TITLE: GCN CIRCULAR NUMBER: 41449 SUBJECT: GRB 250813B: Swift/UVOT Upper Limit DATE: 25/08/20 15:17:24 GMT FROM: Mike Siegel at PSU/Swift MOC mhs18@psu.edu

M. H. Siegel (PSU) reports on behalf of the Swift/UVOT team:

The Swift/UVOT began settled observations of the field of GRB 250813B 9.6 ks after the SVOM/ECLAIRs trigger (Xie et al., GCN Circ. 41352). We do not detect any afterglow consistent with the XRT position (Page et al., GCN Circ. 41359) or optical position (Jelinek et al., GCN Circ. 41355).

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 9599 16347 1576 >21.07

The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.072 in the direction of the burst (Schlegel et al. 1998).

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