gamma-ray burst

A gamma-ray burst (GRB) is a short flash of gamma rays, lasting from a few milliseconds to several minutes, often followed by an afterglow (GRB afterglow) of longer-wavelength radiation. Roughly half are accompanied by an optical transient (GRB optical transient), the others being termed dark bursts. Some show such extreme energy that it is presumed that the source emits them directionally, i.e., they cannot be from an isotropic emission. GRBs were first detected in 1967 by satellites intended to detect nuclear weapons tests (the Vela satellites). A significant part of gamma-ray astronomy is detection and study of the bursts, and gamma-ray observatory satellites have invariably included burst detectors. Presumed sources (GRB progenitors, gamma-ray burst progenitors) include supernovae, magnetars, and/or mergers of neutron stars. The latter is theorized as a cause of short gamma-ray bursts (SGRBs), which last on the order of a fraction of a second. Superluminous supernovae are theorized to create long gamma-ray bursts (LGRBs), which last on the order of 30 seconds. A threshold time-length of 2 seconds is generally used to nominally classify GRBs as one or the other type. Thus GRB light curves are part of their study. The term GBS for gamma-ray burst source or gamma burst source used for bodies such as pulsars presumed to be sources. Some bursts have been termed FRED GRBs for fast rise exponential decay GRBs.

An orphan afterglow (orphan GRB afterglow) is the appearance of an afterglow like that of a GRB but not subsequent to an apparent GRB. The presumption is that the GRB gamma rays are highly beamed but the afterglow spreads a bit wider, so we can observe the afterglow of some GRBs that miss us. Afterglows appear to be synchrotron radiation, and are attributed to the beamed explosion, which can be described as a jet.

GRBs remain of current research interest and much progress is now being made with recent efforts and technology and the above descriptions may be a bit out-of-date.