High-velocity X-ray sources

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 (vpec) relative to Galactic disc rotation.

Remaining agnostic about radial velocities (RVs), we vary RVs to find the minimum possible vpec values (vpec_min_). Uncertainties on vpec_min_ are estimated via Monte Carlo resampling, and we select X-ray sources that have 1 sigma lower limits on vpec_min_>=200km/s 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 vpec could serve as an effective indicator for the presence of a neutron star or black hole companion.