TITLE:   GCN CIRCULAR
NUMBER:  20484
SUBJECT: GRB 170117A: Swift/UVOT Upper Limits
DATE:    17/01/19 12:38:02 GMT
FROM:    Alice Breeveld at MSSL-UCL  <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and A. Melandri (INAF-OAB)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170117A
86251 s after the BAT trigger (Palmer, GCN Circ. 20480).
No optical afterglow consistent with the BAT position given in that 
circular is detected in the initial UVOT exposures.
The preliminary 3-sigma upper limit using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial summed 
exposures is:

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

white            86251       116034         2654         >22.0

The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.35 in the direction of the 
burst (Schlegel et al. 1998).