TITLE: GCN CIRCULAR NUMBER: 39814 SUBJECT: GRB 250321A: Swift/UVOT Upper Limits DATE: 25/03/21 13:55:16 GMT FROM: Sam Shilling at Lancaster University shilling.sam@gmail.com
S. P. R. Shilling (Lancaster U.) and R. Gupta (NASA/GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 250321A 128 s after the BAT trigger (Gupta et al., GCN Circ. 39794). No optical afterglow consistent with the XRT position (Page et al., GCN Circ. 39798) 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 128 278 147 >19.9 white 128 4071 344 >20.6 v 4282 4482 197 >18.9 b 3667 5142 236 >20.0 u 340 5097 232 >19.4 w1 4693 4892 197 >19.3 m2 4487 4687 197 >19.2 w2 4077 4277 197 >19.3
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 4.368 in the direction of the burst (Schlegel et al. 1998).
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