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).

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