GCN Circular 45930
GRB 261011A: Swift-BAT refined analysis
From: Amy
Issued: 2026-10-13 00:39 UTC
S. D. Barthelmy (GSFC), R. Gupta (GSFC), H. A. Krimm (NSF), S. Laha
(GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), M. J. Moss
(GSFC), D. M. Palmer (LANL), T. Parsotan (GSFC), D. Sadaula (GSFC/UMBC), T.
Sakamoto (AGU) (i.e. the Swift-BAT team):
Using the data set from T-179 to T+723 sec from the recent telemetry
downlink, we report further analysis of BAT GRB 261011A (trigger #1516664)
(Cenko et al., GCN Circ. 45896). The BAT ground-calculated position is
RA, Dec = 21.911, -21.550 deg which is
RA(J2000) = 01h 27m 38.7s
Dec(J2000) = -21d 33' 00.7"
with an uncertainty of 1.0 arcmin, (radius, sys+stat, 90% containment). The
partial coding was 29%.
The mask-weighted light curve shows a multi-peaked structure that starts
~T+100 s and ends at ~T+210 s. T90 (15-350 keV) is 78.90 +- 18.49 sec
(estimated error including systematics). Note that the particularly unusual
light curve mentioned in the original circular (Cenko et al., GCN Circ.
45896) is no longer visible in the ground analysis. Further investigation
shows that there were some noisy detectors producing coincidental
pulse-like structures around the GRB time, and thus those pulses seen in
the raw light curve prior to ~T+100 s are not astrophysical.
The time-averaged spectrum from T+103.61 to T+208.74 sec is best fit by a
simple power-law model. The power law index of the time-averaged spectrum
is 1.50 +- 0.07. The fluence in the 15-150 keV band is 6.3 +- 0.3 x 10^-06
erg/cm2. The 1-sec peak photon flux measured from T+171.74 sec in the
15-150 keV band is 3.0 +- 0.4 ph/cm2/sec. All the quoted errors are at the
90% confidence level.
The results of the batgrbproduct analysis are available at
batgrbproduct analysis for trigger=1516664 (swift.gsfc.nasa.gov)
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: Swift-BAT refined analysis
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