GCN Circular 39699
Tao An, Yuanqi Liu (SHAO, China), Jinjun Geng, Xuefeng Wu (PMO, China), Ailing Wang (IHEP, China) report on behalf of a large collaboration.
We report the detection of a radio counterpart to GRB 250309B-AT2025dws (GCN 39629, 39637, 39639) with the Australia Telescope Compact Array (ATCA).
We conducted ATCA observations at 5.5 and 9 GHz on UT14:00-20:59 March 10, 2025 (~T0+1 day) targeting both the optical counterpart position of GRB 250309B-AT2025dws (GCN 39639) and a reported possible neutrino event position XRT1 (GCN 39631, 39633). No significant radio emission was detected above our 5σ detection threshold at either position, with a 1σ sensitivity of approximately 30 μJy/beam.
Subsequent ATCA observations on UT14:00-20:59 March 12, 2025 (~T0+3 days) revealed a clear detection of radio emission at the position of GRB 250309B-AT2025dws with 0.322 ± 0.009 mJy at 5.5 GHz.
The detection of this relatively bright radio afterglow (comparable to some of the brighter GRB radio afterglows) provides an excellent opportunity for continued monitoring of the spectral and temporal evolution of the afterglow emission. We plan to continue monitoring this source with ATCA.
We thank the Jamie Stevens for rapid response in scheduling these observations.
We thank the CSIRO Space and Astronomy staff for supporting 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.