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

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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 / EP261007a: VLT/X-shooter spectroscopic redshift z = 2.101
GCN Circulars —

GCN Circular 45829
GRB 261007A / EP261007a: VLT/X-shooter spectroscopic redshift z = 2.101
From: Andrea Saccardi at CEA/Irfu
Issued: 2026-10-07 09:42 UTC
Type: GRB, X-ray Transient

A. Saccardi (CEA/Irfu), B. Schneider (LAM), N. Habeeb (U. Leicester), D. B. Malesani (DAWN/NBI and Radboud), S. D. Vergani (LUX-Paris Obs.), M. Garnichey (LUX-Paris Obs.), J. An (NAOC), report on behalf of the Stargate collaboration:

We observed the optical counterpart (Zheng et al., GCN 45825) of the SVOM/ECLAIRs GRB 261007A (Goto et al., GCN 45824), also detected by EP/WXT (Wen et al., GCN 45828), using the ESO VLT UT3 (Melipal) equipped with the X-shooter spectrograph.

In a 3x15 s r-band exposure taken with the acquisition camera (1.21 hr after the SVOM trigger), the counterpart is detected with a magnitude r = 18.53 +/- 0.04 (AB), calibrated against Pan-STARRS and not corrected for Galactic extinction.

A spectrum covering the wavelength range 3000-21000 AA was secured, with a total exposure time of 2x600 s in each of the UVB, VIS, and NIR arms. Our observations started at 07:03:33 on 2026 October 7 (1.36 hr after the SVOM trigger).

In a preliminary reduction of the spectra, we clearly detect a continuum in each arm, and a broad trough at ~3770 AA, consistent with Lyman alpha. From the detection of multiple narrow absorption features, including N V, S II, Si II, Si II*, O I, O I*, Ni II, C II, C II*, C IV, Si IV, Fe II, Al II, Al III, Cr II, Zn II, Fe II*, Ni II*, Mn II, Mg II, Mg I, and Ca II, we infer a redshift of z = 2.101. The detection of fine-structure lines also confirms the physical association between this absorption system and the high-energy transient. We thus securely conclude that GRB 261007A / EP261007a is at z = 2.101.

We also detect several intervening systems, in particular a sub-DLA at z = 1.79 (Lya, Mg II, Si II, Fe II) and a system at z = 1.83 showing many absorption lines (C IV, Si IV, Fe II, Al II, Al III, Mg II, Mg I).

We acknowledge excellent support from the ESO staff in Paranal.

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

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