High-Energy Emission from Pulsars: the Polar Cap Scenario

Pulsar astronomy is at a fascinating juncture with many exciting new results from the Chandra and XMM X-ray telescopes, and the prospects of next generation gammaray experiments, led by space missions GLAST, AGILE, INTEGRAL and a number of atmospheric Cerenkov telescopes coming on line in the next few years. These will enable a continuation of ground-breaking discoveries. Pulsars are expected to be detected by GLAST in profusion, some that are radio-selected, like most of the present EGRET/Comptel pulsars, and perhaps even more that are detected via independent pulsation searches. This theoretical review summarizes relevant characteristics of the polar cap model, emphasizing distinctions from the competing outer gap model. These features include principal acceleration properties, the X-ray to gamma-ray spectral shape, high energy cutoffs, pulse profiles and flux observabilities in different wavebands, and how these characteristics generally depend on pulsar period and period derivative, as well as observational orientation. The polar cap scenario exhibits definitive signatures that will be readily tested by the detections of GLAST and other experiments, thereby establishing cogent observational diagnostics. The paper focuses on different classes of pulsars that might define distinct science agendas; examples include millisecond pulsars, the highly-magnetized ones/magnetars that are currently quite topical in astrophysics, and older ones proximate to putative death lines.