TITLE:   GCN CIRCULAR
NUMBER:  35506
SUBJECT: GRB 230818A: further radio observations with the VLA
DATE:    24/01/09 13:30:14 GMT
FROM:    Stefano Giarratana at University of Bologna <s.giarratana@ira.inaf.it>

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


At 22:56:54 UT on 2023 September 18 (T_mid = 31.0 days post-burst)
and at 17:12:33 UT on 2023 November 28 (T_mid = 101.8 days
post-burst) the Karl G. Jansky VLA started observing the field of
GRB 230818A (Fermi GBM team, GCN 34478; Tohuvavohu et al.,
GCN 34479) at a central frequency of 6 and 10 GHz.

The standard J1331+3030 (3C286) was used as bandpass and
flux density calibrator, while J1912+3740 was used as complex
gain calibrator.

From a preliminary analysis, we do not detect the radio counterpart
of GRB 230818A. We derive the following upper limits (UL; 3sigma).

=====================================================
T_mid    Freq     UL     r.m.s.    Beam         PA
[days]   [GHz]   [uJy]   [uJy/b]   [arcsec]     [deg]
=====================================================
31.0     6        24     8         0.34x0.31    -64
31.0     10       24     8         0.22x0.19    -75
101.8    6        30     10        13.2x9.94    -87
101.8    10       24     8         9.05x6.06    -82
=====================================================

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 SF161095,
approved in the framework of the Fermi - NRAO joint program agreement.