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GCN Circular 30972

Subject
GRB 211023B: TSHAO optical observation
Date
2021-10-24T13:54:08Z (2 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
A. Pozanenko (IKI), I. Reva (FAP), M.Krugov (FAP), S. Belkin (IKI), V. 
Kim (FAP),  N. Pankov (HSE) report on behalf of GRB-IKI-FuN:

We observed the field of possible short GRB 211023B detected by Swift 
(Dichiara  et al., GCN  30960)  with Zeiss-1000 telescope of Tien Shan 
Astronomical Observatory stating on Oct. 23 (UT) 21:17:06. We obtained 
series with 120 sec expositions in R-filter.

Within enhanced Swift-XRT position  (Beardmore et al., GCN  30966) we do 
not detected any source (see upper limits below). In particular we do 
not detect possible optical afterglow (Dichiara  et al., GCN  30960). 
  Preliminary photometry of   stacked images   is following

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

2021-10-23 21:17:06 0.01127  R      5*120 n/d n/d     18.9
2021-10-23 21:17:06 0.02238  R     21*120 n/d n/d     19.5

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

In addition we found a source in Legacy Survey 
(https://www.legacysurvey.org) which is coincident with UVOT detection 
(Dichiara  et al., GCN  30960).
This is a point-like object at ~0.67 arces distance from UVOT position 
and has a LS DR9 photometry
g=24.32, r=24.36, z=23.31
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