GCN Circular 45952
Subject
GRB 261010A: LBT tentative near-infrared detection
Event
Date
2026-10-15T14:40:26Z (an hour ago)
From
Andrea Rossi at INAF <andrea.rossi@inaf.it>
Via
Web form
E. J. Marchesini, A. Rossi (INAF-OAS), R. Brivio, P. D’Avanzo (INAF-OAB), A. Melandri (INAF-OAR), L. Izzo (INAF-OACN and DARK/NBI), G. Stratta (INAF-OAS), R. Maccary, M. Bulla (University of Ferrara) on behalf of the GRAWITA collaboration, and D. B. Malesani (DAWN/NBI and Radboud) report:
We observed the field of GRB 261010A detected by Fermi/GBM (Fermi GBM team, GCN 45888), Swift (Lien et al., GCN 45889), and Konus-Wind (Frederiks et al., GCN 45925), in H band with the LUCI1 and LUCI2 near-infrared imager and spectrograph mounted on the Large Binocular Telescope (LBT, Mt Graham, AZ, USA). Observations were obtained on 2026-20-15 at the midtime UT 01:56:00, i.e. ~4.3 days after the GRB trigger, for a total of 62 min of on-source under very good sky conditions.
At the position of the afterglow (O’Neill et al., GCN 45890; Aceituno et al., GCN 45891; Corcoran et al., GCN 45912) we tentatively detect a faint flux excess at H = 24.0 ± 0.3 AB mag, close to our detection limit. The photometry was calibrated against 2MASS field stars.
Two possible associations have been pointed out for this GRB: with the nearby galaxy LEDA 1781464 at z = 0.07 (Corcoran et al., GCN 45912) and with a red object at z = 0.785 (Castro-Tirado et al., GCN 45928). A kilonova at redshift 0.07 would be about 1 mag brighter than our detection. For example, the KN associated with GRB 211211A at z = 0.076 reached J ~ 23 and K ~ 22.5 AB at a comparable epoch (Rastinejad et al. 2022, Nature 612, 223). Similarly, with a corresponding absolute magnitude of approximately M_H ~ −14 (AB), the tentative detection would be about 1 mag fainter than the kilonova AT 2017gfo, which had an absolute magnitude of approximately M_H ~ −15 (AB) at 5 days after the merger (Villar et al. 2017 ApJL 851 L21).
While the light curve of this transient is not well constrained, the observed emission is possibly due to the GRB afterglow at z = 0.785, or in principle even to an underlying, previously undetected host galaxy or host galaxy region. Further observations are needed to establish the nature of this faint source.
We acknowledge the excellent support from the LBTO and LBT-INAF staff, particularly J. Rupert and F. Cusano, in obtaining these observations.