GCN Circular 45818
GRB 261005B: J-band upper limit with WINTER
From: unknown
Issued: 2026-10-06 11:46 UTC
Type: GRB
Tanishk Mohan (IITB), Geoffrey Mo (Caltech/Carnegie), Viraj Karambelkar (Columbia), Benjamin Schneider (LAM), Tomas Ahumada (NOIRLab), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of GRB 261005B (Parsotan et al., GCN 45812; Godwin et al., GCN 45816) in the near-infrared J band with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations began on 2026-10-06 at 02:30:42.092 UTC in the J band (4.86 hr after the BAT trigger), consisting of 15*120 sec exposures. The images were processed using the WINTER data reduction pipeline implemented with mirar (GitHub - winter-telescope/mirar: Modular Image Reduction and Analysis Resource (MIRAR) (github.com), winter-telescope/mirar: v0.17.0 (doi.org)).
We do not detect any new source at the enhanced Swift-XRT position (Page at al., GCN 45815).
We obtain the following 5-sigma upper limit: J = 19.17 mag (AB).
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
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 261005B
In plain words Routine
On the evening of 5 October 2026 (UTC), two space telescopes, NASA's Swift and Fermi, both caught a burst of gamma rays (the most energetic form of light) from a spot in the sky near the border of the constellations Ophiuchus and Hercules. The burst flickered with several peaks and lasted somewhere between about 20 and 90 seconds, depending on which instrument and energy range measured it. Swift's X-ray telescope found a fading X-ray afterglow and pinned its position to within about 2 arcseconds, but ultraviolet, optical and infrared searches hours later found no visible afterglow. No distance has been reported, so how far away it is remains unknown. It looks like an ordinary long gamma-ray burst, the kind usually linked to the death of a massive star.
How unusual is it? This is a typical gamma-ray burst: moderate brightness, an X-ray afterglow found, no visible-light afterglow and no distance measured. A redshift (distance) measurement or a supernova or other counterpart found later would make it more notable.
Written by an AI model (claude-sonnet-5-5) from the official reports in this thread; last updated . It may contain mistakes: the reports themselves are the authority.
GRB 261005B: J-band upper limit with WINTER