TITLE: GCN CIRCULAR NUMBER: 40185 SUBJECT: GRB 250409A: Swift/UVOT Follow up DATE: 25/04/20 12:39:57 GMT FROM: Paul Kuin at MSSL npkuin@gmail.com
Paul Kuin (MSSL/UCL) reports on behalf of the Swift/UVOT team:
The Swift/UVOT began observations of the field of SVOM detected GRB 250419A/(SVOM burst-id sb25041901) 3790s after the SVOM ECLAIR trigger at 2025-04-19T02:29:32 (Wang et al., GCN Circ. 40168). A source consistent with the position reported by Kin Ocelotl López et al. (Colibri - GCN Circ. 40169) and Liping Xin at al. (SVOM-VT GCN Circ 40170), also reported by Weikang Zheng et al. (KAIT - GCN Circ. 40171) and Amit Kumar et al. (GCN Circ. 40172) has been detected in the initial UVOT exposures.
The detections using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are:
Filter T_start(s) Exp(s) Mag (Vega)
u 3790 1667 17.73 +/- 0.04 u 9323 259 18.19 +/- 0.10 u 48658 1206 19.64 +/- 0.14 u 54296 1028 19.52 +/- 0.13
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.085 in the direction of the burst (Schlegel et al. 1998).
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