[vsnet-grb-info 28415] GRB 210724A: Zeiss-1000 of Koshka observatory, optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30518
SUBJECT: GRB 210724A: Zeiss-1000 of Koshka observatory, optical upper limit
DATE:    21/07/26 12:14:12 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

S. Belkin (IKI),  A. Novichonok (Petrozavodsk State University, KIAM), 
  A. Pozanenko (IKI), A. Zhornichenko (KIAM),  N. Pankov (HSE)  report 
on behalf of IKI GRB FuN:

We observed the field of  GRB 210724A (D'Avanzo et al. GCN 30497) with 
Zeiss-1000 telescope of Koshka observatory starting on July 24 (UT) 
20:39:32. We do not detect any object XRT error circle (D'Avanzo et al. 
GCN 30497). We also not detect the object at the position of the 
afterglow candidate (Ugarte Postigo et al., GCN 30511).

Preliminary photometry of the field is following

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

2021-07-24 20:39:32   0.024919    R     21*60   n/d  n/d   18.6

The photometry is based on the nearby USNO-B1.0 stars
USNO-B1.0_id R2
USNO-B1.0_id R2
0837-0267865 15.24
0836-0268753 16.95
0837-0267827 15.54