TITLE: GCN CIRCULAR NUMBER: 40183 SUBJECT: GRB 250419A: LCO optical afterglow multi-band observations DATE: 25/04/20 11:35:44 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es> I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, A.E. Hernández-Díaz, I. Correa-Plasencia (ULL), and A. López-Oramas (IAC and ULL) Following the detection of the Gamma-Ray Burst GRB 250419A by SVOM/ECLAIRs (Wang et al., GCN circ. 40168) and of the X-ray afterglow by Swift-XRT (Page et al., GCN circ. 40173), we observed the GRB field with the two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Siding Spring Observatory (Australia) in the SDSS u, g, r, and i filters. The observations started at 2025-04-19 11:20:00 UTC, about 8.84 hours after the SVOM trigger, with simultaneous observations in the r and i filters followed by simultaneous observations in the u and g filters. An uncatalogued source is detected in the four filters at the position of the optical afterglow reported first by Ocelotl López et al. (GCN circ. 40169), that is consistent with the Swift-XRT position (Page et al., GCN circ. 40176) and with other optical detections reported by Xin et al. (GCN circ. 40170), Zheng et al. (GCN circ. 40171), Kumar et al. (GCN circ. 40172), Thakur et al. (GRB redshift of z = 0.845, GCN circ. 40174), Lipunov et al. (GCN circ. 40179), Odeh et al. (GCN circ. 40180), Perley and Bochenek (GCN circ. 40181), and Pankov et al. (GCN circ. 40182). We measure the following magnitudes, calibrated against SDSS DR16 (Ahumada et al. 2020, ApJS, 249, 3A) stars, that are not corrected for Galactic extinction: Date | UT start | mag | error | filter | exposure time (sec) | ------------------------------------------------------------------------ 2025-04-19 11:20:00 19.15 0.07 i 300 2025-04-19 11:20:03 19.40 0.06 r 300 2025-04-19 11:45:15 20.13 0.17 u 300 2025-04-19 11:45:32 19.76 0.09 g 300 This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF). View this GCN Circular online at https://gcn.nasa.gov/circulars/40183. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...