GRB 251206A

Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Jean-Luc Atteia (IRAP), Noémie Globus (UNAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Marius Brunet (IRAP) report:

We imaged the field of the SVOM GRB 251206A (Brunet et al., GCN Circ. 43031
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 ) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-12-09 04:39 to 0625 UTC (from 55.8 to 57.2 hours after the trigger) and obtained 80 minutes of simultaneous exposure in the r and z filters.

The data were reduced, coadded, and analyzed with the ASU pipeline. 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 inside the ECLAIRs uncertainty region (Brunet et al., GCN Circ. 43031
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 ) to the following 5-sigma limits:

r > 23.3
z > 22.3

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

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.

M. Brunet, J.-L. Atteia (IRAP), N. Dagoneau (CEA), report on behalf of the SVOM team:

The SVOM/ECLAIRs telescope detected a transient source, labelled GRB 251206A, starting at 2025-12-06T20:48:20.92 UTC (T0), through an offline search with the event-by-event data downloaded through the X-band ground station.

The burst was detected within several energy ranges and timescales. The best detection is obtained by the Image Trigger (IMT) with a signal-to-noise ratio of 8.5 within 4-20 keV over a time window of 20.48 seconds starting at T0-20.48s.

The lightcurve shows an asymmetric double-peaked structure, with a minor peak followed by a major peak, lasting around 20 s.

The localization of the source is RA, Dec = 1.843, -4.404 degrees:

RA (J2000) = 00h07m22.32s    
Dec (J2000) = -04d24m16.85s 

with a 90% C.L. radius of 10.9 arcmin (including systematic error of 6 arcmin added in quadrature).

We note that no bright catalogued X-ray sources are found in the error box.

The time-averaged spectrum from T0-20.48s to T0 in the energy range 5-120 keV is best fitted by a power law. The powerlaw index is -1.96 -0.15/+0.17. With this model, the total fluence in 4-120 keV is (3.56 +0.28/-0.57)e-7 erg/cm^2.

All quoted errors are at the 68% confidence level.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. ECLAIRs was developed jointly by APC, CEA, CNES, and IRAP.

The SVOM point of contact for this event  is : Marius Brunet : marius.brunet at irap.omp.eu

Please contact him by email if you require additional information regarding the SVOM follow-up of this burst.