Gamma-Ray Pulsars

Abstract

In 1967 a new radio telescope was commissioned in England. A group of astronomers under the direction of Anthony Hewish at the University of Cambridge had completed this receiver system to study the newly discovered quasi stellar radio sources and the rapid scintillations that result when radio waves from distant cosmic point sources pass through the turbulent interstellar and interplanetary plasma. One goal was to study the properties of these cosmic plasma clouds, and the sensitive receiver at 81.5 MHz was therefore fitted with a high-speed recorder. The intensity of celestial sources passing over the fixed field of radio receivers was recorded on strip charts and had to be analyzed by visual inspection. This task fell naturally to the graduate student of the group, Jocelyn Bell. On August 6, 1967, she first noticed a peculiar train of radio signals when the sky at right ascension 19hl9min passed through the field of view. What could have caused such a transient periodic signal? The first suspicion was of course interference from some electric equipment, like the ignition of a passing car or a satellite. But to the surprise of Bell the signal appeared again at about the same time of day.