X-ray Point Sources Research Articles

Outflow from the very massive Wolf-Rayet binary Melnick 34

Melnick 34 (Mk\,34) is one of the most massive binary systems known and is one of the brightest X-ray point sources in the 30 Doradus region. We investigated the impact of this massive system on the surrounding interstellar medium (ISM) using the optical spectroscopic capabilities of the narrow-field mode (NFM) of the Multi-Unit Spectroscopic Explorer (MUSE). MUSE-NFM spatially resolved the ISM in the vicinity of Mk\,34 with a resolution comparable to that of the HST. The analysis of the N ii \,lambda \,6583 and S ii \,lambda \,6717 emission lines reveals a cone-like structure apparently originating from Mk\,34 and extending southeast. Electron density maps and radial velocity measurements of the ISM lines further support an outflow scenario traced by these emissions. While no clear northwestern counterpart to this outflow was observed, we note increased extinction in that direction, towards the R136 cluster. The ISM material along the projected diagonal of the outflow on both sides of Mk\,34 shows similar properties in terms of the emission line ratios seen in the Baldwin-Phillips-Terlevich diagram. These results are consistent across two observational epochs. Additionally, we examined the residual maps within a 0.5" radius of Mk\,34 after modeling and subtracting the point spread function. The observed variations in the residuals could potentially be linked to Mk\,34's known periodic behavior. However, further observations with appropriate cadence are needed to fully monitor the 155\,day periodicity of Mk\,34's X-ray emissions.

The ACT-DR5 MCMF galaxy cluster catalog

Galaxy clusters are useful cosmological probes and interesting astrophysical laboratories. As the cluster samples continue to grow in size, a deeper understanding of the sample characteristics and improved control of systematics becomes more crucial. For this analysis we created a new and larger ACT-DR5-based thermal Sunyaev–Zel’dovich Effect- (tSZE-) selected galaxy cluster catalog with improved control over sample purity and completeness. We employed the red sequence based cluster redshift and confirmation tool MCMF together with optical imaging data from the Legacy Survey DR-10 and infrared data from the WISE satellite to systematically identify true clusters from a new cluster candidate detection run on the ACT-DR5 dataset. The resulting ACT-DR5 MCMF sample contains 6,237 clusters with a residual contamination of 10.7%. This is an increase of 49% compared to the previous ACT-DR5 cluster catalog, making this new catalog the largest tSZE-selected cluster catalog to date. The zphot>1 subsample contains 703 clusters, three times more than in the previous ACT-DR5 catalog. Cross-matching the ACT-DR5 MCMF cluster catalog with a deeper tSZE sample from SPTpol 500d allows us to confirm the completeness and purity of the new ACT-DR5 MCMF sample. Cross-matching to the two largest X-ray-selected cluster samples, the all-sky RASS MCMF and the western Galactic hemisphere survey eRASS1, confirms the sample purity of the RASS MCMF sample and in the case of eROSITA eRASS1 reveals that 43% of the matched clusters are designated in eRASS1 as X-ray point sources rather than groups and clusters. Cross-correlating the ACT-DR5 MCMF cluster catalog with ACT-DR6 lensing maps results in a 16.4σ detection of Cosmic Microwave Background (CMB) lensing around the clusters, corresponding to the strongest signal found so far for a galaxy cluster sample. Repeating the measurement for the z > 1 cluster subsample yields a significance of 4.3σ, which is the strongest CMB lensing detection in a z>1 cluster sample to date.

A Deeper Look into eFEDS AGN Candidates in Dwarf Galaxies with Chandra

The ability to accurately discern active massive black holes (BHs) in nearby dwarf galaxies is paramount to understanding the origins and processes of “seed” BHs in the early Universe. We present Chandra X-ray Observatory observations of a sample of three local dwarf galaxies (M * ≤ 3 × 109 M ⊙, z ≤ 0.15) previously identified as candidates for hosting active galactic nuclei (AGN). The galaxies were selected from the NASA-Sloan Atlas with spatially coincident X-ray detections in the eROSITA Final Equatorial Depth Survey. Our new Chandra data reveal three X-ray point sources in two of the target galaxies with luminosities between log(L 2−10 keV [erg s−1]) = 39.1 and 40.4. Our results support the presence of an AGN in these two galaxies and an ultraluminous X-ray source (ULX) in one of them. For the AGNs, we estimate BH masses of M BH ∼ 105−6 M ⊙ and Eddington ratios on the order of ∼10−3.

Stripe 82-XL: The ∼54.8 deg2 and ∼18.8 Ms Chandra and XMM-Newton Point-source Catalog and Number of Counts

We present an enhanced version of the publicly available Stripe 82X catalog (S82-XL), featuring a comprehensive set of 22,737 unique X-ray point sources identified with a significance ≳4σ. This catalog is four times larger than the original Stripe 82X catalog, by including additional archival data from the Chandra and XMM-Newton telescopes. Now covering ∼54.8 deg2 of nonoverlapping sky area, the S82-XL catalog roughly doubles the area and depth of the original catalog, with limiting fluxes (half-area fluxes) of 3.4 × 10−16 (2.4 × 10−15), 2.9 × 10−15 (1.5 × 10−14), and 1.4 × 10−15 (9.5 × 10−15) erg s−1 cm−2 across the soft (0.5–2 keV), hard (2–10 keV), and full (0.5–10 keV) bands, respectively. S82-XL occupies a unique region of flux-area parameter space compared to other X-ray surveys, identifying sources with rest-frame luminosities from 1.2 × 1038 to 1.6 × 1047 erg s−1 in the 2–10 keV band (median X-ray luminosity, 7.2 × 1043 erg s−1), and spectroscopic redshifts up to z ∼ 6. By using hardness ratios, we derived the obscuration of active galactic nuclei (AGNs), obtaining a median value of log(NH/cm−2)=21.6−1.6+1.0 and an overall, obscured fraction ( log(NH/cm−2)>22 ) of ∼36.9%. S82-XL serves as a benchmark in X-ray surveys and, with its extensive multiwavelength data, is especially valuable for comprehensive studies of luminous AGNs.

The hot circumgalactic medium in the eROSITA All-Sky Survey

Context. The circumgalactic medium (CGM) provides the material needed for galaxy formation and influences galaxy evolution. The hot (T > 106K) CGM is poorly detected around galaxies with stellar masses (M*) lower than 3 × 1011 M⊙ due to the low surface brightness. Aims. We aim to detect the X-ray emission from the hot CGM around Milky Way-mass (MW-mass, log(M*/M⊙) = 10.5 − 11.0) and M31-mass (log(M*/M⊙) = 11.0 − 11.25) galaxies, in addition to measuring the X-ray surface brightness profile of the hot CGM. Methods. We applied a stacking technique to gain enough statistics to detect the hot CGM. We used the X-ray data from the first four SRG/eROSITA All-Sky Surveys (eRASS:4). We discussed how the satellite galaxies could bias the stacking and the method we used to carefully build the central galaxy samples. Based on the SDSS spectroscopic survey and halo-based group finder algorithm, we selected central galaxies with spectroscopic redshifts of zspec < 0.2 and stellar masses of 10.0 < log(M*/M⊙) < 11.5 (85 222 galaxies) – or halo masses of 11.5 < log(M200m/M⊙) < 14.0 (125,512 galaxies). By stacking the X-ray emission around galaxies, we obtained the mean X-ray surface brightness profiles. We masked the detected X-ray point sources and carefully modeled the X-ray emission from the unresolved active galactic nuclei (AGN) and X-ray binaries (XRB) to obtain the X-ray emission from the hot CGM. Results. We measured the X-ray surface brightness profiles for central galaxies of log(M*/M⊙) > 10.0 or log(M200m/M⊙) > 11.5. We detected the X-ray emission around MW-mass and more massive central galaxies extending up to the virial radius (Rvir). The signal-to-noise ratio (S/N) of the extended emission around MW-mass (M31-mass) galaxy is about 3.1σ (4.7σ) within Rvir. We used a β model to describe the X-ray surface brightness profile of the hot CGM (SX, CGM). We obtained a central surface brightness of log(SX,0[erg s−1 kpc−2]) = 36.7−0.4+1.4 (37.1−0.4+1.5) and β = 0.43−0.06+0.10 (0.37−0.02+0.04) for MW-mass (M31-mass) galaxies. For galaxies with log(M200m/M⊙) > 12.5, the extended X-ray emission is detected with S/N > 2.8σ and the SX, CGM can be described by a β model with β ≈ 0.4 and log(SX,0[erg s−1 kpc−2]) > 37.2. We estimated the baryon budget of the hot CGM and obtained a value that is lower than the prediction of ΛCDM cosmology, indicating significant gas depletion in these halos. We extrapolated the hot CGM profile measured within Rvir to larger radii and found that within ≈3Rvir, the baryon budget is close to the ΛCDM cosmology prediction. Conclusions. We measured the extended X-ray emission from representative populations of central galaxies around and above MW-mass out to Rvir. Our results set a firm footing for the presence of the hot CGM around such galaxies. These measurements constitute a new benchmark for galaxy evolution models and possible implementations of feedback processes therein.

Searching for the Highest-z Dual Active Galactic Nuclei in the Deepest Chandra Surveys

We present an analysis searching for dual active galactic nuclei (AGN) among 62 high-redshift (2.5 < z < 3.5) X-ray sources selected from the X-UDS, AEGIS-XD, CDF-S, and COSMOS-Legacy Chandra surveys. We aim to quantify the frequency of dual AGN in the high-redshift Universe, which holds implications for black hole merger timescales and low-frequency gravitational wave detection rates. We analyze each X-ray source using BAYMAX, an analysis tool that calculates the Bayes factor for whether a given archival Chandra AGN is more likely a single or dual point source. We find no strong evidence for dual AGN in any individual source in our sample. We increase our sensitivity to search for dual AGN across the sample by comparing our measured distribution of Bayes factors to that expected from a sample composed entirely of single point sources and find no evidence for dual AGN in the sample distribution. Although our analysis utilizes one of the largest Chandra catalogs of high-z X-ray point sources available to study, the findings remain limited by the modest number of sources observed at the highest spatial resolution with Chandra and the typical count rates of the detected sources. Our nondetection allows us to place an upper limit on the X-ray dual AGN fraction at 2.5 < z < 3.5 of 4.8% at the 95% confidence level. Expanding substantially on these results at X-ray wavelengths will require future surveys spanning larger sky areas and extending to fainter fluxes than has been possible with Chandra. We illustrate the potential of the AXIS mission concept in this regard.

Flaring Stars in a Nontargeted Millimeter-wave Survey with SPT-3G

We present a flare star catalog from 4 yr of nontargeted millimeter-wave survey data from the South Pole Telescope (SPT). The data were taken with the SPT-3G camera and cover a 1500 deg2 region of the sky from 20h40m0s to 3h20m0s in right ascension and from −42° to −70° in declination. This region was observed on a nearly daily cadence from 2019 to 2022 and chosen to avoid the plane of the galaxy. A short-duration transient search of this survey yields 111 flaring events from 66 stars, increasing the number of both flaring events and detected flare stars by an order of magnitude from the previous SPT-3G data release. We provide cross-matching to Gaia DR3, as well as matches to X-ray point sources found in the second ROSAT all-sky survey. We have detected flaring stars across the main sequence, from early-type A stars to M dwarfs, as well as a large population of evolved stars. These stars are mostly nearby, spanning 10–1000 pc in distance. Most of the flare spectral indices are constant or gently rising as a function of frequency at 95/150/220 GHz. The timescale of these events can range from minutes to hours, and the peak ν L ν luminosities range from 1027 to 1031 erg s−1 in the SPT-3G frequency bands.

Characterisation of the X-ray point source variability in the eROSITA south ecliptic pole field

Aims.During the Spectrum Roentgen Gamma (SRG)/eROSITA all-sky surveys, X-ray sources close to the South Ecliptic Pole (SEP) are observed almost every 4 h. We aim to identify the sources exhibiting the most significant long-term X-ray variability within 3° of the SEP in the first three surveys, and investigate their properties.Methods.We determined the variability significance of ~104sources observed by eROSITA within 3° of the SEP by using thresholds on the Bayesian excess variance (SCATT_LO) and the maximum amplitude deviation (AMPL_SIG). Sources exhibiting a variability significance above 3σwere subdivided into likely Galactic and extragalactic sources, by using spectral and photometric information of their optical counterparts. We quantified the X-ray normalised excess variances of all variable sources, and also calculated the periodograms of the brightest ones.Results.Out of more than 104X-ray sources detected by eROSITA within 3° of the SEP, we identified 453 that exhibit significant X-ray variability. SCATT_LO is significantly more sensitive to detecting variable sources in this field, but AMPL_SIG helps to provide a more complete variability sample. Of those variable sources, 168 were classified as likely extragalactic, and 235 as likely Galactic. The periodograms of most bright and variable extragalactic sources are approximately described by an aliased power law (P∞ν−α) with an index ofα≈ 1. We identified a potential tidal disruption event, and long-term transient sources. The stellar X-ray variability was predominantly caused by bright X-ray flares from coronally active stars.

Periodicity from X-ray sources within the inner Galactic disk

Aims. For many years it had been claimed that the Galactic ridge X-ray emission at the Galactic Center (GC) is truly diffuse in nature. However, with the advancement of modern X-ray satellites, it has been found that most of the diffuse emission actually comprises thousands of previously unresolved X-ray point sources. Furthermore, many studies suggest that a vast majority of these X-ray point sources are magnetic cataclysmic variables (CVs) and active binaries. One unambiguous way to identify these magnetic CVs and other sources is by detecting their X-ray periodicity. Therefore, we systematically searched for periodic X-ray sources in the inner Galactic disk, including the GC region. Methods. We used data from our ongoing XMM-Newton Heritage Survey of the inner Galactic disk (350° ≲l ≲ +7° and −1° ≲b ≲ +1°) plus archival XMM-Newton observations of the GC. We computed the Lomb-Scargle periodogram for the soft (0.2–2 keV), hard (2–10 keV), and total (0.2–10 keV) band light curves to search for periodicities. Furthermore, we modeled the power spectrum using a power-law model to simulate 1000 artificial light curves and estimate the detection significance of the periodicity. We fitted the energy spectra of the sources using a simple power-law model plus three Gaussians, at 6.4, 6.7, and 6.9 keV, for the iron K emission complex. Results. We detected periodicity in 26 sources. For 14 of them, this is the first discovery of periodicity. For the other 12 sources, we found periods similar to those already known, indicating no significant period evolution. The intermediate polar (IP) type sources display relatively hard spectra compared to polars. We also searched for the Gaia counterparts of the periodic sources to estimate their distances using the Gaia parallax. We found a likely Gaia counterpart for seven sources. Conclusions. Based on the periodicity, hardness ratio, and the equivalent width of Fe K line emission, we have classified the sources into four categories: IPs, polars, neutron star X-ray binaries, and unknown. Of the 14 sources for which we detect the periodicity for the first time, four are likely IPs, five are likely polars, two are neutron star X-ray binaries, and three are of an unknown nature.

Uncovering an Excess of X-Ray Point Sources in the Halos of Virgo Late-type Galaxies

We present a systematic search for extraplanar X-ray point sources around 19 late-type, highly inclined disk galaxies residing in the Virgo cluster, based on archival Chandra observations reaching a source detection sensitivity of L(0.5–8 keV) ∼ 1038 erg s−1. Based on the cumulative source surface density distribution as a function of projected vertical distance from the disk midplane, we identify a statistically significant (∼3.3σ) excess of ∼20 X-ray sources within a projected vertical off-disk distance of 0.′92–2.′5 (∼4.4–12 kpc), the presence of which cannot be explained by the bulk stellar content of the individual galaxies, nor by the cosmic X-ray background. On the other hand, there is no significant evidence for an excess of extraplanar X-ray sources in a comparison sample of field late-type edge-on galaxies, for which Chandra observations reaching a similar source detection sensitivity are available. We discuss the possible origins for the observed excess, including low-mass X-ray binaries (LMXBs) associated with globular clusters, supernova-kicked LMXBs, and high-mass X-ray binaries born in recent star formation induced by ram pressure stripping of the disk gas, as well as a class of intracluster X-ray sources previously identified around early-type member galaxies of Virgo. We find that none of these X-ray populations can naturally dominate the observed extraplanar excess, although supernova-kicked LMXBs and the effect of ram pressure are most likely relevant.

The X-ray binaries in M83: Will any of them form gravitational wave sources for LIGO-VIRGO-KAGRA?

There are 214 X-ray point sources (LX &gt; 1035 erg s−1) identified as X-ray binaries (XRBs) in the nearby spiral galaxy M83. Since XRBs are powered by accretion onto a neutron star (NS) or a black hole (BH) from a companion or donor star, these systems are promising progenitors of merging double compact objects (DCOs): BH-BH, BH-NS, or NS-NS systems. The connection (i.e., XRBs evolving into DCOs) may provide some hints to the as-yet-unanswered question: what is the origin of the LIGO, Virgo, and KAGRA mergers? Available observations do not allow us to determine what the final fate of the XRBs observed in M83 will be. However, we can use an evolutionary model of isolated binaries to reproduce the population of XRBs in M83 by matching model XRB numbers, types, and luminosities to observations. Knowing the detailed properties of M83 model XRBs (donor and accretor masses, and their evolutionary ages and orbits), we follow their evolution to the deaths of donor stars to check whether any merging DCOs are formed. Although all merging DCOs in our isolated binary evolution model go through the XRB phase (defined as reaching X-ray luminosity from RLOF or wind accretion onto NSs or BHs above 1035 erg s−1), only very few XRBs evolve to form merging (in Hubble time) DCOs. For M83, with its solar-like metallicity stars and continuous star formation, we find that only ∼1 − 2% of model XRBs evolve into merging DCOs depending on the adopted evolutionary physics. This is caused by (i) the merger of the donor star with a compact object during the common envelope phase, (ii) a binary disruption at the supernova explosion of a donor star, (iii) the formation of a DCO on a wide orbit (merger time longer than Hubble time).

Discovery and timing of pulsar J2016+3711 in supernova remnant CTB 87 with FAST

ABSTRACT We report on our discovery of the radio pulsar, PSR J2016+3711, in supernova remnant (SNR) CTB 87, with a ∼10.8σ significance of pulses, which confirms the compact nature of the X-ray point source in CTB 87. It is the first pulsar discovered in SNRs using Five-hundred-meter Aperture Spherical radio Telescope (FAST). Its integrated radio pulse profile can be well described by a single component, with a width at 50 per cent of the peak flux density of about 28.1○ and an effective width of about 32.2○. The mean flux density at 1.25 GHz is estimated to be about 15.5 $\mu$Jy. Combined with the non-detection of the radio pulse at lower frequencies, the radio spectral index of the pulsar is constrained to be ≲2.3. We also present the timing solution based on 28 follow-up FAST observations. Our results reveal a period of 50.81 ms, period derivative of 7.2 × 10−14 s s−1, and dispersion measure of 428 pc cm−3. The strength of the equatorial surface magnetic dipole magnetic field is inferred to be about 1.9 × 1012 G. Using the ephemeris obtained from the radio observations, we searched Fermi-LAT data for gamma-ray pulsations but detected no pulsed signal. We also searched for radio pulses with FAST towards the X-ray counterpart of the gamma-ray binary HESS J1832−093 proximate to SNR G22.7−00.2 but found no signal.

The high energy X-ray probe (HEX-P): Resolving the nature of Sgr A* flares, compact object binaries and diffuse X-ray emission in the Galactic center and beyond

HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (&lt;10″ FWHM) and broad spectral coverage (0.2–80 keV) with an effective area far superior to current facilities’ (including XMM-Newton and NuSTAR). These capabilities will enable revolutionary new insights into a variety of important astrophysical problems. We present scientific objectives and simulations of HEX-P observations of the Galactic Center (GC) and Bulge. We demonstrate the unique and powerful capabilities of the HEX-P observatory for studying both X-ray point sources and diffuse X-ray emission. HEX-P will be uniquely equipped to explore a variety of major topics in Galactic astrophysics, allowing us to 1) investigate broad-band properties of X-ray flares emitted from the supermassive black hole (BH) at Sgr A* and probe the associated particle acceleration and emission mechanisms; 2) identify hard X-ray sources detected by NuSTAR and determine X-ray point source populations in different regions and luminosity ranges; 3) determine the distribution of compact object binaries in the nuclear star cluster and the composition of the Galactic Ridge X-ray emission; 4) identify X-ray transients and measure fundamental parameters such as black hole spin; 5) find hidden pulsars in the Galactic Center; 6) search for BH–OB binaries and hard X-ray flares from young stellar objects in young massive clusters; 7) measure white dwarf (WD) masses of magnetic CVs to deepen our understanding of CV evolution and the origin of white dwarf magnetic fields; 8) explore primary particle accelerators in the GC in synergy with future TeV and neutrino observatories; 9) map out cosmic-ray distributions by observing non-thermal X-ray filaments; 10) explore past X-ray outbursts from Sgr A* through X-ray reflection components from giant molecular clouds.

SRGz: Classification of eROSITA Point X-ray Sources in the 1$${\%}$$DESI Region and Calibration of Photometric Redshifts*

SRGz: Classification of eROSITA Point X-ray Sources in the 1$${\%}$$DESI Region and Calibration of Photometric Redshifts*

The Chandra Cygnus OB2 Legacy Survey: Design and X-Ray Point-source Catalog

The Cygnus OB2 association is the largest concentration of young and massive stars within 2 kpc of the Sun, including an estimated ∼65 O-type stars and hundreds of OB stars. The Chandra Cygnus OB2 Legacy Survey is a large imaging program undertaken with the Advanced CCD Imaging Spectrometer on board the Chandra X-ray Observatory. The survey has imaged the central 0.5 deg2 of the Cyg OB2 association with an effective exposure of ∼120 ks and an outer 0.35 deg2 area with an exposure of ∼60 ks. Here we describe the survey design and observations, discuss the data reduction and source detection, and present a catalog of ∼8000 X-ray point sources. The survey design employs a grid of 36 heavily (∼50%) overlapping pointings, a method that overcomes Chandra's low off-axis sensitivity and produces a highly uniform exposure over the inner 0.5 deg2. The full X-ray catalog is described here and is made available online.

Chandra Observation of NGC 1559: Eight Ultraluminous X-Ray Sources Including a Compact Binary Candidate

Despite the 30 yr history of ultraluminous X-ray sources (ULXs) studies, issues such as the majority of their physical natures (i.e., neutron stars, stellar-mass black holes, or intermediate black holes) as well as the accretion mechanisms are still under debate. Expanding the ULX sample size in the literature is clearly a way to help. To this end, we investigated the X-ray source population, ULXs in particular, in the barred spiral galaxy NGC 1559 using a Chandra observation made in 2016. In this 45 ks exposure, 33 X-ray point sources were detected within the 2.′7 isophotal radius of the galaxy. Among them, eight ULXs were identified with the criterion of the X-ray luminosity L x > 1039 erg s−1 (0.3–7 keV). Both X-ray light curves and spectra of all the sources were examined. Except for some low-count spectra that only provide ambiguous spectral fitting results, all the X-ray sources were basically spectrally hard and therefore likely have nonthermal origins. While no strong X-ray variability was present in most of the sources owing to the relatively short exposure of the observation, we found an intriguing ULX, named X-24, exhibiting a periodicity of ∼7500 s with a detection significance of 2.7σ. We speculate that it is the orbital period of the system. Roche-lobe overflow and Roche limit are consistent with the speculation. Thus, we suggest that X-24 may be one of the rare compact binary ULXs, and hence, a good candidate as a stellar-mass black hole.

X-Ray Properties of Optically Variable Low-mass AGN Candidates

We present an X-ray analysis of 14 nearby (z < 0.044) active galactic nuclei (AGNs) in low-mass galaxies (M * ≲ 5 × 109 M ⊙) selected based on their optical variability. Comparing and contrasting different AGN selection techniques in low-mass galaxies is essential for obtaining an accurate estimate of the active fraction in this regime. We use both new and archival observations from the Chandra X-ray Observatory to search for X-ray point sources consistent with AGNs. Four objects have detected nuclear X-ray emission with luminosities ranging from L 0.5−7 ≈ 3 × 1040 to 9 × 1042 erg s−1 with two more marginal detections. All of the detected galaxies have luminosities exceeding those anticipated from X-ray binaries, and all sources are nuclear, suggesting the X-ray emission in most sources is due to an AGN. These observations demonstrate the success of variability at identifying AGNs in low-mass galaxies. We also explore emission-line diagnostics and discuss the differences in the results of these methods for AGN selection, in particular regarding low-mass and low-metallicity systems.

Multiwavelength Characterization of the High-mass X-Ray Binary Population of M33

We present multiwavelength characterization of 65 high-mass X-ray binary (HMXB) candidates in M33. We use the Chandra ACIS survey of M33 (ChASeM33) catalog to select hard X-ray point sources that are spatially coincident with UV-bright point-source optical counterparts in the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region catalog, which covers the inner disk of M33 at near-IR, optical, and near-UV wavelengths. We perform spectral energy distribution fitting on multiband photometry for each point-source optical counterpart to measure its physical properties including mass, temperature, luminosity, and radius. We find that the majority of the HMXB companion star candidates are likely B-type main-sequence stars, suggesting that the HMXB population of M33 is dominated by Be X-ray binaries (Be-XRBs), as is seen in other Local Group galaxies. We use spatially resolved recent star formation history maps of M33 to measure the age distribution of the HMXB candidate sample and the HMXB production rate for M33. We find a bimodal distribution for the HMXB production rate over the last 80 Myr, with a peak at ∼10 and ∼40 Myr, which match theoretical formation timescales for the most massive HMXBs and Be-XRBs, respectively. We measure an HMXB production rate of 107–136 HMXBs/(M ⊙ yr−1) over the last 50 Myr and 150–199 HMXBs/(M ⊙ yr−1) over the last 80 Myr. For sources with compact object classifications from overlapping NuSTAR observations, we find a preference for giant/supergiant companion stars in black hole HMXBs and main-sequence companion stars in neutron star HMXBs.

The X-ray point source population hosted by globular clusters in the elliptical galaxy NGC 4261

ABSTRACT Utilizing archival Chandra X-ray Observatory data and Hubble Space Telescope globular cluster catalogues, we probe the time-domain properties of the low mass X-ray binary population in the elliptical galaxy NGC 4261. Of the 98 unique X-ray sources identified in this study, 62 sources are within the optical field of view and, of those, 33 per cent are aligned with an optical cluster counterpart. We find twenty X-ray sources coincident with globular clusters; two are previously discovered ultra-luminous X-ray sources (ULXs) and eighteen are low mass X-ray binaries (GCLMXBs) with LX &amp;lt; 1039 erg s−1. ULXs are a heterogeneous class of extremely bright X-ray binaries (LX &amp;gt; 1039 erg s−1) and ULXs located in globular clusters (GCULXs) and may be indicators of black holes. Identifying these unusually X-ray bright sources and measuring their optical properties can provide valuable constraints on the progenitors of gravitational wave sources. We compare observations of these sources to the twenty previously studied GCULXs from five other early-type galaxies, and find that GCULXs in NGC 4261 are of similar colour and luminosity and do not significantly deviate from the rest of the sample in terms of distance from the galaxy centre or X-ray luminosity. Both the GCULX and GCLMXB populations of NGC 4261 show long-term variability; the former may have implications for fast radio bursts originating in globular clusters and the latter will likely introduce additional scatter into the low mass end of GCLMXB X-ray luminosity functions.

SRGz: Machine Learning Methods and Properties of the Catalog of SRG/eROSITA Point X-ray Source Optical Counterparts in the DESI Legacy Imaging Surveys Footprint

SRGz: Machine Learning Methods and Properties of the Catalog of SRG/eROSITA Point X-ray Source Optical Counterparts in the DESI Legacy Imaging Surveys Footprint