TITLE:   GCN CIRCULAR
NUMBER:  33595
SUBJECT: GRB 230409B: Swift/UVOT Detection
DATE:    23/04/09 14:26:27 GMT
FROM:    Paul Kuin at MSSL  <npkuin@gmail.com>

GRB 230409B: Swift/UVOT Detection

N. Paul Kuin (UCL/MSSL) and A. P. Beardmore (U. Leicester) report
on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of
GRB 230409B  386 s after the BAT trigger (Beardmore et al.,
GCN Circ. 33592).  A weak fading source consistent with the
XRT position (Beardmore et al. GCN Circ. 33592) is detected
in the initial UVOT exposures at position RA=329.5158,
Dec=52.8321 deg.

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              386          536          147         19.35 +/- 0.20
v                  542         1931          156        >18.1
b                  642         2029          156        >19.4
u                  616         2004          156        >19.0
w1                 592         1980          156        >18.8
m2                 567         1955          156        >19.2
w2                 692         1906          136        >20.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 1.226 in the direction of the burst
(Schlegel et al. 1998).