[vsnet-grb-info 11486] GRB 111225A: optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12893
SUBJECT: GRB 111225A: optical observations
DATE:    12/01/21 22:04:47 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen at iki.rssi.ru>

A.Volnova (SAI MSU),  E. Klunko (ISTP),  M. Andreev, A. Sergeev  (Terskol 
Branch of INASAN), A. Pozanenko (IKI) on behalf of  larger GRB follow up 
collaboration report:

We observed the field of GRB 111225A (Siegel et al., GCN 12720) with 
AZT-33IK telescope of Sayan observatory (Mondy) on Dec. 25 between (UT) 
17:37:41 - 18:25:58 in R filter under mean seeing (FWHM) of about 2.0".

We also observed  the field with Zeiss-2000 telescope of Mt. Terskol 
observatory on Dec. 26 between (UT) 17:37:23-18:46:37 in BRI filters under 
poor seeing (FWHM) of about 4.4". On   stacked images of both epochs we did 
not find an optical counterpart (Siegel  et al., GCN 12720; Klotz et al., 
GCN 12722; Adria et al., GCN 12723; Wren et al., GCN 12803).

The photometry is based on the USNO-B1.0 star 1415-0025726 (J2000) 
00:52:35.11 +51:33:58.9, assuming B = 17.56, R =16.50, I = 16.20:

T0+,        Filter,  Exposure,   OT,   UL(3 sigma),    Telescope
(mid, d)             (s)
0.63278     R     24 x 120   n/d   22.5            AZT-33IK
1.58789     B     10 x 90     n/d   22.0            Zeiss-2000
1.60285     R     10 x 90     n/d   21.5            Zeiss-2000
1.61677     I      10 x 90     n/d   20.5            Zeiss-2000

Upper limits above are consistent with upper limits of R~22.5 reported by 
Sonbas et al. (GCN 12740) and observations of the afterglow at R ~ 23.2 on ~ 
1day  after burst trigger (Cenko et al., GCN 12733). Taking into account the 
positive detection of the afterglow on 3.7590 days at R~22.5 (Rumyantsev et 
al., GCN 12793) one can suggest a strong rebrightening of the afterglow 
which is a rare case of  late afterglow (3.7590 days) of an apparently 
nearby burst (cf. UVOT optical detection in uvw2 filter  (Siegel, GCN 
12735).