Chandreyee Maitra

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 ~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.

We report the discovery of a bow-shock pulsar wind nebula (PWN), dubbed Thunder, powered by the radio pulsar PSR J1631−4722 and projected within the Galactic supernova remnant (SNR) G336.7+0.5 (Nimbus). The system was first identified in observations from the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe survey and further characterized using MeerKAT Galactic Plane Survey data, together with follow-up observations at 5.5 and 9 GHz obtained with the Australia Telescope Compact Array. Assuming a distance of 7 kpc, the radio images resolve an elongated ∼80″ (2.7 pc) cometary nebula, indicative of a high-velocity pulsar. An X-ray counterpart extending ∼50″ (1.7 pc) is detected in archival XMM-Newton data. The flat radio spectrum ( α = −0.27 ± 0.05) and hard X-ray photon index (Γ = 1.6 ± 0.4) indicate synchrotron emission from relativistic particles injected in the pulsar wind. Polarization analysis reveals a highly ordered magnetic field aligned with the nebular flow, with fractional polarization reaching up to 30% in the tail. An equipartition estimate gives a PWN magnetic field strength of B _eq ≈ 54–140 μ G. Pulsar timing over a ∼2.2 yr baseline reveals strong timing noise and a small spin glitch with amplitude Δ ν / ν = 1.10 × 10 ⁻⁸ . The SNR shows no clear diffuse X-ray counterpart. The morphology and multiwavelength properties of the Nimbus–Thunder system, together with evolutionary models, constrain the system age to ∼30–45 kyr, placing the remnant in the late Sedov phase, approaching the transition to the radiative stage.

We present timing and spectral analysis of the recently identified ultracompact double-degenerate (DD) white dwarf binary eRASSU J060839.5–704014 using observations from NICER and Einstein Probe (EP), together with archival XMM-Newton data. By phase-connecting the long-term XMM-Newton, NICER, and EP observations, we obtain a coherent quadratic timing solution, yielding an orbital period of 374.15013 (2) s and an orbital decay rate of P ̇ = − 4.7 ( 1 ) × 1 0 − 11 s s − 1 . This orbital decay exceeds that measured in the prototypical DD binaries HM Cnc and V407 Vul. Assuming that the observed orbital evolution is primarily driven by gravitational-wave (GW) angular momentum loss, the inferred chirp mass is ∼0.43 M _⊙ , placing the source among the most massive known systems of this class. The phase-averaged spectra of NICER and EP-Follow-up X-ray Telescope (FXT) are described by a soft thermal component with temperatures of ∼126 and ∼144 eV, respectively, confirming the supersoft nature of the source. Phase-resolved spectroscopy reveals a clear decrease in temperature across the bright phase in both instruments, indicating a structured emission region with significant temperature gradients. These results establish eRASSU J060839.5–704014 as one of the most rapidly evolving ultracompact DD binaries presently known, belonging to the rare class of direct-impact ultracompact binaries, and a promising verification source for future low-frequency GW studies.

The Sloan Digital Sky Survey-V (SDSS-V) Magellanic Genesis Survey is a spectroscopic program designed to map the kinematic and chemical structure of the Magellanic Clouds (MCs) using APOGEE and BOSS spectroscopy. This overview describes the survey’s design, target selection, and science goals and highlights some first results using these data. In the inner regions of the Large and Small Magellanic Clouds (LMC and SMC), the survey obtained high-resolution near-infrared APOGEE spectra (S/N ≈ 45) of ∼14,000 bright, oxygen-rich asymptotic giant branch (AGB-O) stars. These data provide contiguous spatial coverage of the MCs’ main bodies, enabling detailed chemodynamical studies. To explore extended structures, the survey includes BOSS optical spectroscopy of fainter red giant stars selected with Gaia DR3 data, reaching G ≈ 17.5. Many of these targets extend to the outer regions of the MCs, which are known to span ∼20° (LMC) and ∼12° (SMC) and contain diffuse substructures of unclear origin. BOSS data in the inner regions also complement APOGEE by providing elements inaccessible in the near-infrared and enabling cross-calibration between instruments. The survey further includes APOGEE and BOSS observations of ∼300 evolved massive stars and a small sample of symbiotic binaries previously observed by APOGEE-1 and APOGEE-2, enhancing our understanding of massive stellar evolution and complementing the SDSS-V main-sequence massive star program.

Ultraluminous X-ray sources (ULXs) are luminous non-nuclear X-ray point sources embedded in galaxies. Their luminosities exceeding 10^ 39 , , ^ erg s -1 potentially require sub-Eddington accretion by objects with masses from ∼10^2,M_⊙ to ∼10^4,M_⊙ or supercritical accretion beyond the Eddington limit by stellar mass black holes or neutron stars. As such, ULXs are excellent laboratories for extreme accretion flows in X-ray binaries and, in some cases, potential candidates for intermediate-mass black holes. The first catalog by the eROSITA instrument on board the Spectrum-Roentgen-Gamma mission provides the most complete X-ray view of the whole of the western Galactic hemisphere and is therefore an excellent resource in which to find new ULXs. We identified ULXs by searching for X-ray counterparts in the ∼10^5 local galaxies of the catalog in the footprint of the first eROSITA all-sky survey. The catalog is unaffected by X-ray selection biases. We characterized the completeness of the sample and its contamination by unidentified active galactic nuclei (AGN) and determined the influence of source confusion. The catalog provides the basis for ULX population studies and follow-up observations that can be used to perform a more detailed investigation of individual sources and variability. HECATE We searched for X-ray point sources exceeding the ULX threshold in HECATE galaxies while excluding the nuclear regions of the galaxies to avoid the selection of AGN. We removed known contaminants such as supernovae, stars, and AGN, and we manually vetted all candidates to further remove potential contaminants. We derived the X-ray selection function and fraction of unidentified AGN interlopers using a simulation with subsequent source detection. By comparing our sample to other ULX catalogs, we identified previously unknown candidates and those not detected although expected from their flux, indicating source intrinsic variability. We present two samples of ULX candidates. The main sample consists of 90 sources with highly confident X-ray detections, 53 of which are identified for the first time. This sample is complete to a distance of ∼7, contains at most 29% of unknown background AGN, and is mostly unaffected by source confusion. Several candidates are newly identified even though their locations have been observed by other instruments before, and some previously reported candidates we expected to identify are absent from our sample, demonstrating the transient behavior of ULXs. Based on our list of less confident detections, we also provide an extended catalog of 260 sources identified as potential candidates for further ULX identifications. Of these, 245 are identified as potential candidates for the first time.

In a search for radio nebulae with a low surface brightness within the ASKAP-EMU survey, we discovered a faint radio shell, G289.6+5.8, and its central point radio source at the position of the soft γ -ray source IGR J11187-5438. The central radio source is spatially coincident with a previously known low-mass X-ray binary (LMXB) with an M-type donor star. However, the newly determined Gaia DR3 distance of 267 pc and correspondingly low X-ray luminosity (3×10 ³¹ erg s ⁻¹ ) cast doubt on the LMXB classification. Neither radio nor X-ray pulsations are detected. Chance alignments between radio shell, central radio source, optical star, γ -ray, and X-ray sources appear unlikely. By combining all currently available evidence, we conclude that G289.6+5.8 is a remnant of a low-energy core-collapse explosion of an intermediate-mass star (~8M _⊙ ) in a binary system with an M-type secondary that remained bound after the explosion. In this scenario, G289.6+5.8 is a supernova remnant, while the central γ - and X-ray source is associated with a young neutron star whose pulsar wind interacts with its M-type stellar companion, making IGR J11187-5438 a nascent spider-type X-ray binary.

Aims. Supernova remnants (SNRs) are responsible for the injection of energy and chemical elements into the interstellar medium (ISM). The emission from SNRs can be studied to infer information about the supernova (SN) explosion itself as well as about the properties of the surrounding ISM. Studying a sample of SNRs in a galaxy provides an opportunity to better understand stellar feedback, and the best laboratory for such an investigation is the Large Magellanic Cloud (LMC). The LMC is the nearest star-forming galaxy, it lies outside the Galactic plane line of sight, and therefore its foreground absorption is low. Methods. The eROSITA telescopes are the best instruments currently available to perform a survey of the SNRs in the entire LMC due to their large field of view and their high sensitivity towards soft X-rays. We used the sample of SNRs reported in the previous paper and performed a spectral analysis on a part of the sample. We estimated the flux and the luminosity of the fainter sources using the energy conversion factor obtained assuming a non-equilibrium ionisation plasma model. Results. The X-ray luminosity function (XLF) of SNRs in the LMC shows a relatively large number of SNRs at high luminosities. We fitted the distribution with two Gaussian components, which yielded best-fit maxima for the L _X [0.3-8.0keV] distribution at m ₁ = 10 ^34.7±0.2 erg s ⁻¹ and m ₂ = 10 ^36.5±0.4 erg s ⁻¹ . We compared the XLF of the LMC with the XLFs of the Small Magellanic Cloud (SMC), M31, and M33 using a power-law fit and an Anderson-Darling (DA) test. The power indices of the XLFs of the LMC and SMC appear consistent with each other, while those of M33 and M31 are larger. Thus, the latter have steeper power laws, indicating a lower number of X-ray luminous SNRs with respect to the Magellanic Clouds. The DA test showed that the luminosity distributions of SNRs in the SMC and LMC are compatible with being extracted from the same underlying distribution. They are also compatible for different galaxies if we consider the same lower limit for L _X [0.3-8.0 keV] for the entire distribution. Finally, we compared the luminosity and the X-ray sizes (diameter) of the SNRs in our sample. We observed a general trend of anti-correlation between size and X-ray luminosity that can be interpreted as a result of fading with time.

Context . The Magellanic Clouds, the closest star-forming galaxies to the Milky Way, offer an excellent environment to study high-mass X-ray binaries (HMXBs). While the Small Magellanic Cloud (SMC) has been thoroughly investigated with over 120 systems identified, the Large Magellanic Cloud (LMC) has lacked a complete survey due to its large angular size. Most prior studies targeted central or high-star-formation regions. The SRG /eROSITA all-sky surveys now enable a comprehensive coverage of the LMC, particularly due to its close vicinity to the south ecliptic pole. Aims . This work aims to improve our understanding of the HMXB population in the LMC by building a flux-limited catalogue. This allows us to compare sample properties with those of HMXB populations in other nearby galaxies. Methods . Using detections during the first eROSITA all-sky survey (eRASS1), we cross-matched X-ray positions with optical and infrared catalogues to identify candidate HMXBs. We assigned flags based on multi-wavelength follow-up observations and archival data, using properties of known LMC HMXBs. These flags defined confidence classes for our candidates. Results . We detect sources down to X-ray luminosities of a few 10 ³⁴ erg s ⁻¹ , resulting in a catalogue of 53 objects, including 28 confirmed HMXBs and 21 new eROSITA detections. Compared to the SMC, the LMC hosts fewer HMXBs and more systems with supergiant companions. We identify several likely supergiant systems, including a candidate supergiant fast X-ray transient with phase-dependent flares. We also find three Be stars with likely white dwarf companions. Two of the candidate Be/WD binaries show steady luminosities across four eROSITA scans, unlike the post-nova states seen in the majority of previous Be/WD reports. Conclusions . Our catalogue is the first to cover the entire LMC since the ROSAT era, providing a basis for statistical population studies. Using the HMXB population, we estimate the LMC star-formation rate to be (0.22 _−0.07 ^+0.06 ) M _⊙ yr ⁻¹ , which is in agreement with results using other tracers.

Context. After nearly a decade of quiescence, the transient Be/X-ray binary pulsar RX J0520.5–6932 underwent an outburst in 2024. We performed X-ray monitoring of the source with NICER and AstroSat near the peak of the event. Aims. Our primary objective was to investigate the energy and luminosity dependence of the pulsed emission, characterize the spin evolution, and study the broadband X-ray spectral properties of RX J0520.5–6932 during the outburst. Methods. We extracted light curves and spectra from NICER and AstroSat observations carried out during the outburst. Pulsations were detected using epoch-folding techniques, enabling a detailed study of pulse-profile evolution as a function of energy and intensity. Broadband spectral modeling was performed using simultaneous data from SXT, LAXPC, and NICER . The spectra from individual NICER observations were used to study spectral variability. Results. The AstroSat /LAXPC and NICER light curves reveal pronounced short-duration flaring activity lasting ∼400–700 s with enhancements in intensity by about a factor of two. The pulse profile exhibits a strong dependence on both energy and intensity, evolving from a simple single-peaked structure at low energies to complex multi-peaked shapes at intermediate energies and reverting to simpler morphologies at higher energies. Pulse profiles during the flares differ significantly from those in the persistent state, indicating changes in the pulsed beam pattern with a change in the intensity on a short timescale. Broadband spectral analysis revealed a soft excess and an emission feature at ∼1 keV likely arising from reprocessed emission in the accretion disk and fluorescence from Ne K and Fe L ions. Continuous NICER monitoring over nearly one orbital cycle enabled us to track spin evolution with accretion-driven spin-up and spectral variability in the soft X-ray band. Additionally, we observed a declining spin-up rate during the outburst, likely due to a gradual reduction in mass accretion rate. Conclusions. Our results provide a comprehensive view of the complex accretion dynamics in RX J0520.5–6932 during its 2024 outburst. The strong variability in pulse shape and spin behavior highlights rapid changes in the accretion geometry and torque as a function of accretion rate.