TITLE:   GCN CIRCULAR
NUMBER:  37533
SUBJECT: GRB 240821A: radio observation with the VLA
DATE:    24/09/17 15:12:32 GMT
FROM:    Stefano Giarratana at INAF-OAB <s.giarratana@ira.inaf.it>

S. Giarratana (INAF-OAB), M. Giroletti (INAF-IRA),
G. Ghirlanda (INAF-OAB), N. Di Lalla (Stanford Univ.),
N. Omodei (Stanford Univ.), O. S. Salafia (INAF-OAB)

At 04:07:30 UT on 2024 September 6 (T_mid = 15.43 days post-burst)
the Karl G. Jansky VLA observed the field of GRB 240821A
(Fermi GBM team, GCN 37219; SVOM team, GCN 37220, 37226) at a
central frequency of 6, 10 and 15 GHz.

The standard 3C48 was used as bandpass and flux density
calibrator, while J2358-1020 was used as phase calibrator.

From a preliminary analysis, we do not detect the radio counterpart
of GRB 240821A. During the observation, the VLA site was hit by a
thunderstorm, which heavily affected the success of the experiment.
We derive the following upper limits (UL; 3sigma):

==================================================
T_mid   Freq  UL     r.m.s.   Beam        PA
[days]  [GHz] [uJy]  [uJy/b]  [arcsec]    [deg]
==================================================
15.43   6     51     17       1.75x0.93   -38
15.43   10    54     18       0.95x0.62   -29
15.43   15    130    43       0.87x0.38   -44
==================================================

We would like to thank the staff of the VLA for approving, executing,
and processing the observations.

The National Radio Astronomy Observatory is a facility of the National
Science Foundation operated under cooperative agreement by Associated
Universities, Inc.

These observations were carried out as part of project SF171028,
approved in the framework of the Fermi - NRAO joint program agreement.