GCN Circular 23360
Subject
GRB 181020A: Swift/UVOT Detection
Event
Date
2018-10-21T18:39:11Z (8 years ago)
From
Jeffrey Gropp at PSU <jdg44@psu.edu>
J. D. Gropp (PSU), M. De Pasquale
(U. Instanbul) and Moss (George Washington University)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 181020A
122 s after the BAT trigger (Moss et al., GCN Circ. 23349).
A fading source consistent with the XRT enhanced position
(Goad et al. GCN Circ. 23351)
is detected in the initial UVOT exposures.
The preliminary UVOT position is:
RA (J2000) = 00:55:55.77 = 13.98239 (deg.)
Dec (J2000) = -47:22:51.9 = -47.38108 (deg.)
with an estimated uncertainty of 0.45 arc sec. (radius, 90% confidence).
This optical afterglow is also reported by VLT/X-shooter, Fynbo et al., GCN
Circ. 23356;
LCO Cerro Tololo, Cucchiara et al., GCN Circ. 23358; and its position is
consistent
with the Fermi LAT Measurement reported in, Axelsson et al., GCN Circ.
23350;
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
b 352 1027 97
17.18+-0.07
m2 427 745 58 >18.06
u_fc 96 6797 768
18.52+-0.09
u 96 346 245
17.60+-0.08
v 21 720 67
14.89+-0.04
w1 452 769 58 >18.20
w2 379 1053 97 >18.56
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.01 in the direction of the burst
(Schlegel et al. 1998).
We note that the non-detection in the UV filters is expected for a source
at the reported
redshift z=2.94 (VLT/X-shooter, Fynbo et al., GCN Circ. 23356;), given
the Lyman forest absorption by intergalactic hydrogen.