TITLE:   GCN CIRCULAR
NUMBER:  38008
SUBJECT: GRB 241030B: Swift/UVOT Detection
DATE:    24/10/31 12:56:29 GMT
FROM:    Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>

A. A. Breeveld (UCL-MSSL) and N. J. Klingler (GSFC/UMBC/CRESSTII) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 241030B 162 s after the BAT trigger (Klingler et al., GCN Circ. 37981).
The optical counterpart (Fu et al., GCN Circ. 37985; Odeh et al., GCN Circ. 37986; Moskvitin et al., GCN Circ. 37987; Brivio et al., GCN Circ. 37991;  Moskvitin et.al GCN Circ. 37995 and Qui et al. GCN Circ. 37999) is detected in the initial UVOT exposure in the white filter only.

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              162          538          167         21.00 ± 0.30
v                  395         4817          255        >19.4
b                  494          857           58        >19.3
u                  469         5380          203        >20.2
w1                 444         5228          255        >21.1
m2                4822         5021          197        >19.7
w2                 371         4612          255        >19.8

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.204 in the direction of the burst (Schlegel et al. 1998).