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GCN Circular 27276

Subject
GRB 200228B: Mondy, TSHAO, AbAO and CrAO optical observations, afterglow candidate
Date
2020-03-01T15:21:19Z (4 years ago)
From
Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>
A. Pozanenko (IKI), S. Belkin (IKI),  E. Klunko (ISTP), A. Kusakin 
(FAPHI),  I. Reva (FAPHI), V. Rumyantsev (CrAO), R. Ya. Inasaridze 
(AbAO), E. Mazaeva (IKI), A. Volnova (IKI) report on behalf of IKI-GRB-FuN:

We observed the field of GRB 200228B (Laha et al., GCN 27254; Fermi GBM 
Team, GCN 27253) with AZT-33IK 1.5-m telescope of Sayan observatory 
(Mondy) starting on Feb. 28 (UT) 19:24:43. We detected an optical object 
near the enhanced XRT position of the XRT afterglow (Evans et al., GCN 
27256). The object is absent in the Pan-STARRS DR1 catalog. The 
coordinates of the object are (J2000) 16:48:10.88 +16:59:04.5 with 
uncertainty of 0.5 arcsec in both coordinates. Next we observed the 
filed with Zeiss-1000 1-m telescope of Tien Shan Astronomical 
Observatory starting on Feb. 28 (UT) 23:08:56, Abastumani starting on 
Feb. 29 (UT) 01:38:45, Tien Shan Astronomical Observatory starting on 
Feb. 29 (UT) 23:08:56, and CrAO starting on Mar. 01 (UT) 00:58:28.

Preliminary photometry of the object and the field is following.

Date UT start       t-T0  Filter Exp. OT Err UL(3sigma)   telescope
                         (mid, days) (s)
2020-02-28 19:24:43 0.351  R 15*120 21.8  0.3  21.7 AZT-33IK
2020-02-28 23:08:56 0.516  R 3480   n/d   n/d  22.3 Z-1000
2020-02-29 01:38:45 0.616  R 46*60  n/d   n/d  21.8 AS-32
2020-02-29 22:22:37 n/a    R 5040   n/a   n/a  n/a  Z-1000
2020-03-01 00:58:28 1.594  R 31*120 22.05 0.09 23.8 ZTSh


Photometry is based on the USNO-B2.0 nearby stars.
USNO-B1.0    R2
1069-0297786 18.42
1069-0297719 18.25
1069-0297797 14.78

The finding chart is available at 
http://193.232.11.154/GRB200228B/GRB200228B_AZT33IK_Z1000_ZTSh_FC.png 
(or 
http://grb.iki.rssi.ru/GRB200228B/GRB200228B_AZT33IK_Z1000_ZTSh_FC.png ).

We suggest this object is a candidate in the afterglow of GRB 200228B 
after at least two epoch detections (see above), possible variability 
and absence of the bright object (R ~ 22) in the  Pan-STARRS DR1.

We did not detect any object at the position of NIR- candidate (Perley 
and  Cockeram, GCN 27271).
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