TITLE:   GCN CIRCULAR
NUMBER:  23177
SUBJECT: GRB 180818B: TSHAO optical upper limit
DATE:    18/08/26 16:17:39 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

E. Mazaeva (IKI), A. Pozanenko (IKI),  A. Kusakin (FAPHI), I. Reva 
(FAPHI),  A. Volnova (IKI), M. Krugov (FAPHI) report on behalf of larger 
GRB follow-up collaboration:

We observed the field of GRB 180818B  (Marshall et al., GCN 23149; Veres 
et al., GCN 23153) with Zeiss-1000 1-m telescope of Tien Shan 
Astronomical Observatory starting on August 08 (UT) 22:20:38. We 
obtained several images in R-filter.  Within enhanced XRT Swift-XRT 
position (Beardmore et al., GCN 23151)  we do not detect any object.  In 
  particular we do not detect the afterglow candidate reported in  GCN 
23161 (Hu et al.) Preliminary photometry of the field is following.

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

2018-08-18  22:20:38 0.42710  R      36*60  n/d  n/d    20.4

The photometry is based on several nearby USNO-B1.0 stars.