TITLE:   GCN CIRCULAR
NUMBER:  36179
SUBJECT: GRB 240411B: Swift/UVOT Detection
DATE:    24/04/19 12:32:47 GMT
FROM:    Sam LaPorte at PSU <sjl5346@psu.edu>

S. J. LaPorte (PSU) and T. M. Parsotan (GSFC)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 240411B
190 s after the BAT trigger (Parsotan et al., GCN Circ. 36063). A source
consistent
with the XRT position (Goad et al., GCN Circ. 36065) and the reported
optical transient (Izzo et al. GCN 36064; Schneider et
al. GCN 36067; Ror et al. GCN 36069; Ugarte Postigo et al. GCN 36074; Aryan
et al. GCN 36077; Pankov et al. GCN 36078) is detected in the initial UVOT
exposures.

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                      6480          6680           196        >19.84
v                      7096          7295           196        >18.58
uvw2                6891          7091           196        >19.45
white                6685          6885           196        >20.54
white                 198            348           147           20.08+-0.27


The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.022 in the direction of the burst
(Schlegel et al. 1998).