PULSED GAMMA-RAY EMISSION FROM SHORT-PERIOD PULSARS

We study the gamma-ray emission mechanisms from pulsars with period, P, between 4.6 x 10(-2)B-12(2/5) s and 0.17B-5/12 sin1/6 thetaalpha-5/4 s in terms of outermagnetospheric pp model, in which electrostatic accelerators have been proposed to exist in regions near the null charge surfaces where OMEGA . B = 0. We found that the spectra of all known gamma-ray pulsars can be fitted by two free parameters, namely, alphar(L), the mean distance to the outergap, and sin theta, the mean pitch angle or the secondary e+/- pairs. Gamma-rays from those pulsars with P < 0.17B5/12 Sin1/6 thetaalpha -5/4 are mainly emitted by secondary e+/- pairs, which are created beyond the outergap, via synchrotron radiation and the gamma-ray emission efficiency is approximately 10(-2). For pulsars with period approaching -0.17B5/12 sin1/6 thetaalpha-5/4 s, their gamma-ray emission efficiency is approaching unity. The comparison of model results and the observed data, including gamma-ray spectrum, efficiency, relative intensity, and phase separation of pulses are discussed in the text.