TITLE:   GCN CIRCULAR
NUMBER:  14302
SUBJECT: GRB130313A: Optical observations from GTC
DATE:    13/03/14 06:55:45 GMT
FROM:    Antonio de Ugarte Postigo at IAA-CSIC  <deugarte@iaa.es>

A. de Ugarte Postigo (IAA-CSIC, DARK/NBI), C.C. Thoene (IAA-CSIC), 
J. Gorosabel (IAA-CSIC), R. Sanchez-Ramirez (IAA-CSIC), J. P. U. Fynbo 
(DARK/NBI) and N. Tanvir (U. Leicester) report:

We have observed the field of the short GRB 130313A (Gompertz et al., 
GCN 14293) using the 10.4m GTC. Observations started at 5:22 UT 
(13.23 hr after the burst) and were performed in the r-band in good conditions 
and a seeing of ~0.8". The combined 8x120s exposure covers the complete 
refined BAT error box (Barthelmy et al., GCN 14296).

We detect a point-like source at the edge of the suggested X-ray afterglow 
(Osborne et al., GCN 14300) for which we estimate a preliminary magnitude 
of r=26.3+/-0.4, as compared with SDSS stars (we note that the photometry is
complicated by a nearby bright star). This object is located at the following 
coordinates (J2000, +/-0.5"):

S1:
R.A.: 15:45:38.45
Dec.: -00:22:03.5

There are two other marginally detected sources consistent with the XRT error 
box, one unresolved at:

S2:
R.A.: 15:45:38.21
Dec.: -00:22:10.3

And one extended:

S3:
R.A.: 15:45:38.64
Dec.: -00:22:04.7

A finding chart with these sources can be found at:
http://www.iaa.es/~deugarte/GRBs/130313A/130313A_GTC.jpg

Further observations in search for variability will be needed to determine the relation 
of any of these sources with GRB 130313A.