TITLE:   GCN CIRCULAR
NUMBER:  30465
SUBJECT: GRB 210704A: Zeiss-1000/SAO-RAS optical observations
DATE:    21/07/17 14:02:10 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

A. Volnova (IKI), A. Moskvitin (SAO RAS),  A. Pozanenko (IKI), N. Pankov 
(IKI, HSE), S. Belkin (IKI, HSE)  report on behalf of GRB IKI FuN:

We observed GRB 210704A  (Ursi et al., GCN 30372; Berretta et al., GCN 
30375; Prasad et al., GCN 30378; D'Ai et al., GCN 30379; Malacaria et 
al., GCN 30380; Ridnaia et al., GCN 30388)  with Zeiss-1000 telescope of 
SAO RAS observatory on 2021-07-11 and  2021-07-13.    We marginally 
detect the optical afterglow (Kim et al., GCN 30384; D'Avanzo et al., 
GCN 30385; Troja et al., GCN 30390; Kann et al., GCN 30391, 30401; Sun 
et al., GCN 30411; D'Avanzo et al., GCN 30432; Rastinejad  et al., GCN 
30433;  Watson et al., GCN 30436; Pankov et al., GCN 30440; Troja et 
al., GCN 30442; Kann et al., GCN 30443; Fong et al., GCN 30445; O'Connor 
et al., GCN  30451).

Preliminary photometry of the afterglow is following

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

2021-07-11 18:38:22   6.98262 R      12*300  23.1    0.3   23.2
2021-07-13 18:16:08   8.94635 R      24*300  23.8   S/N=2  23.5

The photometry is based on nearby USNO_B-1.0 stars
USNO_B-1.0_id R2
1471-0248922 16.31
1471-0248878 17.04