GCN 44547: GRB 260511B SVOM/C-GFT optical counterpart detection

C. Wu (NAOC), Z. Kang (CHO), L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC) ，O. Go-det, M. Brunet (IRAP), L. Zhang (IHEP), D. Kong (GXU)
report on behalf of the SVOM/C-GFT team:

We observed the field of  GRB 260511B (SVOM burst-id sb26051102) detected by SVOM/ECLAIRs (Godet et al., GCN 44543) with LATIOS on SVOM/C-GFT. Observations start-ed at   2026-05-11T11:29:37 UTC, ~0.48 hr after the trigger. 


An uncatalogued optical source compared to Pan-STARRS1 is detected in our images within the ECLAIRs  localization error circle. Its position is  R.A., Dec. 192.57345, 4.05512  degrees:

R.A. (J2000) = 12h50m17.63s       
Dec. (J2000) = +04d03m18.4s

with an uncertainty of ~0.5 arcsec. The magnitudes is  mag_r = 15.56 +/- 0.04 at 45.32 min post-trigger.

The photometry was calibrated against nearby Pan-STARRS1 stars  and no correction for Galactic dust extinction was applied. 

We propose that this source is the optical counterpart of GRB 260511B.  Further analyses are ongoing.

We thank the observation assistants Bo-Wen Li and Hong-Xv Xue at Jilin observatory for their excellent support.

The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching.