GCN Circular 22665
Subject
GRB 180418A: Swift/UVOT Detection
Event
Date
2018-04-19T22:05:17Z (8 years ago)
From
Mike Siegel at PSU/Swift MOC <siegel@swift.psu.edu>
M. H. Siegel (PSU) and V. D'Elia (ASDC)
report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 180418A
3086 s after the BAT trigger (D'Elia et al., GCN Circ. 22646).
A fading source consistent with the XRT position
(Goad et al. GCN Circ. 22650)
is detected in the initial UVOT exposures, confirming the previously
reported optical afterglows (Zheng & Filippenko, GCN Circ. 22647; Guidorzi
et al., GCN Circ. 22648; Troja et al., GCN Circ. 22652; Fong et al., GCN
Circ. 22659; Malesani et al., GCN Circ. 22660; Schady et al., GCN Circ. 22662;
Misra et al., GCN Circ. 22663).
The preliminary UVOT position is:
RA (J2000) = 11:20:29.21 = 170.12172 (deg.)
Dec (J2000) = +24:55:59.2 = 24.93311 (deg.)
with an estimated uncertainty of 0.49 arc sec. (radius, 90% confidence).
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) 3087 3236 147 19.19+-0.11
white 3087 4470 344 19.45+-0.09
white 49806 72093 4850 >22.62
v 3243 4835 347 >19.53
b 4064 4264 196 >20.19
b 15510 16114 590 >20.82
u (fc) 3859 4059 196 19.35+-0.24
u 14598 31858 894 >20.73
uvw1 3655 3855 196 19.19+-0.28
uvw1 9720 27635 1206 20.02+-0.21
uvm2 3450 3649 196 18.93+-0.27
uvm2 8814 26975 2165 20.65+-0.26
uvw2 4476 4676 196 >19.69
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).