GRB

Gamma-ray bursts (GRBs) are brief, intense flashes of gamma-ray photons originating from cosmological distances, followed by afterglows across the electromagnetic spectrum that can persist for days to weeks and beyond in X-ray, optical, and radio bands.

GRBs are commonly divided by duration into short GRBs (T90 less than about 2 seconds) and long GRBs (T90 greater than about 2 seconds). The two classes are associated with different progenitors: long GRBs are linked to the collapse of massive stars (collapsars) and are often accompanied by Type Ic supernovae, while short GRBs are thought to originate from mergers of compact objects such as neutron stars (or neutron star–black hole binaries). The prompt emission is highly variable and non-thermal, frequently modeled with a Band function, and the total energy can reach up to 10^52–10^54 erg if assumed isotropic; in reality the emission is beamed into narrow jets, reducing the true energy observed depending on the jet opening angle.

Afterglows arise from external shocks as the jet interacts with the surrounding medium, producing evolving emission across X-ray, optical, and radio wavelengths. Observations of afterglows enable precise localization and redshift measurements, revealing a redshift distribution that peaks around z ~ 2 and providing insights into star formation and early-universe conditions.

Historical milestones include the initial detection of GRBs in the late 1960s and the discovery of afterglows with BeppoSAX in 1997. The Swift and Fermi missions have since supplied rapid localizations and broad energy coverage, enhancing understanding of progenitors, jet physics, and the use of GRBs as probes of the distant universe. The joint detection of GRB 170817A with GW170817 established a direct link between short GRBs and neutron star mergers.