TITLE:   GCN CIRCULAR
NUMBER:  45607
SUBJECT: GRB 260917B: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
DATE:    26/09/17 08:10:04 GMT
FROM:    damien dornic <damiendornic@gmail.com>

Damien Dornic (CPPM), Margarita Pereyra (UNAM), Benjamin Schneider (LAM), Stéphane 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), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García-García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Fredd Sánchez Álvarez (UNAM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Hanrui He (PMO), and Wenjin Xie (NAOC) report:

We imaged the field of the SVOM GRB 260917B (He et al., GCN Circ. 45606) using the DDRAGO two-channel wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2026-09-17 05:24:09 to 2026-09-17 05:33:40 UTC (from 1.53 to 1.69 hours after the trigger) and obtained 16 minutes of simultaneous exposure in the r/z filters.

The data were reduced, coadded and analyzed with the COLIBRÍ pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1, is in the AB system, and is not corrected for Galactic extinction.

We detect an uncatalogued and fading source consistent with the ECLAIRs 8.84 arcmin error circle (He et al., GCN Circ. 45606) at: 

RA(J2000) = 03:07:56.12 = 46.98383 degrees
Dec(J2000) = +25:33:24.4 = 25.55678 degrees
with an uncertainty of 0.5 arcsec.

The preliminary magnitude derived for that source is:

r = 21.29 +/- 0.06
z = 19.84 +/- 0.06

Further observations are ongoing.

We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM.

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.