STARITHM
GRB 260921A detected with high significance across multiple instruments
AI Summary
The Fermi GBM and Swift BAT detected a long-duration gamma-ray burst (GRB 260921A) on September 21, 2026, with significant emission lasting approximately 10 seconds. Follow-up observations from NuSTAR, SVOM/GRM, and AstroSat/CZTI confirmed the burst's multipeaked structure and provided detailed spectral analysis.
Measurements
| Event | GRB 260921A |
|---|---|
| Event ID | 811675753 |
| Source | Fermi GBM |
| Alert type | GRB |
| Significance | high |
| Trigger time (UTC) | Mon, 21 Sep 2026 09:29:08 GMT |
| Right ascension (J2000) | 145.376° |
| Declination (J2000) | 2.849° |
| Position error radius | 0.016666666666666666° (60.0″) |
| Position from | Swift-BAT position, GCN 45686 |
| GCN notices | 5 |
| GCN circulars | 11 |
Every localisation reported in Circulars (2)
| Instrument | Of | Error | Circular |
|---|---|---|---|
| Fermi-GBM | burst | 1.40° (1-sigma statistical) | GCN 45674 |
| Swift-BAT | burst | 60.0″ (90%) | GCN 45686 |
Burst properties (11)
As each instrument's Circular reported them; values parsed from the Circular text.
| Property | Value | Band | Instrument | Spectral model | Circular |
|---|---|---|---|---|---|
| Duration | 8.9 s | — | Konus-Wind | — | GCN 45722 |
| Fluence | 7.93 1e-6 erg/cm2 | 20 keV - 10 MeV | Konus-Wind | — | GCN 45722 |
| Peak flux | 3.71 1e-6 erg/cm2/s | 20 keV - 10 MeV | Konus-Wind | — | GCN 45722 |
| Photon index | -0.92 | 20 keV - 10 MeV | Konus-Wind | — | GCN 45722 |
| Photon index | -2.3 | 20 keV - 10 MeV | Konus-Wind | — | GCN 45722 |
| Photon index | -0.9 | 20 keV - 10 MeV | Konus-Wind | — | GCN 45722 |
| Photon index | -2.3 | 20 keV - 10 MeV | Konus-Wind | — | GCN 45722 |
| Epeak | 334 keV | 20 keV - 10 MeV | — | — | GCN 45722 |
| Epeak | 308 keV | 20 keV - 10 MeV | — | — | GCN 45722 |
| Epeak | 768 keV | 1 keV - 10 MeV | — | — | GCN 45722 |
| Epeak | 708 keV | 1 keV - 10 MeV | — | — | GCN 45722 |
Observations (15)
Values parsed from the Circular text; each row names its Circular.
| Time since trigger | Band | Value | Telescope | Circular |
|---|---|---|---|---|
| T+80 s | C | > 15.5 mag (limit) | MASTER-OAFA | GCN 45677 |
| T+91 s | C | > 15.2 mag (limit) | MASTER-OAFA | GCN 45677 |
| T+117 s | C | > 15.3 mag (limit) | MASTER-OAFA | GCN 45677 |
| T+2 min | C | > 15.3 mag (limit) | MASTER-OAFA | GCN 45677 |
| T+3 min | C | > 15.2 mag (limit) | MASTER-OAFA | GCN 45677 |
| T+4 min | C | > 15.5 mag (limit) | MASTER-OAFA | GCN 45677 |
| T+5 min | C | > 15.1 mag (limit) | MASTER-OAFA | GCN 45677 |
| T+6 min | C | > 15.3 mag (limit) | MASTER-OAFA | GCN 45677 |
| T+7 min | C | > 14.9 mag (limit) | MASTER-OAFA | GCN 45677 |
| T+8 min | C | > 14.6 mag (limit) | MASTER-OAFA | GCN 45677 |
| T+10 min | C | > 15.3 mag (limit) | MASTER-OAFA | GCN 45677 |
| — | 0.3-10 keV | 1500 cps | NuSTAR | GCN 45727 |
| — | 20-200 keV | 123 ± 27 counts/s | AstroSat | GCN 45687 |
| — | 100-500 keV | 563 ± 58 counts/s | AstroSat | GCN 45687 |
| — | white | 14 mag | MASTER-OAFA | GCN 45678 |
Swift data
GRB 260921A, Swift/BAT trigger 1512356: Swift GRB table · XRT position · XRT light curve · Burst analyser
Notices (1)
Fermi GBM — GRB · Mon, 21 Sep 2026 09:29:08 GMT
GCN Circulars (11)
GCN-45727 — GRB 260921A
· Thu, 24 Sep 2026 15:38:08 GMT
The NuSTAR SINGS working group detected prompt emission from GRB 260921A, a gamma-ray burst also observed by multiple other satellites including Fermi-GBM and Swift-BAT. The event lasted approximately 10 seconds with a peak count rate of 1500 counts per second.
GCN-45726 — GRB 260921A
· Thu, 24 Sep 2026 15:34:09 GMT
The Konus-Wind Team has corrected an error in the rest-frame peak energy values of GRB 260921A, which were previously over-corrected for redshift. With the correct values, GRB 260921A is now consistent with the Amati and Yonetoku relations for long gamma-ray bursts.
GCN-45725 — GRB 260921A
· Thu, 24 Sep 2026 14:26:37 GMT
The SVOM/GRM instrument detected a gamma-ray burst, GRB 260921A, on September 21, 2026, which was also observed by multiple other telescopes. The burst exhibited multiple pulses with a duration (T90) of 8.0 seconds and a power law spectrum with an exponential cutoff.
GCN-45722 — GRB 260921A
· Thu, 24 Sep 2026 13:39:33 GMT
The Konus-Wind instrument detected a long-duration gamma-ray burst (GRB 260921A) on September 21, 2024, at 09:29:07.045 UT. The burst, which lasted approximately 8.9 seconds, is notable for its multipeaked structure and high energy emission, and is potentially of merger origin.
GCN-45687 — GRB 260921A
· Tue, 22 Sep 2026 05:23:16 GMT
A gamma-ray burst, GRB 260921A, was detected by AstroSat's CZTI instrument on September 21, 2026, at 09:29:13.18 UTC. The burst was also observed by Fermi and Swift BAT, with significant emission peaks detected in both the CZT and CsI anticoincidence (Veto) detectors, indicating a strong and multi-peaked event.
GCN-45686 — GRB 260921A
· Tue, 22 Sep 2026 01:58:07 GMT
The Swift-BAT team has refined the analysis of GRB 260921A, determining its position with an uncertainty of 1.0 arcmin and characterizing its light curve and spectrum. The burst exhibited a single-pulse structure with a duration of approximately 8.62 seconds and a power-law spectrum with an index of 1.29.
GCN-45684 — GRB 260921A
· Mon, 21 Sep 2026 18:45:14 GMT
On 21 September 2026, the Fermi Gamma-ray Burst Monitor detected GRB 260921A, which was also observed by Swift BAT and had a possible optical counterpart with a candidate host galaxy at a redshift of 1.3. The event had a duration of approximately 17.3 seconds and a peak photon flux of 12.3 ph/s/cm^2 in the 10-1000 keV band.
GCN-45678 — GRB 260921A
· Mon, 21 Sep 2026 10:29:29 GMT
The MASTER-OAFA robotic telescope detected a possible optical counterpart, MASTER OT J094129.58+025052.5, to the gamma-ray burst Swift GRB 260921A, with a magnitude of approximately 14. This detection is associated with a host galaxy at a redshift of z=1.3.
GCN-45677 — GRB 260921A
· Mon, 21 Sep 2026 09:59:36 GMT
The MASTER-OAFA robotic telescope in Argentina observed the Swift GRB 260921A error box starting 80 seconds after the trigger, with upper limits up to 15.5 magnitude. Observations were conducted under twilight conditions, and the data is being continuously updated and analyzed.
GCN-45676 — GRB 260921A
· Mon, 21 Sep 2026 09:52:28 GMT
The Swift Burst Alert Telescope (BAT) detected a gamma-ray burst, GRB 260921A, on September 26, 2021, at 09:29:12 UT. The burst had a complex structure with a duration of about 10 seconds and a peak count rate of approximately 4500 counts/sec. Swift's automatic slews are currently disabled, and the burst is Sun-constrained until October 8, 2021, preventing further XRT or UVOT data collection.
GCN-45674 — GRB 260921A
· Mon, 21 Sep 2026 09:39:40 GMT
The Fermi Gamma-ray Burst Monitor (GBM) detected a likely long gamma-ray burst (GRB 260921A) on September 21, 2026, at 09:29:08 UT. The event was located at RA = 148.9, Dec = 0.6 (J2000) with a statistical uncertainty of 1.4 degrees.
AI summary generated Thu, 05 Nov 2026 13:22:08 GMT.