TITLE: GCN CIRCULAR NUMBER: 39784 SUBJECT: GRB 250317B: SVOM/COLIBRI (F-GFT) follow-up observations DATE: 25/03/19 17:09:35 GMT FROM: Jean-Luc Atteia at IRAP jean-luc.atteia@irap.omp.eu
Jean-Luc Atteia (IRAP), Sarah Antier (OCA/IJCLAB), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Antonio de Ugarte Postigo (LAM), Benjamin Schneider (LAM) report:
We imaged the field of the SVOM/ECLAIRs GRB 250317B (Zhao et al. GCN Circ. 39752, Zhao et al. GCN Circ. 39753) with the DDRAGO imager on the COLIBRÍ (SVOM/F-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We observed from 2025-03-19 06:32 to 11:00 UTC and obtained 200 minutes of exposure in the r filter at a mean observing time To+54.5h. 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 optical afterglow (Watson et al. GCN Circ. 39754, Pérez-Fournon et al. GCN Circ. 39757, Ghosh et al. GCN Circ. 39759, Ferro et al. GCN Circ. 39764, Schneider et al. GCN Circ. 39767, Schneider et al. GCN Circ. 39767, Thoene et al. GCN Circ. 39769, Zhu et al. GCN Circ. 39770, Zhu et al. GCN Circ. 39770, Pankov et al. GCN Circ. 39772, Moretti et al. GCN Circ. 39774, Schneider et al. GCN Circ. 39777) with a magnitude of
r = 23.95 +/- 0.25
This confirms the break of the optical light-curve pointed by Schneider et al. in GCN Circ. 39777.
We acknowledge excellent support from the staff of the Observatorio Astronómico Nacional.
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