Pulse and Polarization Morphology for $\gamma$-Ray Pulsars

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Session 37 -- Pulsars
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[37.11] Pulse and Polarization Morphology for $\gamma$-Ray Pulsars

Roger W. Romani \& I.-A. Yadigaroglu (Stanford University)

The location and efficiency of pulsar $\gamma$-ray emission is a subject of appreciable debate. The variety of profiles found in recent EGRET detections motivates improved modeling. We present a calculation of polarization and profile properties of high energy pulsar emission in an outer gap picture. Our sums indicate that comparison with the polarization data and with radio pulse profiles provides significant constraints on the emission zone geometry. We find that high energy emission is generally detected from the pole opposite that associated with the surface radio pulse; the result is robust to uncertainties in the outer magnetosphere currents and details of the field geometry. The Crab pulsar provides an important test case and we match the model to optical polarization measurements tracing the outer gap region, as well as the high energy light curves. With spin axis inclinations and viewing geometries provided by the model fit, we derive an effective beaming factor that can be used to estimate the total flux from the detected value. We also show that this picture provides good correspondence to the $\gamma$-ray light curves and radio pulse offset and polarization properties for the other $\gamma$-ray pulsars ($e.g.$ PSR 1706-44, Geminga) and provides useful constraints on the emission altitude; these provide a clue to the origin of the spectral index variations in the $\gamma$-ray data.

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