TITLE:   GCN CIRCULAR
NUMBER:  33711
SUBJECT: GRB 230427A: TSHAO, SAO RAS, AbAO optical upper limit
DATE:    23/04/28 21:28:46 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>

I. Reva (FAP), A. S. Moskvitin (SAO RAS), O. A. Maslennikova (SAO RAS), R. Ya. Inasaridze (AbAO), A. Volnova (IKI), A. Pozanenko (IKI), N. Pankov (HSE), S. Belkin (IKI) report on behalf of GRB IKI FuN:

We observed the field of Swift GRB 230427A (Troja et al., GCN 33687) in R-filter on 2023-04-27 starting (UT) 15:09:59 with with Zeiss-1000 telescope of TSHAO observatory, (UT) 17:21:56 with Zeiss-1000 telescope of SAO RAS, (UT) 21:56:16 with AS-32 telescope  of Abastumani observatory. We do not detect the optical counterpart of GRB 230427A (Troja et al., GCN 33687; Hu et al., GCN 33695; Agui Fernandez et al., GCN 33704; Klingler et al., GCN 33710). Preliminary photometry of stacked images is following

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

2023-04-27 15:09:59 0.22388  37*120 R      n/d  n/d   21.8     TSAHO
2023-04-27 17:21:56 0.30117   4*300 R      n/d  n/d   21.4     SAO RAS
2023-04-27 21:56:16 0.51140 104*60  R      n/d  n/d   21.0     AbAO

The photometry is based on nearby USNO-B1.0 stars.
USNO-B1.0    R2
1381-0248742 15.71
1381-0240666 16.93
1381-0240629 16.83