Validating the bright Gaia celestial reference frame with new VLBI astrometry of radio stars

Aims. There exist inconsistencies between the bright and faint Gaia Celestial Reference Frame 3 (Gaia-CRF3), which manifests as a systematic rotation and needs to be independently estimated then corrected in future data releases.Methods. We collected 64 radio stars with very long baseline interferometry (VLBI) astrometry, of which 16 have new VLBI observations with reference epochs close to Gaia. We estimated the orientation and spin biases of the bright Gaia-CRF3 by comparing VLBI radio star astrometry with their Gaia DR3 counterparts. We also attempted to estimate orientation by utilizing the a priori magnitude-dependent spin parameters derived from Gaia’s internal estimations.Results. Our independent estimation of the orientation at G < 10.5 is [−15 ± 119, +330 ± 139, +218 ± 109] μas (J2016.0), and the spin ([+21 ± 18, +52 ± 20, −7 ± 20] μ μas yr^{−1) agrees with Gaia’s internal estimation within a 1σ range. The orientation-only estimation suggests that the orientation bias of the bright Gaia-CRF3 may also be magnitude-dependent.}