TITLE:   GCN CIRCULAR
NUMBER:  39760
SUBJECT: GRB 250316A: AbAO AS-32 Optical Upper Limit
DATE:    25/03/17 12:43:30 GMT
FROM:    Nicolai Pankov at HSE, IKI RAS <colinsergesen@gmail.com>

N. Pankov (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI) report on behalf of IKI-GRB-FuN:

We performed optical observations of the field of GRB 250316A (The Fermi GBM team, GCN 39741; Ronchini et. al, GCN 39744; Evans, GCN 39745; Lipunov et. al, GCN 39747; Kennea et. al, GCN 39750; Bala & Meegan, GCN 39751; Beardmore et. al, GCN 39758) in the R filter with the 0.7-meter AS-32 telescope of the Abastumani Astrophysical Observatory (AbAO). The observations started on (UT) 2025-03-17 00:17:41, i.e. about 0.67 days since trigger. We do not find any new optical source within the error circle of the most probable candidate afterglow Swift XRT #1 (Beardmore et. al, GCN 39758). The preliminary upper limit is as follows:

Date       UT start  t-T0         Exp.    Filter OT  UL(3sigma)
                     (mid, days)  (s)
2025-03-17 00:17:41  0.67447      107*60  R      n/d 19.7

The photometry is based on nearby stars from the USNO-B1.0 catalog (R2 magnitudes) and has not been corrected for the Galactic extinction.