 1176 classified, 820 extragalactic, and 356 Galactic sources, as well as 199 unclassified and 218 unidentified sources. According to our analysis, the hard X-ray sky is mainly populated by Seyfert galaxies and blazars. For the blazar population, we report trends between the hard X-ray and the gamma-ray emissions based on the fact that a large fraction of them also have a counterpart detected by the Fermi satellite. These trends are all in agreement with the expectations of inverse Compton models which are widely adopted to explain the blazar broadband emission. For the Seyfert galaxies, we present the second version of the Turin-SyCAT, including a total of 633 Seyfert galaxies, with 282 new sources corresponding to an increase of ~80% with respect to the previous release. Comparing the hard X-ray and the infrared emissions of Seyfert galaxies, we confirm that there is no clear difference between the flux distribution of the infrared-to-hard X-ray flux ratio of Seyfert galaxies Type 1 and Type 2. However, there is a significant trend between the mid-IR flux and hard X-ray flux, confirming previous statistical results in the literature. Conclusions. We provide two catalog tables. The first is the revised version of the 3PBC catalog based on our multifrequency analyses. The second catalog table is a release of the second version of the Turin-SyCAT catalog. Finally, we highlight that extensive soft X-ray data are already available in the form of the Swift archive which can be used to search for potential counterparts of unidentified hard X-ray sources. All these datasets will be reduced and analyzed in a forthcoming analysis to determine the precise position of low-energy counterparts in the 0.5–10 keV energy range for 3PBC sources that can be targets of future optical spectroscopic campaigns; this is necessary to obtain their precise classification. [ABSTRACT FROM AUTHOR]