An expanded ultraluminous X-ray source catalogue

Abstract

Context. Ultraluminous X-ray sources (L X ×10 39 erg s −1 , ULXs) are excellent probes for extreme accretion physics, star formation history in galaxies, and intermediate-mass black holes searches. As the sample size of X-ray data from modern observatories such as XMM-Newton and Chandra increases, producing extensive catalogues of ULXs and studying their collective properties has become both a possibility and a priority. Aims. Our aim is to build a clean updated ULX catalogue based on one of the most recent XMM-Newton X-ray serendipitous survey data releases, 4XMM-DR9, and the most recent and exhaustive catalogue of nearby galaxies, HECATE. We performed a preliminary population study to test if the properties of the expanded XMM-Newton ULX population are consistent with previous findings. Methods. We performed positional cross-matches between XMM-Newton sources and HECATE objects to identify host galaxies, and we used distance and luminosity arguments to identify ULX candidates. We flagged interlopers by finding known counterparts in external catalogues and databases such as Gaia DR2, SSDS, Pan-STARRS1, the NASA/IPAC Extragalactic Database, and SIMBAD. Source, galaxy and variability parameters from 4XMM-DR9, HECATE, and 4XMM-DR9s were used to study the spectral, abundance, and variability properties of the ULX sample. Results. We identify 779 ULX candidates, 94 of which hold L X 5 × 10 40 erg s −1 . Spiral galaxies are more likely to host ULXs. For early spiral galaxies the number of ULX candidates per star-forming rate is consistent with previous studies, while a significant ULX population in elliptical and lenticular galaxies also exists. Candidates hosted by late-type galaxies tend to present harder spectra and to undergo more extreme inter-observation variability than those hosted by early-type galaxies. Approximately 30 candidates with L X > 10 41 erg s −1 are also identified, constituting the most interesting candidates for intermediate-mass black hole searches. Conclusions. We have built the largest ULX catalogue to date. Our results on the spectral and abundance properties of ULXs confirm the findings made by previous studies based on XMM-Newton and Chandra data, while our population-scale study on variability properties is unprecedented. Our study, however, provides limited insight into the properties of the brightest ULX candidates due to the small sample size. The expected growth of X-ray catalogues and potential future follow-ups will aid in drawing a clearer picture.

Digging a little deeper: characterizing three new extreme ULX candidates

“…The presence of a Galactic contaminant highlights a weakness in the filtering of W22 for such objects. However, this could readily be corrected by the use of Gaia data and/or the use of statistical/multiwavelength identification techniques to better identify foreground objects in future catalogues, as has already been done in the work of Bernadich et al (2022) andTranin et al (2023). 4XMM J091948.8-121429 on the other hand remains an excellent eULX candidate, but suffers from minimal archival data being available at present, so also requires further observational study to improve our understanding of it.…”

“…This example shows that more filtering is required to pick up Galactic objects, for example looking for counterparts with measured parallax at low Galactic latitudes. The 4XMM-DR9 ULX catalogue of Bernadich et al (2022) performs better than W22 in this regard by searching catalogues including Gaia DR2 for optical point source counterparts to its ULX candidates, and then using the X-ray/optical flux ratios to exclude stars and other objects. The even more recent catalogue of Tranin et al (2023) uses an automated probabilistic classification of X-ray sources to produce a catalogue with a claimed contamination of only 2%.…”

Multiwavelength Constraints on the Origin of a Nearby Repeating Fast Radio Burst Source in a Globular Cluster

“…The histogram of persistent X-ray luminosities for ULX sources was calculated using values from the ULX source catalog available in ref. [143]. We adopt a typical luminosity definition of L X ≥ 10 39 erg s -1 for ULX sources.…”

Long-term X-ray/UV variability in ULXs

“…The Neil Gehrels Swift Observatory (Swift) (Gehrels et al 2004) is capable of observing simultaneously in both the UV and X-ray bands via its UVOT (Roming et al 2005) and XRT (Burrows et al 2005) cameras, and so provides a unique opportunity to explore whether observations of ULXs are consistent with any of the predictions discussed above. We begin by creating our ULX sample by crossmatching several ULX catalogues, (Earnshaw et al 2019;Kovlakas et al 2020;Bernadich et al 2022;Walton et al 2022) with the Swift Master Catalogue (SWIFTMASTR), accessible via HEASARC 1 . For the sake of comparison to nearby sources where data quality is high, we also include three extensively studied Galactic sources which reach super-Eddington rates of accretion, Swift J0243.6+6124, SS433 and V404 Cygni.…”