Pulsed gamma-ray emission from short-period pulsars

Abstract

We study the gamma-ray emission mechanisms from pulsars with period, P, between 4.6 × 10-2B2/5 12 s and 0.17B5/12 sin1/6 θα-5/4 s in terms of outermagnetospheric gap model, in which electrostatic accelerators have been proposed to exist in regions near the null charge surfaces where Ω· B = 0. We found that the spectra of all known γ-ray pulsars can be fitted by two free parameters, namely, αrL, the mean distance to the outergap, and sin Eθ, the mean pitch angle of the secondary e± pairs. Gamma-rays from those pulsars with P < 0.17B5/12 sin1/6 θα-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 ∼10-2. For pulsars with period approaching ∼0.17B5/12 sin1/6 θα-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.