Long GRB 260208A detected by Fermi at z=2.36 with multi-wavelength follow-up

AI Summary

Fermi GBM detected a long gamma-ray burst (GRB 260208A, trigger 792220053) on 2026-02-08 at 05:07:28 UT with a duration of ~35.3 seconds and peak flux of 29.7 ph/s/cm². The burst was also detected by Fermi-LAT (highest energy photon: 5.3 GeV), GECAM-B, NuSTAR, and ground-based gamma-ray instruments. Spectroscopic observations with NOT determined a redshift of z=2.36, placing the source at ~11.5 billion light-years. Extensive multi-wavelength follow-up confirmed the optical afterglow (AT 2026ciw) with initial magnitude ~15.2, X-ray detection by Swift-XRT, and radio detection by VLA at 2 days post-burst.

Notices (1)

Fermi — GRB · Sat, 07 Feb 2026 23:37:28 GMT

GCN Circulars (26)

GCN-43952 — GRB 260208A · Tue, 10 Mar 2026 09:40:09 GMT
The Karl G. Jansky Very Large Array (VLA) detected an unresolved radio source at the position of GRB 260208A, consistent with previous X-ray and optical observations. The preliminary results indicate peak flux densities of 59 uJy/b at 6 GHz, 90 uJy/b at 10 GHz, and 125 uJy/b at 15 GHz.

GCN-43896 — GRB 260208A · Mon, 02 Mar 2026 15:52:13 GMT
The TERI gamma-ray telescope on the International Space Station has detected GRB 260208A, which was also observed by multiple other telescopes. The burst had an onset at 2026-02-08T05:07:28 and three emission peaks with excess counts per second above the baseline rate. The analysis is preliminary and lacks a detailed response function. TERI is a technology demonstrator for large-volume pixelated CdZnTe detectors developed by the U.S. Naval Research Laboratory and H3D, Inc.

GCN-43771 — GRB 260208A · Tue, 17 Feb 2026 14:19:08 GMT
The IKI-GRB-FuN team reported non-detection of the optical counterpart of GRB 260208A using the 0.7-meter AS-32 telescope at AbAO and the 2-meter Zeiss-2000 telescope at Terskol. The team did not detect any emission in the stacked frames taken on February 10, 2026. The preliminary photometry shows upper limits of 20.4 mag for AbAO and 21.2 mag for Terskol.

GCN-43770 — GRB 260208A · Tue, 17 Feb 2026 14:07:31 GMT
Astronomers at IKI RAS report the detection of the optical counterpart of GRB 260208A using the AZT-33IK 1.5m telescope at Mondy observatory on February 9, 2026. The object was not detected on February 10. Preliminary magnitude measurement was 21.58 with an uncertainty of 0.1 mag.

GCN-43694 — GRB 260208A · Wed, 11 Feb 2026 12:33:24 GMT
Astronomers using the Las Cumbres Observatory (LCO) detected the optical counterpart of the long and bright gamma-ray burst (GRB) 260208A, which was previously detected by various satellites. The optical counterpart, AT 2026ciw, was observed about 26.7 hours after the gamma-ray trigger and had an AB magnitude of r' = 20.92 +/- 0.17. The redshift of the GRB is z = 2.36.

GCN-43675 — GRB 260208A · Mon, 09 Feb 2026 23:42:07 GMT
The International Space Station's Glowbug gamma-ray telescope, operated by the US Naval Research Laboratory, detected GRB 260208A, a gamma-ray burst also observed by several other telescopes. The burst had a duration of 53.2 seconds and a total significance of about 369 sigma. The preliminary analysis suggests a triple-peaked structure in the light curve.

GCN-43674 — GRB 260208A · Mon, 09 Feb 2026 21:01:46 GMT
The NuSTAR SINGS working group has detected prompt emission from long-duration GRB 260208A using NuSTAR CsI shield data. The detection occurred approximately 5 seconds after the GRB was identified by Fermi/GBM and GECAM-B. The NuSTAR data reveals a peak count rate of ~4500 cps with a baseline rate of ~1000 cps, and marginal evidence of emission above 100 keV. The optical counterpart of the GRB is located 99 degrees off the NuSTAR boresight and 111 degrees off the geocenter.

GCN-43673 — GRB 260208A · Mon, 09 Feb 2026 20:09:35 GMT
On 08 February 2026, the Fermi Gamma-ray Burst Monitor (GBM) detected a gamma-ray burst (GRB 260208A) with a duration of approximately 35.3 seconds and a redshift of 2.36. The burst was also detected by Fermi-LAT, Swift XRT, and NOT. Preliminary spectral analysis reveals a power law function with an exponential high-energy cutoff, with a power law index of -0.87 and a cutoff energy of 460 keV. The event fluence in the 10-1000 keV band is (1.50 +/- 0.06)E-04 erg/cm^2, and the peak photon flux is 29.7 +/- 0.4 ph/s/cm^2. Final results will be published in the Fermi GBM Catalog.

GCN-43667 — GRB 260208A · Mon, 09 Feb 2026 12:00:08 GMT
Astronomers at IKI RAS, led by A. Volnova, report the detection of the optical counterpart of GRB 260208A using the AZT-33IK 1.5m telescope at Mondy observatory. The team obtained R-band observations on February 8, 2026, and measured a magnitude of 19.92 with an uncertainty of 0.06. The photometry is based on nearby SDSS stars and is not corrected for Galactic extinction.

GCN-43666 — GRB 260208A · Mon, 09 Feb 2026 11:57:27 GMT
Astronomers from IKI RAS, ISTP, and IKI-GRB-FuN reported the detection of the optical counterpart of GRB 260208A using the AZT-33IK 1.5m telescope at Mondy observatory. The team obtained preliminary R-band magnitudes of 19.92, 20.14, and 20.05 with errors of 0.06 and 0.07, and no Galactic extinction correction was applied.

GCN-43665 — GRB 260208A · Mon, 09 Feb 2026 11:24:07 GMT
The ARIES team reports the optical detection of GRB 260208A using the 1.3m Devasthal Fast Optical Telescope (DFOT) 15.75 hours after the gamma-ray burst was first detected. The team obtained a preliminary magnitude of 19.89 +/- 0.04 in a single R-band exposure.

GCN-43664 — GRB 260208A · Mon, 09 Feb 2026 11:14:54 GMT
Astronomers using the DDRAGO imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional in Mexico have detected the optical counterpart of the gamma-ray burst GRB 260208A, located at a redshift of 2.36. The team obtained 30 minutes of simultaneous exposure in the r and z filters and measured preliminary magnitudes of r = 21.09 ± 0.04 and z = 20.64 ± 0.06.

GCN-43662 — GRB 260208A · Mon, 09 Feb 2026 10:13:18 GMT
A team of astronomers led by A. de Ugarte Postigo et al. report the observation of GRB 260208A's optical counterpart, AT2026ciw, using the NOT and other telescopes. The preliminary spectrum analysis indicates a redshift of z = 2.36, suggesting a distance of approximately 11.5 billion light-years. The detection of various absorption features supports this measurement.

GCN-43661 — GRB 260208A · Mon, 09 Feb 2026 10:00:09 GMT
A team of astronomers led by the University of Birmingham reported the detection of the optical counterpart of GRB 260208A using the IO:O camera on the 2m robotic Liverpool Telescope 22.8 hours after the gamma-ray burst trigger. The team measured an AB magnitude of 20.63 ± 0.04 for the counterpart in both SDSS r and i filters.

GCN-43658 — GRB 260208A · Mon, 09 Feb 2026 05:50:39 GMT
GRB 260208A, detected by Fermi/GBM and Fermi/LAT, was observed by GECAM-B and localized to a position in the sky with a duration of 38 +- 2 seconds and a time-averaged energy flux of (1.62 +- 0.056)E-04 erg/cm^2. The burst's time-averaged spectrum was best fit by a power law function with an exponential high-energy cutoff at 651 +- 134 keV, consistent with Type I GRBs in the Amati relation diagram.

GCN-43657 — GRB 260208A · Mon, 09 Feb 2026 03:44:52 GMT
Astronomers using the Zwicky Transient Facility (ZTF) at Palomar Observatory have detected the afterglow of a gamma-ray burst (GRB 260208A) observed by the Fermi satellite. The team obtained g- and r-band images covering 130 square degrees, identifying the afterglow candidate AT 2026ciw (ZTF26aafswob) as the only source passing their filtering scheme. The observations were made using the Samuel Oschin Telescope 48-inch and 60-inch Telescope at Palomar Observatory, supported by the National Science Foundation and a partnership of universities and institutions.

GCN-43655 — GRB 260208A · Mon, 09 Feb 2026 02:31:49 GMT
The Space Variable Objects Monitor (SVOM) team reports a successful Target of Opportunity observation of GRB 260208A using the VT instrument. The optical counterpart was detected in both VT_B and VT_R bands, with magnitudes of 21.15 ± 0.06 and 20.40 ± 0.04, respectively. The observation began 8.842 hours after the gamma-ray burst was detected by Fermi/GBM and Fermi/LAT.

GCN-43652 — GRB 260208A · Sun, 08 Feb 2026 21:51:33 GMT
The Swift-XRT team reported observing and detecting a new X-ray source, Source 1, located 2.2 arcsec from the new optical source of the Fermi/LAT-detected gamma-ray burst GRB 260208A. The X-ray source has a count-rate of 0.0488 +/- 0.0045 ct s^-1 and a flux of (1.55 +/- 0.14)e-12 erg cm^-2 s^-1 in the 0.3-10 keV range. The team could not yet determine if the source is fading.

GCN-43645 — GRB 260208A · Sun, 08 Feb 2026 15:21:39 GMT
On February 8, 2026, at 05:07:28.24 UT, GRB 260208A was detected by Fermi-LAT, producing a significant increase in event rate with a photon flux of (2.86 ± 0.65)E-6 ph/cm2/s above 100 MeV. The highest-energy photon, with an energy of 5.3 GeV, was observed 1168 seconds after the initial GBM trigger. The event occurred at RA, Dec = 204.57, 33.77 (J2000) with an error radius of 0.15 deg.

GCN-43643 — GRB 260208A · Sun, 08 Feb 2026 14:50:32 GMT
Swift observatory initiated a Target of Opportunity (ToO) observation of gamma-ray burst (GRB) 260208A, which was first detected by Fermi/LAT. The X-ray data from the observation will be analyzed and any uncatalogued X-ray sources will be reported online and via GCN COUNTERPART notices. Probable afterglow candidates will be reported via GCN Circulars.

GCN-43642 — GRB 260208A · Sun, 08 Feb 2026 14:07:05 GMT
A misclassified Fermi Gamma-ray Burst (GRB) event, identified as 260208A, has been corrected. The initial classification as a particle trigger was in error, and the true GRB location and detection by the MASTER optical telescope have been confirmed.

GCN-43641 — GRB 260208A · Sun, 08 Feb 2026 14:01:53 GMT
The Gravitational-wave Optical Transient Observer (GOTO) collaboration reported the detection of a potential optical counterpart to the gamma-ray burst (GRB) 260208A using their network of telescopes. The source, designated GOTO26aob, was detected at an L-band magnitude of 13.78 ± 0.01 AB mag 20 minutes after the GRB trigger and faded to a magnitude of 16.72 ± 0.01 AB mag after 1.36 hours. No evidence of the source was found in previous GOTO observations taken 1.57 hours before the trigger, down to a 5-sigma depth of L>19.07 AB mag.

GCN-43640 — GRB 260208A · Sun, 08 Feb 2026 12:35:14 GMT
The MASTER Global Robotic Net has discovered a bright optical transient, designated as MASTER OT J133855.59+334806.2, inside the retracted error-box of the Fermi GRB 260208A. The transient was detected using the MASTER-OAFA system and has an unfiltered magnitude of 15.2. Previous observations from 2019 reveal a reference magnitude of 20.7. Deep photometry and spectral observations are required for further analysis.

GCN-43637 — GRB 260208A · Sun, 08 Feb 2026 06:45:32 GMT
The MASTER-OAFA robotic telescope in Argentina observed Fermi GRB 260208A, reporting upper limits on magnitudes ranging from 15.2 to 17.9 in clear band, 866 seconds after the trigger time.

GCN-43636 — Fermi Gamma-ray Burst Monitor trigger 792220053/260208214 is not a GRB · Sun, 08 Feb 2026 06:13:21 GMT
Fermi Gamma-ray Burst Monitor trigger 792220053/260208214, initially classified as a gamma-ray burst (GRB) on February 8, 2026, has been identified as not being a GRB but rather caused by distant particles.

GCN-43635 — GRB 260208A · Sun, 08 Feb 2026 05:18:10 GMT
The Fermi Gamma-ray Burst Monitor (GBM) has detected and located a Long Gamma-ray Burst (GRB), designated as GRB 260208A, at a position RA = 204.4, Dec = 33.0 (J2000 degrees) with a statistical uncertainty of 1.0 degrees. The angle from the Fermi Large Area Telescope (LAT) boresight is 79.0 degrees. This event is significant as gamma-ray bursts are among the most powerful explosions in the universe and provide valuable insights into the nature of the universe.