[vsnet-grb-info 27589] GRB 210321A: CrAO optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29692
SUBJECT: GRB 210321A: CrAO optical upper limit
DATE:    21/03/22 19:02:33 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

N. Pankov (HSE), S. Nazarov (CrAO), A. Pozanenko (IKI),  S. Belkin (IKI) 
report  on behalf of GRB IKI FuN:

We observed the field of GRB 210321A (Dichiara  et al., GCN 29677)  with 
AZT-8 telescope of CrAO observatory starting on 2021-03-21 (UT) 
19:04:11. The optical afterglow (Siegel  et al., GCN 29679; Butler et 
al., GCN 29680;   Lipunov et al., GCN 29683; Heintz et al., GCN 29684; 
de Ugarte Postigo et al., GCN 29685; Xin et al. GCN 29687; Pankov et 
al., GCN  29689) is not detected in a combined image. Preliminary 
photometry of the field  is following

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

2021-03-21 19:04:11   0.51238    R      55*60  n/d  n/d   20.8

The photometry is based on the nearby USNO-B1.0 stars
USNO-B1.0_id R2
1601-0068003 15.84
1600-0068970 16.18
1601-0068018 16.54
1601-0067995 16.23