{
  "circularId": 40023,
  "version": 2,
  "submittedHow": "web",
  "submitter": "Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com>",
  "body": "Francesco Magnani (CPPM), Camila Angulo (UNAM), Damien Dornic (CPPM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), , Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and X. Chen (YNU) report:\n\nWe imaged the field of the SVOM/ECLAIRs GRB 250402A (sb25040203, Chen et al. GCN 40014) with the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.\n\nWe observed from 2025-04-03 04:37 to 06:49 UTC (between 5.49 and 7.69 hours after the trigger) and obtained 43 minutes of exposure in the i filter. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction.\n\nAt the position of the previously reported optical afterglow (Xin et al., GCN 40015; Pérez-Fournon et al. GCN 40020; Schneider et al. GCN 40022), we detect a source with a magnitude of\n\ni = 21.22 +/- 0.11 \n\nFurther observations are ongoing.\n\nWe warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.\n",
  "format": "text/plain",
  "editedBy": "Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Francesco Magnani at Aix-Marseille Université, CPPM/CNRS <francesco.magnani.work@gmail.com>",
  "bibcode": "2025GCN.40023....1M",
  "createdOn": 1743677319282,
  "subject": "GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart",
  "eventId": "GRB 250402A",
  "editedOn": 1743774065938
}