TITLE:   GCN CIRCULAR
NUMBER:  31876
SUBJECT: GRB 220403B: Swift/UVOT Detection
DATE:    22/04/11 17:51:22 GMT
FROM:    Noel Klingler at NASA-GSFC / UMBC  <njk5441@psu.edu>

N. J. Klingler (NASA-GSFC/UMBC/CRESST II) reports on behalf of the
Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 220403B
105 s after the BAT trigger (Klingler et al., GCN Circ. 31820).
A source consistent with the XRT position
is detected in the initial UVOT exposures.

The UVOT position is:
    RA  (J2000) =  12:45:53.46 = 191.47274 (deg.)
    Dec (J2000) = +89:11:06.5  =  89.18515 (deg.)
with an estimated uncertainty of 0.52 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              105          255          147         19.86 +/- 0.12
v                  647         1074           58        >18.6
b                  573          766           39        >19.3
u                  318          741          265         19.93 +/- 0.22
w1                 697          716           19        >18.9
w2                 797         1049           39        >19.9

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.208 in the direction of the burst
(Schlegel et al. 1998).