TITLE:   GCN CIRCULAR
NUMBER:  3817
SUBJECT: GRB050815: Optical afterglow detection by Swift UVOT
DATE:    05/08/16 03:21:26 GMT
FROM:    Patricia Schady at MSSL/Swift  <ps@mssl.ucl.ac.uk>

P. Schady (MSSL/PSU), D. Fox (PSU), P. Roming (PSU), A. Cucchiara (PSU), 
M. Still (GSFC), S.T. Holland (GSFC/USRA) K. Mason (MSSL), A. Blustin 
(MSSL), N. Gehrels (GSFC), on behalf of the Swift UVOT team

The Swift Ultra-Violet Telescope (UVOT) began observations of GRB050815 on 
August 15th, 2005 at 17:26:25.6 UT, 67s after the BAT trigger. The UVOT 
took a 100s exposure in the V band and two 10s exposures in the M1 and W2 
UV filters before the source was occulted by the Earth. The next set of 
observations were made ~1hr after the BAT trigger.

Anylsis of the early time data reveals an uncatalogued source in the V 
band at position

Ra, Dec = 19:34:23.147, +09:08:47.47

with an estimated uncertainty of 0.5". Astrometry was performed using 
stars from the USNO-catalogue. The source is no longer detected in the 
second epoch of V band images, confirming it's fading nature, and leading 
us to conclude this to be the afterglow. No detections are made in any 
other of the UVOT filters at the 3-sigma significance level. 

Photometry carried out on this source requires additional care due to the 
proximity ofvarious bright stars (~16-18mag). We estimate the afterglow to 
have decayed by about 1 magnitude in 1 hour. Further analysis is still
undergoing.