The Net Advance of Physics: Gamma-Ray Pulsar Emission Models, by Alice K. Harding -- Section 2.

Observed Patterns

There are several patterns and correlations that show up in recent

CGRO data which the existing models must be able to explain (see

the review by Thompson (1996) for a more complete discussion of

the observations). Briefly, these are:

1) Light curves having double peaks (most widely separated) with bridge emission are common.

2) The spectral hardness shows a systematic variation through the profile that is a maximum in the bridge region (Fierro et al. 1996).

3) The hardness of the phase-averaged spectrum increases with age (i.e. (Thompson et al. 1994).

4) All pulsars show high energy breaks or cutoffs in their spectrum (Nel & DeJager 1995).

5) There is a correlation between -ray luminosity and polar-cap current (or open field-line voltage) .

Despite these remarkable regularities, there are some puzzling

misfits and lack of pattern. Except for the Crab, where there is

almost complete alignment of the pulse phase across all

wavelengths, there is no alignment of the -ray pulses with the

light curves at other wavebands. All of the spectral cutoffs occur

above 1 GeV, except in PSR1509-58, where the cutoff occurs

between 4 and 30 MeV. PSR0656+14 is the one exception to the

-ray luminosity-polar cap current correlation. Geminga is the

only -ray pulsar that is not a radio pulsar.

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