TITLE: GCN CIRCULAR NUMBER: 39897 SUBJECT: GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations DATE: 25/03/28 06:11:29 GMT FROM: J.-G. Ducoin at CPPM <ducoin@cppm.in2p3.fr> Jean-Grégoire Ducoin (CPPM), Enrique Moreno Méndez (UNAM), Stéphane Basa (LAM), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the SVOM/ECLAIRs GRB 250327B (Bouchet et al. GCN Circ. 39888) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We observed from 2025-03-28 04:33 to 05:04 UTC (7.4 to 7.9 hours after the trigger) and obtained 11 minutes of exposure in the r filter at a mean observing time of T+7.6 hours. The data were coadded with custom software and analyzed with STDpipe (Karpov 2024) with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction. We detect the afterglow (Moskvitin et al. GCN Circ. 39889, Xin et al. GCN Circ. 39890, O’Neill et al. GCN Circ. 39891, Burrows et al. GCN Circ. 39892, Malesani et al. GCN Circ. 39893, Lian et al. GCN Circ. 39894, Page et al. GCN Circ. 39895, Shrestha et al. GCN Circ. 39896) with a magnitude of r = 20.01 +/- 0.02 Further observations are ongoing. We acknowledge the excellent support from the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and thank the COLIBRÍ and DDRAGO engineering teams View this GCN Circular online at https://gcn.nasa.gov/circulars/39897. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...