TITLE: GCN CIRCULAR NUMBER: 39930 SUBJECT: GRB 250327B: SVOM/COLIBRÍ (F-GFT) Further Observations DATE: 25/03/29 19:02:34 GMT FROM: Alan Watson at UNAM <alan@astro.unam.mx> Jean-Grégoire Ducoin (CPPM), Noémie Globus (UNAM), Camila Angulo (UNAM), Sarah Antier (OCA), Ramandeep Gill (UNAM), Stéphane Basa (LAM), William H. Lee (UNAM), Dalya Akl (AUS), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Hui Yang (IRAP) report: We observed the field of 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 obtained 50 minutes of exposure in the i filter from 2025-03-29 03:49 and 11:32 (44.3 and 52.0 hours after the trigger). Our observations were not continuous, but rather were at the start and end of this interval with a long interruption for observations of other sources. We observed through thick clouds. The data were coadded with the COLIBRI pipeline and analysed in STDWeb/STDPipe (Karpov 2021). The photometric calibration was performed using nearby stars from the Pan-STARRS DR1 catalog and the magnitude is not corrected for Galactic extinction. At the position of the previously reported optical transient (Moskvitin et al., GCN Circ. 39889; Xin et al., GCN Circ. 39890; O’Neill et al., GCN Circ. 39891; Malesani et al., GCN Circ. 39893; Lian et al., GCN Circ. 39894; Page et al., GCN Circ. 39895; Shrestha et al., GCN Circ. 39896; Perley & Bochenek, GCN Circ. 39902; Kumar et al., GCN Circ. 39904; Dennefeld et al., GCN Circ. 39905; Pankov et al., GCN Circ. 39906; Pérez-Fournon et al., GCN Circ. 39912; Tarasenkov et al., GCN Circ. 39913; Mo et al., GCN Circ. 39914), we detect a source with i = 22.23 +/- 0.15. Compared to our previous observation at about 7.65 hours after the trigger, the temporal decay index is about -1.0. We acknowledge the excellent support of 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/39930. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...