GCN Circular 45952
GRB 261010A: LBT tentative near-infrared detection
From: Andrea Rossi at INAF
Issued: 2026-10-15 14:40 UTC
Type: GRB
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.
Every one of the gamma-ray bursts GCN reports is posted here.
Relayed automatically from NASA's General Coordinates Network.
Transient Alerts » in reply to GRB 261010A
In plain words Notable
On 10 October 2026 several gamma-ray satellites (Fermi, Swift, Konus-Wind and others) recorded a burst of gamma rays in the constellation Hercules that lasted about a minute. Swift's X-ray telescope and ground telescopes quickly found a fading X-ray and optical afterglow, which confirms the position. The host galaxy is uncertain: it is either a nearby galaxy about 25 arcseconds away at redshift 0.070, or a fainter galaxy 2 arcseconds away at redshift 0.785, meaning the light left roughly 7 billion years ago. Several teams say the burst's flash pattern and energy look more like those of a merger of two compact stars (such as neutron stars) than the collapse of a massive star, even though the burst was long. No kilonova (the glow from freshly made heavy elements after a merger) has been seen, and radio searches found nothing; the deep, late near-infrared images are too shallow to rule one out.
How unusual is it? A long gamma-ray burst with an optical afterglow, a measured redshift, and several independent analyses pointing to a merger origin is out of the ordinary, but no kilonova has been seen and the host is unconfirmed. It would become exceptional if a kilonova were confirmed, and would drop back toward routine if the burst were shown to come from a collapsing massive star.
Written by an AI model (claude-sonnet-5-5) from the official reports in this thread, and rewritten as new reports arrived (version 9); last updated . It may contain mistakes: the reports themselves are the authority.
GRB 261010A: LBT tentative near-infrared detection
The whole thread (25 posts)
- GRB 261010A
- GRB261010A: Retraction of Keck/MOSFIRE near-IR source
- GRB 261010A: Pan-STARRS z-band imaging and upper limit
- GRB 261010A: VLA radio observations
- GRB261010A: Keck/MOSFIRE detection of a near-IR source
- GRB 261010A: ASKAP non-detection of a radio afterglow
- GRB 261010A: LBT tentative near-infrared detection
- GRB 261010A: Glowbug gamma-ray detection
- GRB 261010A: initial pulse rest-frame energetics from Konus-Wind detection
- GRB 261010A: a short minimum variability timescale and a distinct pulse evolution compatible with a merger origin
- GRID detection of GRB 261010A
- GRB 261010A: J-band upper limit by the SYSU 80cm infrared telescope
- GRB 261010A: Swift-XRT refined Analysis
- GRB 261010A: a Type I-L (merger-driven) GRB candidate
- Updated explainer: what the latest reports add (AI-written)
- GRB 261010A: 10.4m GTC spectroscopy of the galaxy 2" from the afterglow
- Konus-Wind detection of GRB 261010A
- GRB 261010A: Swift-BAT refined analysis
- GRB 261010A: NOT confirmation of the optical afterglow
- GRB 261010A: Fermi GBM Observation
- Explainer: what this is and why it matters (AI-written)
- GRB 261010A: Enhanced Swift-XRT position
- GRB 261010A: possible optical afterglow detected with the 1.5m OSN
- GRB 261010A: NOT possible optical counterpart
- GRB 261010A: Swift detection of a burst