GCN Circular 26574
Subject
GRB 191221B: Swift/UVOT Detection
Event
Date
2019-12-24T12:08:39Z (6 years ago)
From
Paul Kuin at MSSL <npkuin@gmail.com>
N. P. M. Kuin (UCL-MSSL) and S. L. Laha (GSFC/UMBC/CRESST)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 191221B
92 s after the BAT trigger (Laha et al., GCN Circ. 26534).
A source consistent with the XRT position (Beardmore et al. GCN Circ. 26540)
and ALMA position (Laskar et al., GCN Circ. 26564) was detected in the
initial UVOT exposures.
The preliminary UVOT position is:
RA (J2000) = 10:19:19.24 = 154.83017 (deg.)
Dec (J2000) = -38:09:27.64 = -38.15768 (deg.)
with an estimated uncertainty of 0.42 arc sec. (radius, 90% confidence).
Preliminary detections 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 92 241 147 see below
u 304 554 246 12.30 +/- 0.02
b 560 579 20 13.54 +/- 0.04
uvw2 610 630 20 13.20 +/- 0.06
v 635 655 20 13.42 +/- 0.05
uvm2 659 679 20 12.79 +/- 0.06
uvw1 684 704 20 12.82 +/- 0.05
Aperture photometry shows initially a completely saturated detector,
leading
to wh < 13.8 mag. The first exposure in the white filter (tstart=T0+92s)
shows a readout streak but the readout streak traverses also another
relatively bright star which leads to a saturated readout streak
and precludes using that method of determining the magnitude (Page
et al, 2013 MNRAS 436, 1684). Analysis continues.
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.08 in the direction of the burst
(Schlegel et al. 1998).