TITLE:   GCN CIRCULAR
NUMBER:  43963
SUBJECT: GRB 260131A/B: radio detection with the VLA
DATE:    26/03/11 16:32:24 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),
L. Nava (INAF-OAB)

At 00:39:44 UT on 2026 February 5 (T_mid = 4.78 days
post-burst) the Karl G. Jansky VLA observed the field of
GRB 260131A/B (Fermi GBM team, GCN 43579, 43585; Sugai et
al., GCN 43580; Konus-Wind team, GCN 43590; Insight-HXMT
team, GCN 43591; GRID Collaboration, GCN 43605) in three
bands, with central frequencies of 6, 10 and 15 GHz.

The standard 3C48 was used as bandpass, flux density
and phase calibrator.

From a preliminary analysis, an unresolved radio source
is detected at a position (J2000):

RA: 01:38:51.308 +- 0.001
Dec: +34:19:40.84 +- 0.01

consistent with the X-ray (Sugai et al., GCN 43580;
Jiang et al., GCN 43600;), optical (GOTO collaboration,
GCN 43586; Lee et al., GCN 43587; García García, GCN 43599;
Jayaraman et al., GCN 43606; Zhu et al., GCN 43607; KAIT
GRB team, GCN 43609; MISTRAL GRB collaboration, GCN 43610;
Volnova et al., GCN 43632, 43670; Gupta et al., GCN 43708)
and infrared (Shi et al., GCN 43601) position of the
transient.

The preliminary analysis yields the following results:

================================================================
T_mid	Freq	Peak	r.m.s.	Beam		PA
[days]	[GHz]	[uJy/b]	[uJy/b]	[arcsec^2]	[deg]
================================================================
4.78	6	669	6	0.94x0.34	74
4.78	10	1018	6	0.60x0.21	70
4.78	15	1671	9	0.49x0.15	68
================================================================

No source is detected with a >3sigma confidence level at the
aforementioned position in the VLASS.

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 SF181027,
approved in the framework of the Fermi - NRAO joint program agreement.