Long GRB 261029A detected by Fermi/GBM and SVOM at z=3.27 with bright optical counterpart

AI Summary

A long-duration gamma-ray burst (GRB 261029A) was detected on 2026-10-29 at 01:27:03 UTC by Fermi/GBM (trigger 814930028) and SVOM/ECLAIRs, with T90 duration of 40-47.5 seconds and peak energy ~900 keV. The burst was localized to RA=8.817988, Dec=34.500138 with refined position from multiple instruments (NuSTAR, GECAM-B, CALET). An optical counterpart was rapidly identified by GOTO and confirmed at redshift z=3.27 via NOT spectroscopy, with initial brightness L~14 mag fading to r~20+ mag over hours. Multi-wavelength follow-up including Fermi-LAT (2.5 GeV photon detected), X-ray observations (EP-FXT, NuSTAR), and extensive optical/IR monitoring from ground-based telescopes confirmed this as a Type II GRB with isotropic energy ~3.6×10⁵⁴ erg, consistent with the Amati relation.

Measurements

Notices (2)

Fermi GBM — GRB · Thu, 29 Oct 2026 01:27:03 GMT

Fermi — XRAY · Thu, 29 Oct 2026 01:27:03 GMT

GCN Circulars (29)

GCN-46117 — GRB 261029A · Fri, 30 Oct 2026 21:20:44 GMT
The SVOM/ECLAIRs team has refined the analysis of GRB 261029A, a gamma-ray burst detected by multiple observatories, including Fermi, AstroSat, and NuSTAR. The burst exhibited a multiple peak light curve with a duration of 47.5 seconds and a refined localization that is close to the afterglow position determined by GOTO.

GCN-46113 — GRB 261029A · Fri, 30 Oct 2026 15:02:52 GMT
The PKU 60cm Telescope at Xinglong Observatory observed the field of GRB 261029A approximately 1.4 days after its detection by Fermi/GBM and SVOM/ECLAIRs, but no significant optical counterpart was found. The 3-sigma upper limits derived were r > 22.14 mag and i > 21.48 mag, indicating the absence of a detectable optical signal at the reported position.

GCN-46112 — GRB 261029A · Fri, 30 Oct 2026 14:45:24 GMT
The Glowbug gamma-ray telescope on the International Space Station detected a bright, multi-peaked gamma-ray burst (GRB 261029A) from approximately 2 to 10 seconds after the trigger time, which was also detected by multiple other observatories. The detection occurred during a period of high background radiation in the northern radiation belt, and the analysis is preliminary.

GCN-46109 — GRB 261029A · Fri, 30 Oct 2026 09:02:16 GMT
The SVOM/GWAC-F60 telescope at Xinglong Observatory, China, observed the field of GRB 261029A and detected its optical counterpart with a magnitude of 19.67 in the R-band, approximately 9.32 hours after the initial trigger. This observation is part of a broader follow-up effort involving multiple astronomers and institutions.

GCN-46108 — GRB 261029A · Fri, 30 Oct 2026 08:00:02 GMT
The GECAM-B satellite detected a bright gamma-ray burst, GRB 261029A, on October 29, 2026, which was also observed by multiple other instruments. The burst, with a duration of 40 seconds and a high-energy cutoff at 914 keV, is consistent with Type II GRBs and has an isotropic energy of about 3.6E54 erg.

GCN-46104 — GRB 261029A · Fri, 30 Oct 2026 02:41:48 GMT
The Wide Field Survey Telescope (WFST) detected the optical counterpart of GRB 261029A approximately 10.98 hours after its initial detection by Fermi GBM and SVOM/ECLAIRs, with a measured g-band magnitude of 20.73. This observation confirms the presence of the optical transient associated with the gamma-ray burst.

GCN-46103 — GRB 261029A · Fri, 30 Oct 2026 00:09:44 GMT
The long gamma-ray burst GRB 261029A was detected by multiple observatories at a redshift of z = 3.27. Observations with the LCO 1-m telescope at Siding Spring Observatory detected the optical counterpart in r', i', and g' filters, with AB magnitudes of 19.61±0.05, 19.33±0.07, and 20.78±0.10 respectively.

GCN-46102 — GRB 261029A · Thu, 29 Oct 2026 23:20:31 GMT
The Ondrejov D50 robotic telescope observed a possible rebrightening of the afterglow from GRB 261029A, reaching a magnitude of i~19.6 at 0.75 days post-burst before starting to decay again. This event was detected using a series of 60-second Sloan i'-band exposures starting at 16:42UT on 2026 October 29.

GCN-46101 — GRB 261029A · Thu, 29 Oct 2026 22:44:59 GMT
The Liverpool Telescope detected the afterglow of GRB 261029A with a magnitude of 20.37 in the r-band, consistent with a temporal decay index of approximately 1.4. This observation was part of a collaborative effort involving multiple institutions and telescopes.

GCN-46100 — GRB 261029A · Thu, 29 Oct 2026 18:20:35 GMT
NuSTAR detected bright prompt emission from the long-duration GRB 261029A, which was also observed by multiple other observatories including Fermi-GBM and SVOM. The event showed a double-peaked burst lasting about 40 seconds with a peak count rate of approximately 4000 counts per second.

GCN-46099 — GRB 261029A · Thu, 29 Oct 2026 17:36:17 GMT
The 60cm Panzhihua Telescope detected the optical counterpart of GRB 261029A, initially identified by Fermi/GBM and SVOM/ECLAIRs, approximately 12.19 hours after the trigger, with a magnitude of 20.23 in the L band. This detection is part of a collaborative effort involving multiple institutions and telescopes.

GCN-46098 — GRB 261029A · Thu, 29 Oct 2026 17:16:12 GMT
On October 29, 2026, the Fermi Gamma-ray Burst Monitor detected GRB 261029A, which was also observed by multiple other telescopes and instruments. The event had a redshift of z = 3.27 and exhibited a complex light curve with a duration of about 43.8 seconds.

GCN-46097 — GRB 261029A · Thu, 29 Oct 2026 17:15:07 GMT
The robotic telescopes FRAM-ORM and FRAM-Auger detected the optical afterglow of GRB 261029A, with observations starting approximately 11.5 minutes post-trigger and continuing for over two hours. The afterglow showed a steeper decay initially, followed by a shallower power-law decline, providing valuable data for understanding the behavior of gamma-ray bursts.

GCN-46096 — GRB 261029A · Thu, 29 Oct 2026 16:20:14 GMT
The SVOM/GRM instrument detected a bright gamma-ray burst, GRB 261029A, on October 29, 2026, which was also observed by Fermi/GBM and SVOM/ECLAIRs. The burst, located at RA = 8.817988, Dec = 34.500138, had a T90 duration of 43.50 seconds and a measured redshift of z=3.275, indicating it is a Type II GRB consistent with the 'Amati' relation.

GCN-46095 — GRB 261029A · Thu, 29 Oct 2026 16:07:41 GMT
The CALET Gamma-Ray Burst Monitor detected GRB 261029A on October 29, 2026, at 01:27:33.19 UTC, with the burst signal showing a multi-peaked structure and lasting approximately 32.2 seconds. This event was also independently reported by multiple other observatories including Fermi GBM, SVOM, Fermi-LAT, and AstroSat CZTI.

GCN-46092 — GRB 261029A · Thu, 29 Oct 2026 14:15:17 GMT
The SVOM/VT telescope detected the optical counterpart of the gamma-ray burst GRB 261029A in both VT_B and VT_R bands, approximately 46 minutes after the initial trigger. The burst was also observed by multiple other telescopes including Fermi/GBM, Fermi/LAT, and AstroSat CZTI, highlighting its significance in multi-wavelength astronomy.

GCN-46090 — GRB 261029A · Thu, 29 Oct 2026 13:32:54 GMT
The PKU 60cm Telescope at Xinglong Observatory detected the optical counterpart of GRB 261029A in both r- and i-bands approximately 10 hours after the initial trigger by Fermi/GBM and SVOM/ECLAIRs. The observations confirmed the position of the optical transient, consistent with previous reports, with a magnitude of 19.74 in the r-band.

GCN-46089 — GRB 261029A · Thu, 29 Oct 2026 13:26:02 GMT
The AstroSat CZTI collaboration detected a gamma-ray burst, GRB 261029A, which was also observed by Fermi, SVOM, and Fermi LAT. The burst showed multiple peaks of emission, with significant peak count rates and a total duration (T90) of approximately 38 seconds.

GCN-46088 — GRB 261029A · Thu, 29 Oct 2026 12:59:21 GMT
The SVOM/C-GFT telescope detected the optical counterpart of GRB 261029A in g, r, and i bands approximately 8.79 hours after the initial trigger, with magnitudes of 20.86, 19.44, and 19.41 respectively. This observation is part of a coordinated effort to study the afterglow of the gamma-ray burst.

GCN-46086 — GRB 261029A · Thu, 29 Oct 2026 09:33:51 GMT
The Einstein Probe (EP) performed a follow-up observation of the gamma-ray burst GRB 261029A, detecting an uncataloged X-ray source that closely matches the position of an optical counterpart candidate. This observation, conducted about 47 minutes after the initial detection by SVOM/ECLAIRs, provides significant data for further analysis of the event.

GCN-46085 — GRB 261029A · Thu, 29 Oct 2026 08:20:47 GMT
On October 29, 2026, the Fermi-LAT detected high-energy emission from GRB 261029A, which was also observed by Fermi-GBM, SVOM, and GOTO. The optical counterpart was identified at a redshift of z = 3.27, with significant high-energy photon flux and a highest energy photon of 2.5 GeV.

GCN-46084 — GRB 261029A · Thu, 29 Oct 2026 07:10:42 GMT
The SVOM/ECLAIRs GRB 261029A was observed using the LCO 1m telescope at Cerro Tololo Observatory, detecting an optical counterpart with magnitudes r = 17.25 and z = 17.64. This observation provides crucial follow-up data on the gamma-ray burst event.

GCN-46083 — GRB 261029A · Thu, 29 Oct 2026 06:40:42 GMT
The SVOM/COLIBRÍ telescope detected the optical afterglow of GRB 261029A, with a preliminary magnitude of 14.41 in the r filter, showing fading over time. This detection confirms the source reported by multiple other observations and provides crucial data for further analysis.

GCN-46081 — GRB 261029A · Thu, 29 Oct 2026 05:41:22 GMT
The optical and near-infrared counterpart of GRB 261029A was observed using the Nordic Telescope, revealing a redshift of z = 3.27. This redshift was determined through spectroscopic observations that identified multiple absorption features at a common redshift, indicating the distance and age of the gamma-ray burst.

GCN-46079 — GRB 261029A · Thu, 29 Oct 2026 05:03:21 GMT
The KAIT telescope at Lick Observatory detected the optical counterpart of GRB 261029A, measuring a magnitude of 17.15 in the R filter about 2.2 hours after the initial trigger. The source was observed to be fading in subsequent observations, confirming the detection.

GCN-46078 — GRB 261029A · Thu, 29 Oct 2026 04:24:56 GMT
The Thai Robotic Telescope network (TRT) observed the optical counterpart of GRB 261029A, detected by Fermi and potentially SVOM, with a brightness of R = 17.41 at 2.30 hours post-trigger. The observations are ongoing.

GCN-46073 — GRB 261029A · Thu, 29 Oct 2026 02:20:34 GMT
The Gravitational-wave Optical Transient Observer (GOTO) detected a new optical source, GOTO26llt/AT2026ahaw, within the localization region of the gamma-ray burst GRB 261029A. This source, initially bright at L = 13.98 AB mag, faded to L = 14.85 AB mag within a short period, indicating a potential optical counterpart to the gamma-ray burst.

GCN-46072 — GRB 261029A · Thu, 29 Oct 2026 02:02:11 GMT
The SVOM mission detected a gamma-ray burst, GRB 261029A, on October 29, 2026, at 01:27:07 UTC. The burst was identified by both the Count-Rate Trigger and Image Trigger systems, with a significant signal-to-noise ratio of 58.13 in the 8-120 keV energy band, and was also detected by Fermi/GBM.

GCN-46071 — GRB 261029A · Thu, 29 Oct 2026 01:37:40 GMT
The Fermi Gamma-ray Burst Monitor (GBM) detected a likely long gamma-ray burst (GRB 261029A) on October 29, 2026, at 01:27:03 UT. The event was located at RA = 12.2, Dec = 32.3 (J2000) with a statistical uncertainty of 3.6 degrees, and the angle from the Fermi LAT boresight was 71.0 degrees.