A comprehensive search for high-velocity X-ray sources: new compact object binary candidates in the Gaia era

Journal article

We perform a comprehensive search for high-velocity X-ray sources with large X-ray/optical flux ratios (), identifying candidates for interacting black hole or neutron star binaries potentially accelerated by supernova natal kicks. We cross-match X-ray points sources from a variety of catalogues (Chandra, XMM–Newton, Swift, and eROSITA) with Gaia DR3. Using Gaia coordinates, parallaxes, and proper motions, we compute peculiar velocities () relative to Galactic disc rotation. Remaining agnostic about radial velocities (RVs), we vary RVs to find the minimum possible values (). Uncertainties on are estimated via Monte Carlo resampling, and we select X-ray sources that have lower limits on and high values. We show that this velocity threshold excludes most contaminants (e.g. cataclysmic variables and active binaries) while retaining a sensible fraction of compact object binaries, demonstrating that could serve as an effective indicator for the presence of a neutron star or black hole companion. Our selection yields a sample of sources, from which we construct a gold sample of sources that have relatively well-constrained astrometry and confident optical counterparts. Follow-up is necessary to confirm and characterise their high-energy emission, as well as a Galactic disc vs. halo origin.

Authors: Zhao, Y; Gandhi, P; Knigge, C; Charles, P; Stern, D

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Oxford University Press
• Journal: Monthly Notices of the Royal Astronomical Society
• Volume: 546
• Issue: 4
• Article number: stag058
• Publication date: 2026-01-10
• Acceptance date: 2026-01-07
• DOI: 10.1093/mnras/stag058
• EISSN: 1365-2966
• ISSN: 0035-8711
• Language: English
• Keywords: binary: close; supernova: general; stars: black hole; stars: neutron; X-rays: binaries