VLBA astrometry combined with Gaia DR1 epoch

But as has been suggested by numerous investigators, astrometry offers an additional path to gravitational wave detection. Gravitational waves deflect light rays of extragalactic objects, creating apparent proper motions in a quadrupolar (and higher-order modes) pattern.

Astrometry of extragalactic radio sources is sensitive to gravitational waves with frequencies between roughly 10^-18^ and 10^-8^Hz (H_0_ and 1/3yr^-1^), overlapping and bridging the pulsar timing and CMB polarization regimes. We present a methodology for astrometric gravitational wave detection in the presence of large intrinsic uncorrelated proper motions (i.e., radio jets). We obtain 95% confidence limits on the stochastic gravitational wave background using 711 radio sources, {Omega}_GW_<0.0064, and using 508 radio sources combined with the first Gaia data release: {Omega}_GW_<0.011.