GCN Circular 45912
Subject
GRB 261010A: NOT confirmation of the optical afterglow
Event
Date
2026-10-11T22:16:41Z (2 days ago)
From
Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
G. Corcoran (UCD), D. B. Malesani (DAWN/NBI and Radboud), D. O’Neill (Birmingham), L. Izzo (INAF/OAC and DARK/NBI), B. P. Gompertz (Birmingham), A. Martin-Carrillo (UCD), A. Schenone-Zanuzzi (NOT), E. Georgiou (NOT and Turku Univ.) report on behalf of a larger collaboration:
We observed again the position of the Swift and Fermi GRB 261010A (Lien et al., GCN 45889; Palafox & Jameson, GCN 45911) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. A total of 6x300 s were secured in the SDSS r band, with a mean epoch 2026 Oct 11.85154 UT (25.152 hr after trigger).
The candidate optical counterpart (O’Neill et al., GCN 45890; Aceituno et al., GCN 45891) is no longer detected in our images. Performing image subtraction using the Legacy survey as template, we measure a limiting magnitude r > 23.9 (AB; calibrated against nearby Pan-STARRS objects, and not corrected for Galactic extinction).
We also note that the refined Swift/XRT position (Osborne et al., GCN 45894) has slightly shifted compared to the promptly-released coordinates (Lien et al., GCN 45889), and is now fully consistent with the location of the optical counterpart candidate. We thus conclude that this object is indeed the afterglow of GRB 261010A.
The position of the afterglow is about 25" (34.5 kpc in projection) away from the nearby galaxy LEDA 1781464 at redshift z = 0.070. The chance association probability is of order 1% (comparable to that for the fainter, redder object 2" away from the afterglow; O’Neill et al., GCN 45890). We note that, if placed at z = 0.070, our limit implies a luminosity > 1.5 mag fainter than AT 2017gfo at a comparable phase (e.g. Villar et al. 2017, doi:10.3847/2041-8213/aa9c84).