GCN Circular 45922
GRB 261011A: SOAR optical afterglow observations at ~17 hours
From: Cheng Cheng at CAS South America Center for Astronomy (CASSACA)
Issued: 2026-10-12 12:56 UTC
Type: GRB, Afterglow, Optical Transient
Cheng Cheng (CASSACA, NAOC), Liping Xin (NAOC), Jia-Sheng Huang (CASSACA, NAOC) report:
We observed the field of GRB 261011A (SVOM/ECLAIRs: Huang et al., GCN 45895; Swift/BAT: Cenko et al., GCN 45896) with the 4.1-m SOAR telescope (GHTS red imager) beginning on 2026-10-12 at 06:45:36 UT, i.e. 17.06 h after the Swift/BAT trigger.
We obtained 3 x 180 s exposures in each of the SDSS g, r and z filters. The frames were trimmed, astrometrically solved, sky-subtracted and median-combined onto a common output grid (0.2894"/pixel), so that the three band images are pixel-aligned. Each stacked image is 1000 x 1000 pixels (4.8' x 4.8'), centred on the target coordinates.
We detect the afterglow at
RA, Dec (J2000) = 01:27:35.40, -21:33:37.7
with an uncertainty of 0.15" (the astrometry is tied to Gaia DR3; a cross-check against LS DR11/DECaLS gives a residual scatter of 0.10"). This position lies 0.52" from the Swift/UVOT position reported by Cenko et al. (GCN 45896), fully consistent with its 1.1" error radius, and refines it.
Photometry was carried out with SExtractor in dual mode, using the r-band image as the detection image and measuring MAG_AUTO magnitudes on the g, r and z images with a local background estimate. Magnitudes were calibrated against LS DR11 (DECaLS) stars and are in the AB system:
g = 23.93 +/- 0.14 (phot) +/- 0.08 (zeropoint)
r = 22.75 +/- 0.08 (phot) +/- 0.09 (zeropoint)
z = 22.43 +/- 0.18 (phot) +/- 0.15 (zeropoint)
The first uncertainty is the photometric error and the second is the zeropoint (calibration) uncertainty, which is systematic across the field and therefore should not be treated as an independent error when combining this measurement with others.
The source is unresolved (FWHM = 1.2"), and no host galaxy is detected at this depth; the LS DR11 source at this position (ls_id_dr11 = 48423370429045300) has r = 25.63 +/- 0.30 AB mag.
We thank the SOAR staff for the rapid execution of these observations.
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: SOAR optical afterglow observations at ~17 hours
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