GRB 251222A

General information

GRB 251222A is a long-duration gamma-ray burst detected by Fermi/GBM and SVOM (ECLAIRs), with an X-ray/optical/radio afterglow reported by multiple facilities. A spectroscopic redshift of z = 3.171 was measured for the afterglow/host line of sight.

Wavelength coverage

• Gamma-ray: Prompt emission reported by Fermi/GBM and Konus-Wind; additional high-energy detections noted by SVOM/ECLAIRs and GECAM-B.
• X-ray: Swift/XRT detected an uncatalogued fading X-ray source consistent with the afterglow position; EP instruments are referenced in association.
• Optical/NIR: Extensive optical follow-up (multiple filters) including early-time evolution and later monitoring; NIR detections include J-band.
• Radio: VLA detection at 6, 10, and 15 GHz at ~1.5 days post-burst. No observations were mentioned for: UV spectroscopy/photometry, millimeter/submillimeter, TeV gamma-rays.

Lightcurve and spectrum

• Prompt duration: T90 ~83 s (50–300 keV; Fermi/GBM).
• Prompt spectral models/params: Fermi/GBM reports a cutoff power-law fit with index ~-1.26 and Epeak ~118 keV (Band fit also acceptable); Konus-Wind CPL fits give Ep ~102–131 keV with alpha ~-1.45 to -1.23.
• Prompt fluence: (1.09 ± 0.02)×10^-5 erg/cm^2 (10–1000 keV; Fermi/GBM); Konus-Wind reports (9.92 ± 0.94)×10^-6 erg/cm^2 (20 keV–10 MeV).
• X-ray afterglow: Swift/XRT light curve modeled with power-law decay index alpha ~1.9; XRT spectrum consistent with an absorbed power law with photon index ~1.92.
• Optical behavior: Early rise to a peak followed by fading, with reported rebrightening/bumps (e.g., bump around ~500 s and another around ~10 ks in some optical monitoring); a reported R-band temporal index of ~-0.64 from a power-law fit (one dataset).
• Radio: VLA detects an unresolved source at 6/10/15 GHz with peak flux densities of ~71/208/241 µJy/beam at ~1.48 days.

Redshift

z = 3.171 (spectroscopic; VLT/X-shooter absorption features including a Lya trough and multiple metal lines).

What’s special vs typical

• Secure high-redshift (z=3.171) long GRB with broad community follow-up, including a radio detection and detailed prompt/afterglow characterization.
• Reported structured optical evolution (early rise/decay plus rebrightening/bumps) that is more complex than a single smooth power-law decay.