TITLE: GCN CIRCULAR NUMBER: 40315 SUBJECT: GRB 250205A: 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 250205A (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.

View this GCN Circular online at https://gcn.nasa.gov/circulars/40315. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...