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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: Swift detection of a burst
GCN Circulars —

GCN Circular 45889
GRB 261010A: Swift detection of a burst
From: Jimmy DeLaunay at PSU
Issued: 2026-10-10 19:34 UTC

A. Y. Lien (U Tampa), R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL),
M. J. Moss (GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and
M. H. Siegel (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 19:17:07 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 261010A (trigger=1516528). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec = 248.752, 26.609 deg, which is
RA(J2000) = 16h 35m 00s
Dec(J2000) = 26d 36' 33"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a single-peaked
structure with a duration of at least 5 sec. The peak count rate
was ~7000 counts/sec (15-350 keV), at ~0 sec after the trigger.
There may be additional pulse structures that are caused either
by the burst or by entry into the SAA. Additional ground data are
required to distinguish the burst emission from background noise.

The XRT began observing the field at 19:18:41.4 UT, 94.2 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 248.7491, 26.5802 which is equivalent to:
RA(J2000) = 16h 34m 59.78s
Dec(J2000) = +26d 34' 48.7"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This
location is 104 arcseconds from the BAT onboard position, within the
BAT error circle. No event data are yet available to determine the
column density using X-ray spectroscopy.

UVOT data are unavailable at this time

Burst Advocate for this burst is A. Y. Lien (yarleen AT gmail.com).
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: Welcome to the Neil Gehrels Swift Observatory (swift.psu.edu))

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

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