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Introduction
Gamma-ray bursts were serendipitously discovered in 1967 by the
Vela satellites
\cite{Klebesadel_1973}. Designed to verify compliance with the 1963 Partial Test Ban Treaty signed with the Soviet Union, the satellites were configured to search for evidence of nuclear testing in space and (later) the upper atmosphere. While with one possible exception (the
Vela Incident) no evidence for testing nuclear weapons was uncovered, the satellites did uncover short-duration flashes of high-energy radiation that were not consistent with the location of the Sun or the Earth.
These flashes, subsequently dubbed gamma-ray bursts (GRBs), are characterized by the following observational properties:
- Short duration, dt ~0.1-100 s
- Variability on time scales as short as ms
- Non-thermal spectra, with peak energy output ~ few hundred keV
- Non-repeating
- Extremely bright (fluences ~ 10-4 erg s-1; outshining the entire gamma-ray sky)
A representative sample of light curves of GRBs is shown in Figure 1.