TITLE: GCN CIRCULAR NUMBER: 39945 SUBJECT: GRB 250329B: SVOM/COLIBRÍ (F-GFT) optical upper limit DATE: 25/03/30 15:32:15 GMT FROM: J.-G. Ducoin at CPPM ducoin@cppm.in2p3.fr

Ny Avo Rakotondrainibe (LAM), Jean-Grégoire Ducoin (CPPM), Jean-Luc Atteia (IRAP), Margarita Pereyra (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), 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), Enrique Moreno Méndez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM) report:

We imaged the field of GRB 250329B detected by SVOM/ECLAIRs as trigger sb25032902, (Xie et al., GCN Circ. 39925) 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 observed from 2025-03-30 04:04 to 05:50 UTC (15.9 to 17.66 hours after the trigger) and obtained 80 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.

At the XRT localization (Beardmore et al., GCN Circ. 39939), we do not find any optical counterpart to a 3-sigma limiting magnitude of:

i > 23.73.

Our result is consistent with previous optical non-detections (Xie et al., GCN Circ. 39926; Chen et al., GCN Circ. 39929; Xin et al., GCN Circ. 39931; and Wu et al., GCN Circ 39935)

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

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