[vsnet-grb-info 16286] GRB 150222A: CrAO optical observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17567
SUBJECT: GRB 150222A: CrAO optical observation
DATE:    15/03/11 21:13:05 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

V. Rumyantsev (CrAO), E. Mazaeva (IKI),  A. Volnova (IKI), A. Pozanenko 
(IKI) report on  behalf of larger GRB follow-up collaboration:

We observed the field of the Swift GRB GRB 150222A (Bernardini et al., 
GCN 17486) with ZTSh telescope of CrAO observatory starting on
Feb. 22 (UT) 23:19:54. We took several images in R-filter of 120 s 
exposure under non-optimal weather conditions and mean seeing of 4". 
Within enhanced  XRT position (Beardmore et al., GCN 17494) we detect a 
source in coordinates (J2000) 13 15 08.74 -12 09 07.2 with uncertainty 
of 0.4 arcsec in both coordinates. The source position is coincident 
with the optical afterglow candidate (Nicuesa Guelbenzu et al., GCNs 
17495, GCN 17506).  Photometry of the source in a combined image is 
following

Date       UT start,  t-t0     Filter   Exp.    OT   OT_err UL(3sigma)
                       (mid, days)        (s)

2015-02-22 23:19:54   0.2913   R        34*120  23.0 0.3    23.3

The photometry is based on USNO-B1.0  star 0778-0337957 (J2000) 13 15 
05.41 -12 08 17.5 assuming R2=15.31

Taking into account photometry of the source r' = 24.6+/-0.3 at ~0.42 
days reported by Nicuesa Guelbenzu et al. (GCN 17495) one could suggest 
the source is the optical afterglow of GRB 150222A.

The source reported in GCN 17489 (Mazaeva et al) is clearly visible in 
coordinates (J2000) 13 15 08.30 -12 08 57.5 with uncertainty of 0.4 
arcsec in both coordinates. A photometry of the source is R=22.12+/-0.12.