TITLE:   GCN CIRCULAR
NUMBER:  44959
SUBJECT: GRB 260610B / AT 2026owq: Liverpool Telescope confirmation of continuing optical rebrightening
DATE:    26/06/16 20:04:25 GMT
FROM:    Dimple  at University of Birmingham <dimplepanchal96@gmail.com>

Dimple (U. Birmingham), B. P. Gompertz (U. Birmingham), A. Bochenek (LJMU), D. A. Perley (LJMU), D. O’Neill (U. Birmingham), D. B. Malesani (DAWN/NBI and Radboud) and A. Martin-Carrillo (UCD) report on behalf of a larger collaboration:

We have conducted nightly griz observations of the optical afterglow (O’Neill et al., GCNs 44903, 44914; Watson et al., GCN 44905; Zhu et al., GCN 44909; Gillanders et al., GCNs 44910, 44955; Akl et al., GCNs 44911, 44930; Moskvitin et al., GCNs 44918, 44929; Jackson-Horne et al., GCN 44919; Izzo et al., GCN 44920; Li et al., GCN 44921; Bochenek et al., GCNs 44927, 44932; Pankov et al., GCN 44946; Angulo et al., GCN 44958) of GRB 260610B (Fermi GBM Team, GCN 44901; Yu et al., GCN 44944) with the IO:O optical camera on the 2m robotic Liverpool Telescope.

In our two most recent epochs we detect the optical rebrightening first suggested by Gillanders et al. between their t-t0 = 3.3 and 4.3 day epochs (GCN 44955) in all filters. The measured g- and r-band AB magnitudes are:

|  t-t0(d)  |  filter  |  mag  |
|  3.99  |  g  |  21.71 ± 0.07  |
|  3.97  |  r  |  21.34 ± 0.07  |
|  5.08  |  g  |  21.49 ± 0.08  |
|  5.09  |  r  |  21.02 ± 0.07  |

These observations indicate that GRB 260610B continues experiencing a rebrightening episode beyond 5 days after trigger. We detect no change in g-r colour when comparing our observations to the earliest Liverpool Telescope epoch (Bochenek & Perley, GCN 44927), suggesting an achromatic rebrightening, inconsistent with expectations for an emerging supernova.

The above magnitudes are calibrated against nearby Pan-STARRS objects and are not corrected for Galactic extinction.