TITLE:   GCN CIRCULAR
NUMBER:  22004
SUBJECT: GRB 171010A: Swift/UVOT Detection
DATE:    17/10/12 13:22:35 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and M. H. Siegel (PSU)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 171010A
69338 s after the LAT trigger (Omodei et al., GCN Circ. 21985).
A afterglow (Thorstensen and Halpern, GCN Circ. 21987, Izzo and 
Malesani, GCN Circ. 21988, Guidorzi et al., GCN Circ. 21991, Malesani et 
al., GCN Circ. 22000, Harita et al., GCN Circ. 22001) is detected in the 
initial UVOT exposures. However it is not possible to distinguish this 
source from the position of the Pan-STARRS source given in Izzo and 
Malesani (GCN Circ. 21988). The source magnitude is not changing 
significantly within this observation.

Preliminary detections using the UVOT photometric system (Breeveld et 
al. 2011, AIP Conf. Proc. 1358, 373) for the summed exposures are:

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

white            69338        80991         4818         18.84 ± 0.02

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.15 in the direction of the 
burst (Schlegel et al. 1998).