[vsnet-grb-info 16911] GRB 150821A: Swift/UVOT Detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18192
SUBJECT: GRB 150821A: Swift/UVOT Detection
DATE:    15/08/21 19:28:53 GMT
FROM:    Paul Kuin at MSSL  <npkuin at gmail.com>

N. P. M. Kuin (UCL-MSSL) and E. Troja (NASA/GSFC/UMCP) report on behalf
of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 150821A
251 s after the BAT trigger (Troja et al., GCN Circ. 18186).  We use the
UVOT position as reported there which is consistent with the enhanced
XRT position  (Goad et al. GCN Circ. 18191).

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

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

white              251          401          147         16.59 +/- 0.03
v                  560          580           20         17.21 +/- 0.18
b                  484          504           19         17.48 +/- 0.12
u                  460          479           19         16.70 +/- 0.11
w1                 435          629           39         17.62 +/- 0.18
m2                 410         7287          372        >19.8
w2                 535         1904          156         19.85 +/- 0.28

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.02 in the direction of the burst
(Schlegel et al. 1998).