TITLE: GCN CIRCULAR NUMBER: 40048 SUBJECT: GRB 250403A: Swift/UVOT Detection DATE: 25/04/04 13:28:59 GMT FROM: Sam Shilling at Lancaster University shilling.sam@gmail.com
S. P. R. Shilling (Lancaster U.), S. R. Oates (Lancaster U.) and S. Dichiara (PSU) report on behalf of the Swift UVOT team:
Swift/UVOT observed the field of GRB 250403A detected by Fermi GBM (Fermi team, GCN Circ. 40025) and SVOM/ECLAIRs (Julakanti et al., GCN Circ. 40026), starting at 17:22:59 UT on 24/04/03, ~2.1 hours after the initial detections.
An optical afterglow is initially detected in the U-band consistent with the position of the uncatalogued X-ray source detected by Swift/XRT (Dichiara et al., GCN Circ. 40037) and the optical afterglow detected by various facilities (Starling et al., GCN Circ. 40028; Wu et al., GCN Circ. 40029; Du et al., GCN Circ. 40031; Li et al., GCN Circ. 40032; Ghosh et al., GCN Circ. 40039; Jiang et al., GCN Circ. 40041; Pérez-Fournon et al., GCN Circ. 40043; Xin et al., GCN Circ. 40045). At 00:02:02 UT on 25/04/04, ~6.7 hours later, the optical afterglow is no longer detected.
The preliminary detection and 3-sigma upper limits calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial and subsequent exposures are:
Filter T_start(h) Exp(s) Mag
u 2.1 396 19.2 +/- 0.2 u 8.8 492 >20.3 b 8.8 386 >20.5 v 9.0 130 >19.0 w1 12.1 164 >19.3 m2 12.0 245 >19.7 w2 8.9 246 >19.8
The magnitudes given are calculated using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) and are not corrected for the Galactic extinction.
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