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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: VLA radio observations
GCN Circulars —

GCN Circular 45961
GRB 261010A: VLA radio observations
From: Genevieve Schroeder at Cornell University
Issued: 2026-10-16 14:30 UTC
Type: GRB, Radio Transient

G. Schroeder (U. Toronto), W. Fong (Northwestern), J. Rastinejad (UMD), Gokul Srinivasaragavan (Northwestern) report:

We observed the location of GRB 261010A (Fermi GBM team, GCN 45888; Lien et al., GCN 45889; Frederiks et al., GCN 45925, Cheung et al., GCN 45950) with the Karl G. Jansky Very Large Array (VLA) in D configuration under program 26A-062 (PI Schroeder) for 0.75 hour at a mean frequency of 10 GHz and mid time of 2026 Oct 15 at 23:40 UT (5.1 days post-burst).

In preliminary analysis, we do not detect any radio sources at or near the position of the afterglow (Osborne et al., GCN 45894, O’Neill et al., GCN 45890; Aceituno et al., GCN 45891; Corcoran et al., GCN 45912), to a 3-sigma limit of < 20 microJy.

At z=0.070 (Corcoran et al., GCN 45912) this limit corresponds to a rest-frame luminosity of < 2e27 erg/s/Hz. This luminosity limit is 1-2 orders of magnitude lower than the typical range for radio detected short GRBs (e.g., Anderson et al. 2025) and an order of magnitude deeper than the strongest radio limits on short GRBs. This limit is also ~4 times lower than the long merger-driven GRB 230307A (e.g. Levan et al. 2024), but similar to limits placed on the long merger-driven GRB 211211A (e.g. Rastinejad et al. 2022). At z=0.785 (Castro-Tirado et al., GCN 45928), this corresponds to a rest-frame luminosity of < 3e29 erg/s/Hz. This luminosity limit is comparable to limits placed on short GRBs with no radio detections, but is about an order of magnitude lower than the typical range for long GRBs from collapsars (e.g. Chandra and Frail 2012).

Further observations are planned. We thank the VLA staff for quickly approving and executing these observations.

Every one of the gamma-ray bursts GCN reports is posted here.
Relayed automatically from NASA's General Coordinates Network.

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