GCN Circular 45931
GRB 261011A: 10.4m GTC spectroscopic redshift (z = 2.407)
From: I. Perez-Garcia at Instituto de Astrofísica de Andalucía
Issued: 2026-10-13 05:21 UTC
Type: GRB
I. Pérez-García (IAA-CSIC), Y.-D. Hu (GXU), A. J. Castro-Tirado (IAA-CSIC), F. J. Aceituno, M.D. Caballero-Garcia, E. Fernandez-Garcia, M. Gritsevich, S. Guziy (IAA-CSIC), D. Garcia-Alvarez, A. Tejero (GRANTECAN, IAC), on behalf of a larger collaboration, report:
We observed the optical afterglow of GRB 261011A detected by SVOM/ECLAIRs (Huang et al. GCN 45895), Swift/BAT (Cenko et al. GCN 45896) and Konus-Wind (Ridnaia et al. GCN 45924), with the 10.4m Gran Telescopio Canarias (equipped with the OSIRIS+ spectrograph) in La Palma (Spain). Long-slit spectra were taken starting on Oct 12, 2026, 00:19 UT (i.e. 10.5 h post burst) with both the R1000R grism (1200 s) and the R1000B grism (600 s), with the slit centred on the optical afterglow position (Cenko et al., GCN 45896; O'Neill et al., GCN 45897; Fu et al., GCN 45898; Izzo et al., GCN 45899; Wu et al., GCN 45900; Yin et al., GCN 45901; Shi et al., GCN 45903; Aryan et al., GCN 45904; Arya et al., GCN 45907; Izzo et al., GCN 45909; Huang et al., GCN 45913; Bochenek et al., GCN 45914; Li et al., GCN 45915; Zhao et al., GCN 45916; Takahashi et al., GCN 45917; Cheng et al., GCN 45922).
A faint continuum of the afterglow is detected across the full range. On top of it, we identify low S/N ratio absorption features consistent with Fe II (2344, 2374, 2382 A), Al II (1670 A) and Al III (1854/1862 A), all at a common redshift z = 2.407 +/- 0.001.
A joint analysis of all the expected lines gives the above mentioned, unique solution, at this redshift over the range 1.5 < z < 4.2. Moreover, we notice that the flux drops strongly below ~4270 A, consistent with the damped Lyman-alpha absorption trough at this redshift.
This confirms the tentative redshift z = 2.405 derived by Monsalves et al. (GCN 45920) from the damped Lyman-alpha trough in the VLT/X-shooter spectrum.
In addition to this, we notice that the Legacy Survey DR10 shows a faint source (r = 25.4 AB), coincident with the afterglow position within 0.1 arcsec, a likely host galaxy candidate.
We thank the staff at GTC for their excellent support.
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 261011A — GRB, X-ray Transient
In plain words Notable
On 11 October 2026 two satellites, SVOM and Swift, caught a long gamma-ray burst (a brief flash of high-energy light from a distant exploding star) in the southern sky. It lasted roughly a minute or more, depending on the instrument. Within minutes, telescopes around the world saw a fading visible-light and X-ray afterglow at the same spot. Two large telescopes measured the distance from the light's fingerprints: the burst happened at redshift 2.407, meaning the light left roughly 11 billion years ago. The afterglow faded below detection within about a day, and no host galaxy has been clearly detected. It is most likely an ordinary long burst from the collapse of a massive star. Swift's first report of an unusual light curve was withdrawn after a closer look showed that part of it came from noisy detectors.
How unusual is it? Most gamma-ray bursts have no measured distance, but this one has a confirmed redshift (2.407) from two independent telescopes plus a bright afterglow seen in many wavelengths; otherwise its properties look typical, and the initially reported oddity turned out to be instrumental noise.
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 261011A: 10.4m GTC spectroscopic redshift (z = 2.407)
The whole thread (32 posts)
- GRB 261011A — GRB, X-ray Transient
- GRB 261011A: 1.3m DFOT optical upper limit
- GRB 261011A: SAO RAS and AbAO optical observations
- GRB 261011A: Later-epoch J-band upper limit from the SYSU 80 cm infrared telescope
- GRB 261011A: GECAM-B observation
- GRB 261011A: Swift-XRT refined Analysis
- GRB 261011A: Enhanced Swift-XRT position
- GRB 261011A: 10.4m GTC spectroscopic redshift (z = 2.407)
- GRB 261011A: Swift-BAT refined analysis
- GRB 261011A: REM optical/NIR observations
- Konus-Wind detection of GRB 261011A
- Updated explainer: what the latest reports add (AI-written)
- GRB 261011A: SOAR optical afterglow observations at ~17 hours
- GRB 261011A: VLT/X-shooter redshift constraints
- GRB 261011A : MITSuME Akeno optical afterglow candidate detection
- GRB 261011A: Optical followup from Sichuan South Observatory
- GRB 261011A: GMG Optical Observation
- GRB 261011A: Liverpool Telescope optical observations
- GRB 261011A: J-band observations by the SYSU 80cm infrared telescope
- GRB 261011A: continued LCO optical observations
- GRB 261011A: GROWTH-India Telescope optical observations
- GRB 261011A: Optical upper limits with a 28cm telescope in Chengde
- Swift GRB 261011A: Global MASTER-Net observations report
- GRB 261011A: Optical follow-up observations with Kinder
- GRB 261011A: SVOM/C-GFT optical observations
- GRB 261011A: LCO optical observations
- GRB 261011A: SVOM/VT optical observation from VHF data
- GRB 261011A: LCO optical observations
- GRB 261011A: TRT optical afterglow detection
- Explainer: what this is and why it matters (AI-written)
- GRB 261011A: GOTO optical counterpart detection
- GRB 261011A: Swift detection of an unusual burst