[vsnet-grb-info 20711] GRB 180618A: TSHAO optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22809
SUBJECT: GRB 180618A: TSHAO optical upper limit
DATE:    18/06/20 17:57:39 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

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

We observed the field of GRB GRB 180618A (LaPorte et al., GCN 22790) 
with Zeiss-1000 1-m telescope of Tien Shan Astronomical Observatory 
starting on June 18 (UT) 15:39:19. We obtained several images in 
R-filter.  The optical afterglow (LaPorte et al., GCN 22790; Guidorzi et 
al., GCN 22792; Tyurina et al., GCN 22797)  is not detected in a stacked 
image. Preliminary photometry of the field is following.

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

2018-06-18  15:39:19 0.65209  R      36*120  n/d  n/d    22.2

The photometry is based on several nearby SDSS-DR10 stars.

Ref.stars
SDSS_id             R(Lupton)
J112037.79+735136.8 17.37
J111905.28+734733.2 17.54
J111907.19+734657.8 17.04