TITLE: GCN CIRCULAR NUMBER: 40148 SUBJECT: SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart DATE: 25/04/16 09:50:29 GMT FROM: F. Fortin at IRAP ffortin.sci.edu@gmail.com

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

We observed the field of SVOM/ECLAIRs sb25041603 (Wang et al. GCN 40147) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope operated from the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico. We obtained 50 exposures of 60 s in the i-band starting at 06:39:55 UT on 2025-04-16 (12 min after the onboard trigger, and 16 s after the alert reception).

In the stacked image, we do not detect any new source at the ECLAIRs source position (Wang et al. GCN 40147) down to the following 5-sigma limit:

i > 22.89 mag (AB)

The data were coadded with the Colibrí pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometric calibration was performed using nearby stars from the PanSTARRS DR1 catalog and the magnitude is not corrected for Galactic extinction.

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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