Zhao, Yue, Gandhi, Poshak, Knigge, Christian, Charles, Phil, Stern, Daniel, Boorman, Peter, Nuchvanichakul, Pornisara, Brown, Cordelia Dashwood and Buckley, David A.H. (2026) A comprehensive search for high-velocity X-ray sources: new compact object binary candidates in the Gaia era. Mon Not R Astron Soc, 546 (4), [stag058]. (doi:10.1093/mnras/stag058).
Abstract
We perform a comprehensive search for high-velocity X-ray sources with large X-ray/optical flux ratios ( F X /F G ), 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, parallax es, and proper motions, we compute peculiar velocities ( υpec ) relative t o Galactic disc rotation. Remaining agnostic about radial velocities (RVs), we vary RVs to find the minimum possible υpec values ( υpec , min ). Uncertainties on υpec , min are estimated via Monte Carlo resampling, and we select X-ray sources that have 1 σ low er limits on υpec , min ≥ 200 km s −1 and high F X /F G 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 υpec could serve as an effective indicator for the presence of a neutron star or black hole companion. Our selection yields a sample of 2372 sources, from which we construct a gold sample of 7 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.
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