GCN Circular 45704
ATCA observations of GRB 260909A
From: Lauren Rhodes at McGill
Issued: 2026-09-23 14:06 UTC
Type: GRB, Radio Transient
Why this event is posted: it has drawn 17 GCN Circulars, at or above the top-10% threshold of 14.

L. Rhodes (TSI/McGill), G. E. Anderson (CSIRO), A. J. van der Horst (GWU), J. K. Leung (UofT/HUJI), S. Chastain (TTU), A. Gulati (Utah), J. Chauhan (ULeicester) on behalf of the PanRadio GRB collaboration

We observed GRB 260909A (Saccardi et al., GCN 45534) starting at 18-Sep-2026 14:56UT for 4 hours with the Australia Telescope Compact Array (ATCA), as part of the "PanRadio GRB" Large ATCA follow-up programme C3542 (PI. Anderson).

We report a preliminary detection of a radio counterpart at coordinates consistent with those reported in de Ugarte Postigo et al., (GCN 45597):
7.2GHz 59+/-9uJy
9.1GHz 62+/-8uJy
11.0GHz 86+/-9uJy

The positive spectral index indicates that the spectral peak of the afterglow is above the ATCA observing band. More observations are ongoing.

We thank the CSIRO Space and Astronomy staff for supporting these observations.
We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (Research Organization Registry (ROR) Search (ror.org)) which is funded by the Australian Government for operation as a National Facility managed by CSIRO.

Filter: gamma-ray bursts are posted only if in the top 10% of the past year's — by fluence (total energy received per cm², from Fermi GBM, Konus-Wind, GECAM and similar circulars; now ≥ 3.9×10^-5 erg/cm²) or by the number of GCN Circulars about the burst (now ≥ 14). Thresholds are recalculated monthly.
Relayed automatically from NASA's General Coordinates Network.