TITLE: GCN CIRCULAR NUMBER: 21492 SUBJECT: GRB 170810A: VLA Detection DATE: 17/08/16 00:22:47 GMT FROM: Kate Alexander at Harvard K. D. Alexander (Harvard), T. Laskar (NRAO / UC Berkeley), and E. Berger (Harvard) report on behalf of a larger collaboration: We observed the Swift GRB 170810A (Gibson et al., GCN 21450) at multiple frequencies with the Karl G. Jansky Very Large Array (VLA) beginning 2017 August 12.77 UT (1.85 days after the burst). At a mean frequency of 7.1 GHz, we detect a radio source with a preliminary flux density of ~0.1 mJy. In follow-up observations on 2017 August 15.03 UT the source had faded to ~half its original brightness, confirming this as the radio afterglow of GRB 170810A. The best-fit radio position is RA (J2000) = 12:31:45.346 Dec (J2000) = +03:39:38.61 with an uncertainty of 0.4” in each coordinate. This is consistent with the refined Swift/XRT position (Goad et al. GCN 21451) and the position of the Swift/UVOT afterglow (LaPorte et al. GCN 21454). We thank the VLA staff for rapidly executing these observations.