GRB 260802A / EP J223759.5+531421: SVOM/COLIBRI (FM-GFT) optical upper limit

ATel #17936; Antonio de Ugarte Postigo (LAM), Asuka Kuwata (UNAM), Stephane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Gregoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo Garcia-Garcia (UNAM), Ramandeep Gill (UNAM), Noemie Globus (UNAM), Marion Guelfand (CPPM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego Lopez-Camara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Mendez (UNAM), Margarita Pereyra (UNAM), Fredd Sanchez Alvarez (UNAM), Benjamin Schneider (LAM), Alan M. Watson (UNAM), Wenjin Xie(NAOC), and Runchao Chen (NJU)
on 2 Aug 2026; 11:36 UT
Credential Certification: Antonio de Ugarte Postigo (adeugartepostigo@gmail.com)

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We imaged the field of the SVOM GRB 260802A (Feng et al., GCN Circ. 45270) using the DDRAGO wide-field imager on the SVOM/COLIBRI (FM-GFT) telescope. We observed from 2026-08-02 09:26:49 to 10:36:51 UTC (from 0.0188 1.2025 hours after the trigger) and obtained 61 minutes of exposure in the z band. The data were reduced, coadded and analyzed with the ASU and CPPM COLIBRI pipelines. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the ECLAIRs source position (Feng et al., GCN Circ. 45270) down to the following 5-sigma limit: z > 22.6 We note that the ECLAIRs coordinates are coincident with the EP J223759.5+531421 magnetar (Rea et al. ATel 17870) and that inspection of the most precise localisation, provided by XMM (Coti Zelati et al. ATel 17909) also shows no new counterpart down to a 3-sigma limit of: z > 23.1 Further observations are ongoing. We thank the staff of the Observatorio Astronomico Nacional at Sierra de San Pedro Martir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRI 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 Astronomico Nacional on the Sierra de San Pedro Martir, Baja California, Mexico. This ATel has been reported in parallel through GCN 45272.