TITLE:   GCN CIRCULAR
NUMBER:  40315
SUBJECT: GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
DATE:    25/05/02 10:25:06 GMT
FROM:    Ny Avo Rakotondrainibe at LAM <nyavo.rakotobe@gmail.com>

Ny Avo Rakotondrainibe (LAM), Enrique Moreno Méndez (UNAM), Jean-Grégoire Ducoin (CPPM), Benjamin Schneider (LAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Antonio de Ugarte Postigo (LAM) and Y. Wang (PMO, CAS) report:

We imaged the field of the SVOM/ECLAIRs GRB 250502A (sb25050205) 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.

We observed from 2025-05-02 08:58 UTC to 09:17 UTC (682 to 1848 seconds after the trigger) and obtained 16 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.
Within the SVOM/ECLAIRs error box, we detect a bright uncatalogued source at:

RA (J2000) = 13:46:05.60 = 206.5233d
Dec (J2000) = -10:45:31.9 = -10.7588d

The preliminary magnitude derived for that source is:

i = 17.41 +/- 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.