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

Abstract: 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. We collected 64 radio stars with 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 internal estimation. Our independent estimation of the orientation at G<10.5 is [-15\pm119, +330\pm139,+218\pm109] uas (J2016.0), and the spin ([+21\pm18, +52\pm20,-7\pm20] uas/yr) agrees with Gaia internal estimation within 1-sigma range. The orientation-only estimation suggests that the orientation bias of the bright Gaia-CRF3 may also be magnitude-dependent.