GCN Circular 40002
Subject
GRB 250331B: Swift/UVOT Upper Limits
Date
2025-04-01T13:04:29Z (3 days ago)
From
Mike Siegel at PSU/Swift MOC <mhs18@psu.edu>
Via
Web form
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 250331B
317 s after the BAT trigger (Cenko et al., GCN Circ. 39958).
No optical afterglow consistent with the XRT position (Osborne et al., GCN
Circ. 39974) 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 317 467 147 >19.5
white 317 1020 334 >19.9
v 474 1070 78 >18.3
b 572 764 39 >18.3
u 547 1144 58 >18.6
w1 523 1120 58 >18.0
m2 670 690 19 >17.7
w2 621 1046 58 >18.4
The magnitudes in the table are not corrected for the Galactic extinction
due to the reddening of E(B-V) = 0.979 in the direction of the burst
(Schlegel et al. 1998).