GCN Circular 45965
GRB 261011A: 1.3m DFOT optical upper limit
From: Yash Sharma at Aryabhatta Research Institute of Observational Sciences
Issued: 2026-10-16 16:49 UTC
Type: GRB
Yash Sharma, Amit K. Ror, Shashi B. Pandey (ARIES) report:
We observed the field of GRB 261011A detected by Swift (Cenko et al., GCN 45896) and SVOM (Huang et al., GCN 45895) with the 1.3m Devasthal Fast Optical Telescope (DFOT), located at the Devasthal Observatory of the Aryabhatta Research Institute of Observational Sciences (ARIES), Nainital, India. The observations were started on 2026-10-14 at 18:09:17 UT, i.e., ~ 3.18 days after the Swift/BAT trigger (T0 = 2026-10-11 13:46:41 UT). We obtained multiple frames with an exposure time of 300 s each in the R filter. The images were aligned and stacked.
We do not detect any optical afterglow emission down to the 3-sigma background limit at the optical afterglow position reported by Swift/UVOT (Cenko et al., GCN 45896) and refined by SOAR (Cheng et al., GCN 45922), nor within the 2.9 arcsec error radius of the enhanced Swift-XRT position (Page et al., GCN 45933; Melandri et al., GCN 45934).
We obtain the following 3-sigma upper limit from the stacked image:
Date Start_UT T_start-T0 (days) Filter Exp time (s) Magnitude (3-sigma)
===================================================================================
2026-10-14 18:09:17 ~ 3.18 R 12 x 300 s > 22.0
The non-detection of the optical counterpart is consistent with the rapid fading of the afterglow at z = 2.407 (Pérez-García et al., GCN 45931; Monsalves et al., GCN 45920) and later-epoch optical/NIR upper limits reported by REM (Brivio et al., GCN 45926), SYSU (Wen et al., GCN 45942), and SAO RAS (Moskvitin et al., GCN 45951).
Photometric calibration was performed against secondary standard stars from the Pan-STARRS (PS1) catalog with Zero Point = 4.081 ± 0.015 mag. The reported limiting magnitude is in the AB system and has not been corrected for the Galactic extinction. This circular may be cited.
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: 1.3m DFOT optical upper limit
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