[vsnet-grb-info 28374] GRB 210702A: ATCA detection of radio rebrightening

[GCN Circulars]

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  <tanmoylaskar at gmail.com>

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."