[vsnet-grb-info 28427] GRB 210725A: AbAO optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30530
SUBJECT: GRB 210725A: AbAO optical upper limit
DATE:    21/07/27 06:54:14 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

N. Pankov (HSE, IKI),  R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI), 
S. Belkin (IKI), V. R. Ayvazian (AbAO),  G. V. Kapanadze (AbAO), report 
on behalf of GRB IKI FuN:

We observed  the field of GRB 210725A (Bernardini et al. GCN 30501; 
Torii  et al. GCN 30507; Poolakkil et al. GCN 30519)  with AS-32 
telescope of Abastumani observatory (AbAO) in R-filter starting on July, 
25 (UT) 19:11:58. We do not detect any object in the enhanced XRT 
position (Perri et al. GCN 30517). The non detection is consistent with 
optical observations (Zheng  et al. GCN 30503; Niwano et al., GCN 30509; 
Siegel  et al. GCN 30527).

Preliminary photometry of the field  is following

Date       UT start   t-T0    Filter Exp.    OT   Err.  UL(3sigma)
                        (mid, days)    (s)

2021-07-25 19:11:58   0.65481  R     36*60   n/d  n/d   20.8

The photometry is based on the nearby stars:
USNO-B1.0 R2
USNO_B10_id R2
0888-00234198 14.31
0888-00234167 15.25