GCN Circular 46211

Michael C. Davis (UMN), Tomas Ahumada (NOIRLab), and Michael Coughlin (UMN) report:

We observed the field of GRB 261108D, detected by SVOM/ECLAIRs (Zhang et al., GCN 46200

), with the Dark Energy Camera (DECam) on the 4-m Blanco telescope at CTIO. Observations began on 2026-11-09 at 07:52:29 UTC (approximately 8.00 hours after the trigger) under program 2026B-398365 (PI Davis).

Observations consisted of 1x300 s exposures in each of the r and i bands. The images were reduced with the NOIRLab DECam Community Pipeline (Valdes et al. 2014). After performing PSF-matched image subtraction against pre-burst Legacy Surveys DR11 coadds (Dey et al. 2019), we detect the candidate counterpart reported by Passaleva et al., GCN 46210

. Our difference-image position, RA, Dec (J2000) = 170.604125 deg, Dec = -77.631611 deg, is about 0.3" from the near-infrared position. Photometry is calibrated against Legacy Surveys DR11 field stars.

We measure the following AB magnitudes, not corrected for Galactic extinction:

Start UT	T_mid - T0	Filter	Exposure	Magnitude (AB)
2026-11-09T07:52:29	0.3350	r	1x300s	22.13 ± 0.09
2026-11-09T07:57:59	0.3388	i	1x300s	21.56 ± 0.11

We encourage further monitoring to establish the source’s relationship to the burst.

We thank the CTIO and NOIRLab staff for their support during these observations.