GRB 261108C

H. L. Li, Y. N. Ma, C. Wu, L. P. Xin, Y. L. Qiu, Z. H. Yao, J. R. Xu, L. J. Chen, X. H. Han, J. Wang, Y. Xu, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, J. S. Deng, J. Y. Wei (NAOC), J. T. Palmerio (CEA/Irfu), M. Gnaoui (IAP) report on behalf of the SVOM/VT team.

SVOM/VT performed observation with automatic slew on the field of GRB 261108C triggered by SVOM/ECLAIRs (sb26110812, Hamburg et al., GCN 46198
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 ). The observation started at 2026-11-08T21:22:32 UTC, 202 seconds post trigger in VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.
 
No credible uncatalogued candidates were identified in the stacked images within the MXT error box (Hamburg et al., GCN 46198
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 ), compared with the Legacy Survey, down to 21.5 mag (6.5σ) in AB magnitudes, at the mid-time of 8.0 minutes post trigger. The exposure time is 50*10 seconds for both channels. 

The observation is ongoing. We are waiting for more data to perform deeper analysis.

The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.

A. Saccardi(CEA/Irfu), Y.Y. Shi (GXU), D. Turpin (CEA/Irfu), S.J. Yin (GXU), C. Wu, L.P. Xin (NAOC), Y.X. Guan (GXU), R. Hamburg (USRA), M. Gnaoui (IAP) report on behalf of the SVOM mission team:


We observed the field of GRB 261108C (SVOM burst-id sb26110812) detected by SVOM (Hamburg et al., GCN 46198
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 ) with the LCO 1m telescope at South African Astronomical Observatory equipped with the Sinistro instrument.

Our observation started on 2026-11-08T21:23:19 UT (about 4.15 min after the trigger) and we obtained 3x200 s exposures in the SDSS r and Pan-STARRS z filter.

In the stacked image, we do not detect any new source within the SVOM/ECLAIRs error box. We measure the following upper limits calibrated against the DESI Legacy Imaging Surveys DR10 catalog, and not corrected for Galactic extinction:

r > 22.1 AB (5-sigma, mid-time 27.10 min after the trigger),
z > 19.9 AB (5-sigma, mid-time 9.58 min after the trigger).

This project is funded by the SVOM collaboration.

R. Hamburg (USRA), M. Gnaoui (IAP), C. Lachaud (APC), and A. Coleiro (APC) report on behalf of the SVOM mission team:

At 2026-11-08T21:19:10 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 261108C (SVOM burst-id sb26110812).

The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 8 alerts. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 13.48 in the [5-20] keV energy band over a time window of 40.96 seconds starting at 2026-11-08T21:18:34.

The localization of the best alert is R.A., Dec. 11.7202, -64.2564 degrees (J2000) with a 90% confidence level (C.L.) radius of 6.05 arcmin (including systematic error of 2 arcmin added in quadrature).

The SVOM/ECLAIRs light curve showed a broad structure with a T90 duration of about 140 s.

SVOM slewed to the burst.

SVOM/MXT began observing the field at 2026-11-08T21:21:21 UTC, 131 seconds after T0. Using onboard processed data we found an uncatalogued X-ray source located at R.A., Dec. 11.7459, -64.2949 degrees:
R.A. (J2000) = 0h46m59.02s
Dec. (J2000) = -64d17m41.51s
with a 90% C.L. radius of 76.22 arcseconds.

This location is 2.40 arcminutes from the ECLAIRs onboard position. This position may be improved as more data is received.

VT began observing the field after the slew. The analysis of the data will be published in a future circular.

The Space-based multi-band astronomical 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. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE.

The Burst Advocate (BA) on shift for this alert is M. Gnaoui: mouad.gnaoui@sorbonne-universite.fr. Please contact the BA by email if you require additional information.