TITLE: GCN CIRCULAR NUMBER: 40003 SUBJECT: GRB 250331C: Swift/UVOT Upper Limits DATE: 25/04/01 13:06:09 GMT FROM: Mike Siegel at PSU/Swift MOC mhs18@psu.edu
M. H. Siegel (PSU) and S. B. Cenko (GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250331C 140 s after the BAT trigger (Cenko et al., GCN Circ. 39959). No optical afterglow consistent with the XRT position (Beardmore et al., GCN Circ. 39977) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are:
Filter T_start(s) T_stop(s) Exp(s) Mag
white_FC 140 289 147 >21.1 u_FC 297 547 246 >19.9 white 140 1717 411 >22.3 v 628 1767 136 >19.1 b 553 1863 133 >20.1 u 297 1841 363 >20.1 w1 676 1817 136 >19.1 m2 652 1792 136 >19.8 w2 603 1743 136 >20.0
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.921 in the direction of the burst (Schlegel et al. 1998).
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