[vsnet-grb-info 28281] GRB 210704A: Assy optical afterglow candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30384
SUBJECT: GRB 210704A: Assy optical afterglow candidate
DATE:    21/07/05 20:32:34 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

V. Kim (FAI, Pulkovo Observatory), A. Pozanenko (IKI), M. Krugov (FAI), 
   S. Belkin (IKI), N. Pankov (HSE, IKI) report on behalf of GRB IKI FuN:

We observed the field of  GRB 210704A Fermi-LAT (Berretta et al. 2021, 
GCN 30375), AGILE/MCAL (Ursi et al. 2021, GCN 30372), AstroSat/CZTI 
(Prasad et al. 2021, GCN 30378), Swift/XRT (D'Ai et al. GCN 30379), and 
Fermi-GBM (Malacaria et al. GCN 30380) with AZT-20 telescope of 
Assy-Turgen observatory starting on 2021-07-05 (UT) 17:42:41.27.

In a stacked image we detect only one object  near enhanced XRT position 
(D'Ai et al. GCN 30379). Coordinates of the object are (J2000) 
10:36:04.88 +57:12:58.5 with uncertainty of 0.5 arcsec in both coordinates.

Preliminary photometry of the object is following

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

2021-07-05 17:42:41.27  0.94407  66*60  r'      22.25  0.13  23.0

The photometry is based on the nearby SDSS-DR12 stars.
The object is not presented in the SDSS DR12, nor in PS1 catalogue. We 
suggest the object is the afterglow of GRB 210704A.