[vsnet-grb-info 15491] GRB 140818B: TShAO optical upper limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16780
SUBJECT: GRB 140818B: TShAO optical upper limit
DATE:    14/09/05 06:16:20 GMT
FROM:    Alexei Pozanenko at IKI  <alex at grb.rssi.ru>

A. Pozanenko (IKI), I. Rewa, W. Mundrzyjewski, A. Kusakin (Fesenkov Astrophysical Institute), A. Volnova (IKI),  report on behalf of larger GRB follow-up collaboration:

We observed the field of the Swift GRB 140818B  (Vargas et al., GCN 16709)with Zeiss-1000 (East) telescope of Tien Shan Astronomical Observatory starting on Aug. 19, (UT) 17:05. We took several images in R-filter.  Within enhanced XRT error circle  (Beardmore et al., GCN 16712) we do not detect the afterlow (Aceituno et al., GCN 16711; Knust et al., GCN 16713). The source mentioned by Knust et al. (GCN 16713) is clearly visible in a stacked image in coordinates (J2000) 18:04:32.76 -01:23:08.9 (uncertainty  is 0.2 arcsec in both coordinates)  and has brightness of R=22.1+/-0.1.

Details of a photometry of the stacked image are following

Date       UT start  t-T0,d  Exp,s   Filter Up_Lim (3 sigma)
                     (mid)

2014-08-19 16:11:12  0.9317  20*600  R      22.9


The photometry is based on nearby USNO-B1.0 stars, R2 magnitudes.