TITLE:   GCN CIRCULAR
NUMBER:  41017
SUBJECT: GRB 250704A: SVOM/COLIBRÍ (FM-GFT) optical observations
DATE:    25/07/07 19:33:31 GMT
FROM:    Benjamin Schneider at MIT <bschn@mit.edu>

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

We imaged the field of the SVOM GRB 250704A (Cao et al., GCN Circ. 40934) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-07-05 10:03:36 to 10:45:54 UTC (from 1.26 to 1.29 days after the trigger) and obtained 32 minutes of exposure in the r filter.

The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction.

We detected the optical counterpart reported by Schneider et al., GCN Circ. 40953; Cao et al., GCN Circ 40964; and Siegel et al., GCN 40981 at a preliminary magnitude of:

r = 22.05 +/- 0.09

Further observations are planned.

We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.

COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.