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Transient Alerts » in reply to GRB 261007A — GRB, X-ray Transient

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In plain words Notable

A burst of gamma rays (the most energetic form of light) was caught on 7 October 2026 by the SVOM satellite, Fermi, and several other space telescopes. It came from a patch of sky toward the constellation Cetus, and the Einstein Probe X-ray telescope also saw it. Within minutes, ground telescopes found a fading optical (visible-light) glow at the spot, and later X-ray and infrared detections confirmed it. A spectrum from the Very Large Telescope in Chile put the burst at redshift 2.101, which means the light left about 10 billion years ago. The burst lasted roughly 23 seconds, which fits the long kind of gamma-ray burst, usually produced when a massive star collapses. The glow faded from about magnitude 15 in the first minutes to about 21.6 a day later. That is a normal fading pattern for an afterglow.

How unusual is it? Most gamma-ray bursts have no measured distance, but this one has a secure spectroscopic redshift of 2.101 and a bright, well-followed afterglow seen in optical, infrared and X-ray light. That makes it notable, but it is otherwise an ordinary long burst, not one of the record-setters.

Written by an AI model (claude-sonnet-5-5) from the official reports in this thread, and rewritten as new reports arrived (version 4); last updated . It may contain mistakes: the reports themselves are the authority.

GRB 261007A: Swift-XRT afterglow detection
GCN Circulars —

GCN Circular 45850
GRB 261007A: Swift-XRT afterglow detection
From: Phil Evans at U of Leicester
Issued: 2026-10-08 07:22 UTC

K.L. Page (U. Leicester), S. Campana (INAF-OAB), A. Melandri
(INAF-OAR), T. Sbarrato (INAF-OAB), S. Dichiara (PSU), D.N. Burrows
(PSU), J.J. DeLaunay (PSU), A.P. Beardmore (U. Leicester) and P.A.
Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
SVOM/ECLAIRs-detected burst GRB 261007A, also known as EP261007a (GCN
Circ. 45828). We searched for X-ray sources in 1.9 ks of Photon
Counting (PC) mode data. The total exposure at the position of the
afterglow (see below) is 1.9 ks, obtained between T0+38.5 ks and
T0+44.0 ks.

An uncatalogued X-ray source is detected and is above the RASS 3-sigma
upper limit at this position, and is therefore likely the GRB
afterglow. The position of this source is also consistent with the
optical counterpart initially discovered by KAIT (GCN Circ. 45825).
Using 1918 s of PC mode data and 2 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 = 11.61403, -17.69197 which is
equivalent to:

RA (J2000): 00h 46m 27.37s
Dec(J2000): -17d 41' 31.1"

with an uncertainty of 2.7 arcsec (radius, 90% confidence). This
position is 2.4 arcmin from the SVOM/ECLAIRs position. The light curve
is currently consistent with a constant source of mean count rate
1.3e-01 ct/sec.

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.74 (+0.29, -0.21). The
best-fitting absorption column is 3.7 (+7.0, -1.6) x 10^20 cm^-2,
consistent with the Galactic value of 2.1 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 3.7 x 10^-11 (4.0 x
10^-11) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Total column: 3.7 (+7.0, -1.6) x 10^20 cm^-2
Galactic foreground: 2.1 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.74 (+0.29, -0.21)

The results of the XRT-team automatic analysis are available at
UKSSDC | Swift-XRT high-level data products for GRB 261007A (swift.ac.uk).
The results of the full analysis of the XRT observations are available
at UKSSDC | Swift ToO GRB Observations | GRB 261007A (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.

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