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The Net Advance of Physics: Gamma-Ray Pulsar Emission Models, by Alice K. Harding -- Section 5.

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Polar cap and outer gap models have both evolved in order to

account for the observed emission features. Polar cap models now

assume that emission originates from only one magnetic pole and at

higher altitudes. Outer gap models must allow the gaps to extend

closer to the neutron star surface. The tex2html_wrap_inline167 -ray emission must be

either a hollow cone (CRPC and ICPC polar cap models) or a

curved fan beam (outer gap models) to produce double-peaked

profiles, bridge emission and the soft-hard-soft hardness variation;

however ICPC models do not predict emission outside the pulses.

CRPC models predicted high-energy spectral cutoffs (Daugherty &

Harding 1982) and a correlation of tex2html_wrap_inline167 -ray luminosity with

polar-cap current (Harding 1981), both of which have been

observed by CGRO. Outer gap models can also produce spectra

turnovers, but a luminosity-current correlation is not predicted.

Polar cap models predict an increase in spectral hardness with age;

outer gap models may predict this as well but it has not been

quantified. Outer gap models can more naturally account for phase

differences between tex2html_wrap_inline167 -ray and lower energy pulses if the lower

energy is assumed to come from near the surface. It is quite possible

that elements of all these models (and more) will be necessary

to account for the diverse features of tex2html_wrap_inline167 -ray pulsars.


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