TITLE:   GCN CIRCULAR
NUMBER:  27182
SUBJECT: GRB 200224A: Swift/UVOT Detection
DATE:    20/02/24 21:40:15 GMT
FROM:    Frank Marshall at Swift/UVOT  <marshall@milkyway.gsfc.nasa.gov>

F. E. Marshall (NASA/GSFC) and T. N. Ukwatta (LANL)
report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 200224A
101 s after the BAT trigger (Ukwatta et al., GCN Circ. 27173).
A source consistent with the enhanced XRT position
(Gropp et al., GCNC 27179) and the optical positions reported
by Sota et al. (GCNC 27176) and Stecklum et al. (GCNC 27177)
is detected in the initial UVOT exposures.
The source is very close to the edge of the image in the
first exposure at 101 s after the BAT trigger, and further
analysis is required to determine an accurate intensity
for that exposure.

The preliminary UVOT position is:
    RA  (J2000) =  16:35:04.14 = 248.76727 (deg.)
    Dec (J2000) = +41:36:42.3  =  41.61174 (deg.)
with an estimated uncertainty of 0.43 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

u                  259          509          246         18.75 +/- 0.10
white              861         1011          147         20.57 +/- 0.20
w1                5978        19265         1098        >20.7
m2                5772        18542         1279        >21.4
w2                5363        30092         1953        >21.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.005 in the direction of the burst
(Schlegel et al. 1998).