TITLE: GCN CIRCULAR NUMBER: 39920 SUBJECT: GRB 250328A: SVOM/COLIBRÍ (F-GFT) optical afterglow candidate DATE: 25/03/29 11:09:27 GMT FROM: COLIBRI at COLIBRI Consortium <gcn@colibri-obs.org> Benjamin Schneider (LAM), Jean-Grégoire Ducoin (CPPM), Sarah Antier (OCA/IJCLAB), Ramandeep Gill (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Francesco Magnani (CPPM), Diego López-Cámara (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Antonio de Ugarte Postigo (LAM) report: We observed the field of the SVOM/ECLAIRs GRB 250328A (Brunet et al., GCN 39910) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (F-GFT) telescope. We obtained 50 min of exposures in the i-band starting at 06:57:58 UT on 2025-03-29 (14.0 hr after the SVOM trigger). In the stacked image, we detect a source at the near-infrared afterglow candidate position reported by Schneider et al., GCN 39919 and consistent with the XRT source #2. At that position, no source is visible either in the PanSTARRS survey or the Legacy Survey. The preliminary magnitude derived for that source is i = 22.04 +/- 0.24 mag (AB). The data were coadded with the Colibri pipeline and analyzed with STDWeb/STDPipe (Karpov 2021). The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitude is not corrected for Galactic extinction. Further observations are ongoing. We acknowledge the excellent support from the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir. View this GCN Circular online at https://gcn.nasa.gov/circulars/39920. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...