[vsnet-grb-info 19352] GRB 170428A: Swift/UVOT Upper Limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21049
SUBJECT: GRB 170428A: Swift/UVOT Upper Limits
DATE:    17/04/29 00:40:35 GMT
FROM:    Paul Kuin at MSSL  <npkuin at gmail.com>

N. P. M. Kuin (UCL-MSSL) and A. P. Beardmore (U. Leicester) report
on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 170428A
740 s after the BAT trigger (Beardmore et al., GCN Circ. 21042).
No optical afterglow consistent with the XRT position (Beardmore
et al., GCN Circ. 21047) is detected in the initial UVOT exposures.
Preliminary 3-sigma upper limits using the UVOT photometric system
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures
are:

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

v                  740        16576         1101         >20.0
b                  838        10823         1101         >21.0
u                  813         5412          299         >19.5
w1                 789         5207          216         >19.5
m2                 764        17481         1102         >20.1
w2                4392        11731         1082         >20.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.06 in the direction of the burst
(Schlegel et al. 1998).