TITLE: GCN CIRCULAR NUMBER: 30477 SUBJECT: GRB 210702A: ATCA detection of radio rebrightening DATE: 21/07/22 22:42:20 GMT FROM: Tanmoy Laskar at U of Bath T. Laskar (U. of Bath) and S. Bhandari (CSIRO) report on behalf of a larger collaboration: "Following the initial detection of the radio counterpart of GRB 210702A (Lien et al., GCN 30351) with the Australia Telescope Compact Array (ATCA) on 2021 July 06, 3.50 days after the burst (Laskar et al., GCN 30424), we have been monitoring this source with ATCA at 5.5, 9.0, 16.7, 21.2, and 34 GHz. The 34 GHz radio counterpart was observed to fade, until observations taken on 2021 July 13 indicated a non-detection with map rms ~ 60 uJy at a mid-time of 10.3 days after the burst. We observed GRB 210702A with ATCA again at the above frequencies beginning on 2021 July 21 07:00 UTC with the array in a hybrid (H168) configuration. Preliminary analysis reveals a strong (> 10 sigma) detection at 34 GHz with a flux density of ~ 0.7 mJy at a mid-time of 18.5 days after the burst, implying a significant rebrightening of the radio afterglow. Similar rebrightening is observed at 21.2 and 16.7 GHz. Detailed analysis is ongoing and further observations are planned. We thank the CSIRO staff for approving and scheduling these observations. The Australia Telescope Compact Array is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site."