TITLE: GCN CIRCULAR NUMBER: 39915 SUBJECT: GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate DATE: 25/03/29 05:20:22 GMT FROM: Alan Watson at UNAM alan@astro.unam.mx
Alan M. Watson (UNAM), Ramandeep Gill (UNAM), Sarah Antier (OCA/IJCLAB), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Francesco Magnani (CPPM), Diego López-Cámara (UNAM), Benjamin Schneider (LAM), Dalya Akl (AUS), Camila Angulo (UNAM), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (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 imaged the field of the SVOM/ECLAIRs GRB 250329A (sb25032901) with the DDRAGO wide-field imager on the SVOM/COLIBRÍ (F-GFT) telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We observed from 2025-03-29 04:18 to 04:55 UTC (55 to 2256 seconds after the trigger) and obtained 26 minutes of exposure in the i filter. The data were coadded with custom software and analyzed in STDWeb/STDPipe (Karpov 2024), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction.
Within the SVOM/ECLAIRs error box, we detect a bright uncatalogued source at RA = 197.44679 and Dec = 9.49533 (J2000) with a magnitude of
i = 17.91 +/- 0.03
Further observations are planned.
We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
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