[vsnet-grb-info 28555] GRB 210726A: VLA radio afterglow detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30658
SUBJECT: GRB 210726A: VLA radio afterglow detection
DATE:    21/08/18 20:48:40 GMT
FROM:    Genevieve Schroeder at Northwestern University  <genevieveschroeder2023 at u.northwestern.edu>

G. Schroeder, K. D. Alexander, W. Fong, A. Rouco Escorial, (Northwestern),
T. Laskar (U. of Bath), E. Berger (Harvard) report:

"We re-observed the position of short GRB 210726A (Bernardini et al., GCN
30523; Veres et al., GCN 30540; Palmer et al., GCN 30536; Tohuvavohu et
al., GCN 30535) with the Karl G. Jansky Very Large Array (VLA) under
program 20B-057 (PI: Fong) beginning on 2021 August 07.02 UT (11.21 days
post-burst) at a mean frequency of 6 GHz.

In 1.5 hour of observations we detect a radio source with a preliminary
flux density of ~40 uJy. The position of this radio source is fully
consistent with the position of the X-ray afterglow (Osborne et al., GCN
30524; Rouco Escorial et al., GCN 30558) at:

RA(J2000): 12:53:09.8

Dec(J2000): +19:11:25.1

with an uncertainty of 0.6 arcsec in each coordinate.

We obtained further VLA observations at 6 GHz and 10 GHz beginning on 2021
August 14.75 UT (18.94 days post-burst) and detect the source at both
frequencies. We find a significant brightening at 6 GHz, confirming this
source as the radio afterglow of GRB210726A. We note that this radio
afterglow is among the brightest ever detected for a short GRB to date.

Further observations are planned. We thank the VLA staff for quickly
approving and executing these observations."