TITLE:   GCN CIRCULAR
NUMBER:  40359
SUBJECT: GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
DATE:    25/05/06 04:50:55 GMT
FROM:    Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com>

Antonio de Ugarte Postigo (LAM), William H. Lee (UNAM), Sarah Antier (OCA), Stéphane Basa (UAR Pytheas), Alan M. Watson (UNAM); 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), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), and Chenw ei Wang (IHEP) report:

We imaged the field of GRB 250506A (Wang et al. GCN 40358) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.

We started observations at 2025-05-06 03:29:48 (1.106 hours after the trigger). An initial stack with 16 minutes of exposure in the i filter was obtained with a mean epoch 1.266 hrs after the burst. The data were coadded with the COLIBRÍ pipeline and analyzed in STDWeb/STDPipe (Karpov 2025), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is in the AB system and is not corrected for Galactic extinction.

No credible counterpart is detected down to an AB 5-sigma limit of i > 22.2 mag.

Further observations are ongoing.

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