TITLE:   GCN CIRCULAR
NUMBER:  15744
SUBJECT: GRB 140108A: Mondy optical observations, refined analysis
DATE:    14/01/15 17:37:02 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

A.Volnova (IKI), E. Klunko (ISTP), M. Eselevich(ISTP), A. Pozanenko(IKI) 
report on behalf of larger GRB follow-up collaboration:

We analyzed observations of AZT-33IK telescope of Sayan observatory, 
Mondy (Klunko et al., GCN 15704; Volnova et al., GCN 15713) of the 
Swift GRB 140108A (Racusin et al., GCN 15699).  Using bright time 
interval of the afterglow we calculated coordinates of the OT:

RA(J2000)=   21:40:26.75
RA(J2000)=  +58:44:41.3
with uncertainty of 0.4 arcsec of each coordinate.

The OT coordinates are within the enhanced XRT position (Osborne et al., 
GCN 15705) and compatible with positions reported early (Gorbovskoy et 
al., GCN 15701; Strobl et al., 15703).

The light curve of the afterglow can be found in 
http://grb.rssi.ru/GRB140108A/GRB140108A_lc_preliminary.png.

The photometry is based on USNO-B1.0 stars:
s1	1487-0322168	21:40:30.85	+58:43:53.1	18.18
s2	1487-0322049	21:40:20.16	+58:43:58.3	17.96
s3	1487-0322069	21:40:21.62	+58:45:00.6	17.29
s4	1487-0322305	21:40:41.61	+58:45:28.0	15.73

Maximum of afterglow brightness of R=18.50 +/- 0.08 was detected at 
0.00468 days after GRB trigger. It is also interesting a sharp drop at 
~0.85 days (confirmed by observations reported by Kelemen (GCN 15727)) 
which could be related to a jet break observed in XRT light curve (see 
http://www.swift.ac.uk/xrt_live_cat/00583338/).