TITLE:   GCN CIRCULAR
NUMBER:  14472
SUBJECT: GRB130427A: Swift/UVOT followup observations of an Optical Afterglow
DATE:    13/04/27 20:22:45 GMT
FROM:    Tyler Pritchard at PSU  <tapritchard@astro.psu.edu>

T. Pritchard (PSU), A. Maselli (INAF-IASFPA), N. P. M. Kuin (MSSL),
S. R. Oates (MSSL-UCL), M. De Pasquale (MSSL-UCL),
and M. H. Siegel (PSU), report on behalf of the Swift/UVOT team:

Further to Maselli et al., GCN Circ. 14448 we have performed manual
stacking and aspect corrections on the initial UVOT image.  These
resulting images still retain some instrumental effects due to the
brightness of the object and loss of star tracking lock.

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

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag
wh          1522         1542           19.5         13.8±1.1
v         382          401           19.5        12.1±0.04
b            480          500           19.5        12.6±1.09
u            456          475           19.5        11.8±1.09
w1           430          450           19.5        11.2±0.04
m2           406          426           19.5        11.2±0.04
w2           358          377           19.5        11.2±0.04

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.24 in the direction of the burst
(Schlegel et al. 1998).