GCN Circular 45917
GRB 261011A : MITSuME Akeno optical afterglow candidate detection
From: Ichiro Takahashi at Science Tokyo
Issued: 2026-10-12 03:31 UTC
Type: GRB, Afterglow, Optical Transient
I. Takahashi, M. Sasada, H. Hagio, Y. Kubo, A. Ochi, R. Kato, N. Hosoya, J. Yonamine, Y. Yatsu, N. Kawai (Science Tokyo), and M. Niwano (NAOJ) report on behalf of the MITSuME collaboration:
We observed the field of GRB 261011A detected by Swift (Cenko et al., GCN 45896) and SVOM (Huang et al., GCN 45895) with the optical three-color (g', Rc, and Ic) CCD cameras mounted on the MITSuME 50-cm telescope Akeno.
The observations started at 2026-10-11 13:50:44 UT (243 s after the Swift/BAT trigger). We stacked the images obtained under good observing conditions. We detected an optical afterglow candidate at the position reported by Swift-UVOT (Cenko et al., GCN 45896).
The preliminary photometry of the source is as follows:
T0+[sec] | MID-UT | T-EXP[sec] | Magnitudes
----------------------------------------------------------------------------------------------------
580 | 2026-10-11 13:56:21 | 260 | Rc=16.5+/-0.1, Ic=16.2+/-0.1
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T0+ : Elapsed time after the Swift/BAT trigger
T-EXP: Total exposure time
We used the PS1 catalog for flux calibration. The catalog magnitudes in PS1 g, r and i bands were converted to our g', Rc and Ic band magnitudes following Tonry et al. (2012), Table 6. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ; GitHub - MNiwano/Eclaire: Python package using GPU via CUDA for astronomical image reduction (github.com)).
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 : MITSuME Akeno optical afterglow candidate detection
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