Gamma-Ray Bursts

Gamma-ray bursts (GRBs) are short bursts of high-energy radiation from an unpredictable location in the sky. The γ-ray emission can rise to maximum intensity within fractions of a millisecond. During these short times GRBs are the brightest objects in the γ-ray sky. The energy spectra are nonthermal, with most of the power radiated in the 100–500 keV range, but photons up to 18 GeV or down to a few kiloelectronvolt have also been registered. The bursts have durations of typically 0.1–100 s, with a bimodal distribution separating “short” and “long” duration GRBs at ∼1–2s [57] with a relative occurrence of 1:4 [49]. In addition, short bursts are typically harder than the long bursts, supporting the conjecture that they form two classes of object (Fig. 24.1).