GCN Circular 18131
Subject
GRB 150811A: Swift/UVOT further observations
Date
2015-08-12T12:14:43Z (9 years ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
N. P. M. Kuin (UCL-MSSL) and P. A. Evans (U Leicester)
report on behalf of the Swift/UVOT team:
We report further on the Swift/UVOT observations of GRB 150811A which
began 148 s after the BAT trigger (Evans et al., GCN Circ. 18119).
A source consistent with the XRT position (Goad et al. GCN Circ. 18124)
was reported earlier in the optical/ir by Butler et al.(GCN Circ. 18120)
Zheng et al. (GCN Circ. 18121), Kuin et al.(GCN Circ. 12122), Japelj et
al., (GCN Circ. 12123), Perley and Cenko (GCN. Circ. 12125), Moskivitin
(GCN Circ. 12128). Our initial observations in the white filter show a
rise from the start at 147s around magnitude (white) 21 which continues
in the u band event data and starts leveling off around magnitude 17.8
550s after the trigger, consistent with the report by Perley and Cenko.
The data taken during the next orbit show that the decay had already
set in. The uv bands showed marginal count rates in all three bands
initially below the 3-sigma level, suggesting the burst is at low redshift.
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_FC 148 297 147 20.39 +/- 0.23
u_FC 306 549 239 18.19 +/- 0.11
white 4424 4624 197 19.16 +/- 0.07
u 5449 5854 197 18.83 +/- 0.16
v 4835 5034 197 18.89 +/- 0.17
b 4219 4419 197 19.31 +/- 0.14
w1 5244 11888 1082 >20.6
m2 5039 10981 1082 >21.1
w2 4630 6265 393 >20.5
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.17 in the direction of the burst
(Schlegel et al. 1998).