GCN 44061: GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening

Malte Busmann, Ziyuan Zhu, Mitra Maleki (LMU), Julius Gassert (LMU/CMU), Daniel Gruen (LMU), Xander J. Hall, Brendan O'Connor, Antonella Palmese (CMU) report:

We observed the optical/NIR counterpart of GRB 260310A (Fermi GBM team, GCN 43951; Salunke et al., GCN 43958), AT 2026fgk (e.g. O'Neill et al. 2026, TNS Discovery Report 294132; Konno et al., GCN 43974; Hinds et al., GCN 43977), with the Three Channel Imager (3KK) at the Fraunhofer Telescope at Wendelstein Observatory (FTW) in the g, r, i, z, J, and Ks band starting at 2026-03-19T23:22:38 (9.77 days after the GRB trigger) and 2026-03-20T22:36:22 (10.74 after the GRB trigger). Unlike suggested by Becerra et al. (CGN 44059) we do not see signs of rebrightening in our observations in any filter (see also Volnova et al., GCN 44060). 

We thank Michael Schmidt and Silona Wilke for obtaining these observations.