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), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Antonio de Ugarte Postigo (LAM), Boting Wang (YNAO, CAS), Yehao Chen (SWIFAR, YNU), and Wanjin Xie (NAOC) 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.