GCN Circular 45822
GRB 261005B: Swift-XRT refined Analysis
From: Phil Evans at U of Leicester
Issued: 2026-10-06 22:14 UTC
J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A. D'Ai
(INAF-IASFPA), S. Campana (INAF-OAB), A. Melandri (INAF-OAR), S. Lanava
(PSU), S. Dichiara (PSU), D.N. Burrows (PSU), A.P. Beardmore (U.
Leicester) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 5.1 ks of XRT data for GRB 261005B, from 4.4 ks to
81.3 ks after the trigger. The data are entirely in Photon Counting
(PC) mode. Using 3116 s of PC mode data and 6 UVOT images, we find an
enhanced XRT position (using the XRT-UVOT alignment and matching UVOT
field sources to the USNO-B1 catalogue): RA, Dec = 255.33918, +1.58871
which is equivalent to:
RA (J2000): 17h 01m 21.40s
Dec(J2000): +01d 35' 19.4"
with an uncertainty of 2.1 arcsec (radius, 90% confidence).
The light curve can be modelled with an initial rise, with a power-law
index of alpha=-1.5 (+0.0, -1.0), followed by a break at T+8550 s to
an alpha of 2.7 (+0.6, -0.5).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.15 (+/-0.13). The
best-fitting absorption column is 1.5 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 9.0 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 6.1 x 10^-11 (6.5 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.5 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 9.0 x 10^20 cm^-2
Excess significance: 1.7 sigma
Photon index: 1.15 (+/-0.13)
The results of the XRT-team automatic analysis are available at
UKSSDC | Swift-XRT high-level data products for GRB 261005B (swift.ac.uk).
This circular is an official product of the Swift-XRT team.
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: Swift-XRT refined Analysis