Is Coherence Essential to Account for Pulsar Radio Emission?

Abstract

Based on definitions, two joint-criteria, namely, the optical-thin constraint and the energy budget constraint, are proposed to judge whether the emission nature of radio pulsars is incoherent or obligatory to be coherent. We find that the widely accepted criterion, $kT_B \le ε$, is not a rational criterion to describe the optical-thin condition, even for the simplest case. The energy budget constraint could be released by introducing a certain efficient radiation mechanism (e.g. the inverse Compton scattering, QL98) with emission power of a single particle as high as a critical value $P_{sing,c} \sim 10^{-4}-10^{-3} {erg s}^{-1}$. This in principle poses the possibilities to interpret high luminosities of pulsars in terms of incoherent emission mechanisms, if the optical-thin constraint could be released by certain mechanism as well. Coherence may not be an essential condition to account for pulsar radio emission.