Is coherence essential to account for pulsar radio emission?

Abstract

Based on definitions, two joint criteria, namely the optically thin constraint and the energy budget constraint, are proposed to judge whether the emission nature of radio pulsars is incoherent or obliged to be coherent. We find that the widely accepted criterion, kTB η, is not a rational criterion to describe the optically 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) with emission power of a single particle as high as a critical value P ∼ 10^-4 to 10^-3 ergs s^-1. This in principle poses the possibility of interpreting high luminosities sing, c of pulsars in terms of incoherent emission mechanisms, if the optically thin constraint could be released by certain mechanisms as well. Coherence may not be an essential condition to account for pulsar radio emission.