TITLE:   GCN CIRCULAR
NUMBER:  33114
SUBJECT: GRB 221226B: Swift-UVOT Detection
DATE:    22/12/27 17:23:08 GMT
FROM:    Noel Klingler at NASA-GSFC / UMBC  <njk5441@psu.edu>

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

The Swift-UVOT began settled observations of the field of GRB 221226B
76 s after the BAT trigger (Cenko et al., GCN Circ. 33108).  A source
consistent with the XRT position (Goad et al., GCN Circ. 33109) and consistent
with the  optical  counterpart reported by VLT/X-shooter
(Xu et al., GCN Circ. 33110) 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

white               76          226          147         20.54 +/- 0.22
v                 4408         4608          197        >19.3
b                 3793         3993          197        >20.0
u                  288         5132          278        >20.1
w1                4818         5018          197        >20.0
m2                4613         4813          197        >19.5
w2                4204         4404          197        >20.0

The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.017 in the direction of the burst
(Schlegel et al. 1998).