GCN Circular 45812
GRB 261005B: Swift detection of a burst
From: Jimmy DeLaunay at PSU
Issued: 2026-10-05 22:04 UTC
Why this event is posted: every one of the gamma-ray bursts is posted.
T. M. Parsotan (GSFC), R. Brivio (INAF-OAB), J. J. DeLaunay (PSU),
R. Gupta (NASA GSFC), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa),
A. Mei (INAF-OAB), K. L. Page (U Leicester), D. M. Palmer (LANL) and
C. Salvaggio (INAF-OAB) report on behalf of the Neil Gehrels Swift
Observatory Team:
At 21:39:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 261005B (trigger=1515414). Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec = 255.327, +1.590 deg which is
RA(J2000) = 17h 01m 19s
Dec(J2000) = 01d 35' 25"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a multi-peaked
structure with a duration of about 40 sec. The peak count rate
was ~2000 counts/sec (15-350 keV), at ~4 sec after the trigger.
The XRT began observing the field at 21:41:10.7 UT, 124.1 seconds after
the BAT trigger. No source was detected in the 2.5-s promptly available
image. We are waiting for the full dataset to detect and localise the
XRT counterpart.
There are no UVOT data available at this time.
Burst Advocate for this burst is T. M. Parsotan (tyler.parsotan AT nasa.gov).
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.
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