[vsnet-grb-info 21142] GRB180914B: Swift UVOT detection of an optical afterglow

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23241
SUBJECT: GRB180914B: Swift UVOT detection of an optical afterglow
DATE:    18/09/16 16:05:06 GMT
FROM:    Paul Kuin at MSSL  <npkuin at gmail.com>

N. Paul M. Kuin reports on behalf of the Swift-UVOT team:

Swift-UVOT has performed follow-up observations of the
Fermi/LAT-detected burst GRB 180914B (Bissaldi et al. GCN Circ. 23232)
in a series of observations tiled on the sky.
Within the error of the location of the XRT source (D'Ai, GCN Circ. 23236)
we detect a source that appears to be fading.
The UVOT source location is RA = 332.2609, Dec = 24.5823 deg which is

RA = 22:09:25.53 (J2000)
Dec = +25:03:43.8 (J2000)

which is consistent with Zheng and Filipenko (GCN Circ. 23237).
The preliminary magnitude using the UVOT photometric calibration
(Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) is

filter Tstart  Tend   exposure magnitude
 u     8.35e4  8.37e4   76.5   18.90 +- 0.23
 u     8.70e4  8.74e4  373.0   18.87 +- 0.11
 u     9.27e4  9.29e4  1.93.8  19.05 +- 0.17A

Times in seconds since Tzero=2018-09-14 18:22:40 UT.

No correction has been made for Galactic interstellar reddening of
E(B-V) = 0.07 (Schlafy&Finkbeiner, 2011 ApJ 737, 103).