GCN Circular 45935
GRB 261010A: Swift-XRT refined Analysis
From: Phil Evans at U of Leicester
Issued: 2026-10-13 07:38 UTC
K.L. Page and P.A. Evans (U. Leicester) reports on behalf of the
Swift-XRT team:
We have analysed 4.7 ks of XRT data for GRB 261010A, from 4.4 ks to
21.5 ks after the trigger. The data are entirely in Photon Counting
(PC) mode.
The light curve can be modelled with a power-law decay with a decay
index of alpha=1.08 (+0.25, -0.24).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.70 (+0.37, -0.22). The
best-fitting absorption column is 4 (+11, -0) x 10^20 cm^-2,
consistent with the Galactic value of 4.6 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 3.9 x 10^-11 (4.2 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 4 (+11, -0) x 10^20 cm^-2
Galactic foreground: 4.6 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.70 (+0.37, -0.22)
If the light curve continues to decay with a power-law decay index of
1.08, the count rate at T+24 hours will be 4.4 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x
10^-13 (1.9 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
UKSSDC | Swift-XRT high-level data products for GRB 261010A (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 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-XRT refined Analysis
The whole thread (25 posts)
- GRB 261010A
- GRB261010A: Retraction of Keck/MOSFIRE near-IR source
- GRB 261010A: Pan-STARRS z-band imaging and upper limit
- GRB 261010A: VLA radio observations
- GRB261010A: Keck/MOSFIRE detection of a near-IR source
- GRB 261010A: ASKAP non-detection of a radio afterglow
- GRB 261010A: LBT tentative near-infrared detection
- GRB 261010A: Glowbug gamma-ray detection
- GRB 261010A: initial pulse rest-frame energetics from Konus-Wind detection
- GRB 261010A: a short minimum variability timescale and a distinct pulse evolution compatible with a merger origin
- GRID detection of GRB 261010A
- GRB 261010A: J-band upper limit by the SYSU 80cm infrared telescope
- GRB 261010A: Swift-XRT refined Analysis
- GRB 261010A: a Type I-L (merger-driven) GRB candidate
- Updated explainer: what the latest reports add (AI-written)
- GRB 261010A: 10.4m GTC spectroscopy of the galaxy 2" from the afterglow
- Konus-Wind detection of GRB 261010A
- GRB 261010A: Swift-BAT refined analysis
- GRB 261010A: NOT confirmation of the optical afterglow
- GRB 261010A: Fermi GBM Observation
- Explainer: what this is and why it matters (AI-written)
- GRB 261010A: Enhanced Swift-XRT position
- GRB 261010A: possible optical afterglow detected with the 1.5m OSN
- GRB 261010A: NOT possible optical counterpart
- GRB 261010A: Swift detection of a burst