TITLE:   GCN CIRCULAR
NUMBER:  42299
SUBJECT: GRB 251013D: Swift/UVOT Observations
DATE:    25/10/15 20:20:03 GMT
FROM:    Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>

M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 251013D 71 ks after the Fermi/GBM trigger (GCN Circ. 42224; DeLaunay et al., GCN Circ. 42244). We detect an uncatalogued optical source near the position of XRT source #2 (Burrows et al., GCN Circ. 42291). There is no evidence of fading in the UVOT data thus far.

The preliminary UVOT position is:
    RA  (J2000) =  03:07:52.73 =  46.96971 (deg.)
    Dec (J2000) = +08:48:57.4  =   8.81595 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).

Preliminary detections and 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: 

Filter         T_start(s)   T_stop(s)      Exp(s)           Mag

white            71081        72734         1622      20.98+/-0.16
white            76655        78444         1758      20.78+/-0.13
white            82245        83695         1423      20.68+/-0.13

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.312 in the direction of the burst
(Schlegel et al. 1998).