The Multiwavelength Approach to Unidentified Gamma-Ray Sources

As the highest-energy photons, gamma rays have an inherent interest to astrophysicists and particle physicists studying high-energy, nonthermal processes. Gamma-ray telescopes complement those at other wavelengths, especially radio, optical, and X-ray, providing the broad, mutiwavelength coverage that has become such a powerful aspect of modern astrophysics. Multiwavelength techniques of various types have been developed to help identify and explore unidentified gamma-ray sources. This overview summarizes the ideas behind several of these methods.Comment: Proceedings of the Conference "The Multiwavelength Approach to Unidentified Sources", to appear in the journal Astrophysics and Space Scienc

IDENTIFYING THE MYSTERIOUS EGRET SOURCES: SIGNATURES OF POLAR CAP PULSAR MODELS

The advent of the next generation of gamma-ray experiments, led by GLAST, AGILE, INTEGRAL and a host of atmospheric Čerenkov telescopes coming on line in the next few years, will enable ground-breaking discoveries relating to the presently enigmatic set of EGRET/CGRO UID galactic sources that have yet to find definitive identifications. Pulsars are principal candidates for such sources, and many are expected to be detected by GLAST, some that are radio-selected, like most of the present EGRET/Comptel pulsars, and perhaps even more that are detected via independent pulsation searches. At this juncture, it is salient to outline the principal predictions of pulsar models that might aid identification of gamma-ray sources, and moreover propel subsequent interpretation of their properties. This review summarizes relevant characteristics of the polar cap model, emphasizing where possible distinctions from the competing outer gap model. Foremost among these considerations are the hard X-ray to gamma-ray spectral shape, high energy cutoffs and pulse profiles, and how these characteristics generally depend on pulsar period and period derivative, as well as observational viewing angle. The polar cap model 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 agendas and parameter regimes for blind gamma-ray pulsation searches; examples include the highly-magnetized ones that are currently quite topical in astrophysics. 1 2 1