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This introductory chapter presents the background story on the discovery and research on gamma-ray bursts (GRB). In 1963, Soviet Premier Nikita Khrushchev and U.S. President John F. Kennedy agreed to the Partial Test Ban Treaty. Ratifying nations agreed that all nuclear weapons testing would be conducted underground from then on: no longer would tests be conducted in oceans, in the atmosphere, or in space. The United States, led by a team at the Los Alamos National Laboratory, promptly began the ambitious Vela Satellite Program to test for “non-compliance” with the Treaty. Not long after Los Alamos employee Ray Klebesadel began detecting GRBs. In 1973, Klebesadel and his colleagues Ian Strong and Roy Olson published a paper entitled “Observations of Gamma-Ray Bursts of Cosmic Origin” the Astrophysical Journal, which marked the beginning of the GRB enigma that to this day captivates the imagination and keeps astronomers scratching their heads.

This chapter discusses the definition, emission, and central engine of gamma-ray bursts (GRBs). Before the afterglow era, GRBs were essentially defined by observations of their high-energy emission. The landscape of such observations—the light curves and spectra of the events—exhibits at once great diversity and elements of commonality that bind different events together. GRBs are like fingerprints: no two are alike, but they share common properties. Those common elements provide strong constraints both on the nature of the “engine” that supplies the energy to the event and the physical processes that drive the emission we see. Since the 1990s, GRB monitors in space have observed more than one hundred GRBs. Since 2004, the NASA GRB satellite called Swift has been discovering GRBs at a rate of about two per week.

This chapter focuses on the search for afterglows of gamma-ray bursts (GRBs). In 1996, Peter Mészáros (Pennsylvania State University) and Martin J. Rees (Cambridge University) began developing a detailed theory of afterglows, positing that long-lived emission should be observed at all wavelengths—a panchromatic phenomenon—as a natural consequence of synchrotron emission from a decelerating blastwave. Though no convincing afterglow had been found to date, the afterglow revolution beginning the following year would quickly confirm the basic theory. The chapter presents the panchromatic observations of GRB afterglows and then discusses afterglow theory and its significant modifications over the years.

The sources of short gamma ray bursts (GRBs) have been identified with neutron star merger events. Hulse and Taylor discovered the first binary neutron star in 1974. By monitoring the pulsar in this system the orbital characteristics of the system have been determined with great accuracy. This has led to tests of general relativity, including the first confirmation of the existence of gravitational waves. The emission of this radiation is gradually bringing the two neutron stars together. They will collide and merge in about 300 million years.