TITLE:   GCN CIRCULAR
NUMBER:  42863
SUBJECT: GRB 251126A: Swift/UVOT Detection
DATE:    25/11/27 14:51:12 GMT
FROM:    Alice Breeveld at MSSL-UCL <a.breeveld@ucl.ac.uk>

A.A. Breeveld (UCL-MSSL) and R. Caputo (GSFC) report on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 251126A 86s after the BAT trigger (Caputo et al., GCN Circ. 42843).
The fading optical afterglow (Swain et al., GCN 42844; Fu et al., GCN 42848; Reguitti et al., GCN 42849; Broens et al., GCN 42850; Angulo et al., GCN 42855; Pulido-Torres et al., GCN 42856; Gupta et al., GCN 42857; Cotter et al., GCN 42858; Seki et al., GCN 42859 and Volnova et al., GCN 42861) is clearly detected in the initial UVOT exposures.

The non detection in the U and UV filters is consistent with the redshift of z=3.5 found by Angulo et al., (GCN Circ. 42855).

Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposures and subsequent exposures are:

Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

white_FC            86          236          147          20.0 ± 0.1
white              579          772           39          20.3 ± 0.3
white              880         1377          186          20.5 ± 0.2
u_FC               299          548          246         >20.4
v                  629         1080           58          18.7 ± 0.3
b                 1159         1352           39          19.4 ± 0.3
uvw1               853         1467           35         >18.32
uvm2               653          847           39         >18.00
uvw2               778         1402           58         >18.70

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.063 in the direction of the burst (Schlegel et al. 1998).