Inverse Compton model of pulsar high energy emission

TL;DR

This paper models the Crab pulsar's broad spectrum from UV to gamma-rays using a cyclotron-self-Compton framework, highlighting inverse Compton scattering as a key high-energy emission process.

Contribution

It introduces a comprehensive model explaining pulsar high-energy emission through counter-streaming beams and Klein-Nishina regime scattering, linking radio to gamma-ray emissions.

Findings

Reproduces Crab pulsar spectrum over ten energy decades.

Identifies inverse Compton scattering as dominant high-energy mechanism.

Suggests outer gaps as significant pair production sites.

Abstract

We reproduce the broadband spectrum of Crab pulsar, from UV to very high energy gamma-rays - nearly ten decades in energy, within the framework of the cyclotron-self-Compton model. Emission is produced by two counter-streaming beams within the outer gaps, at distances above $\sim$ 20 NS radii. The outward moving beam produces UV-$X$-ray photons via Doppler-booster cyclotron emission, and GeV photons by Compton scattering the cyclotron photons produced by the inward going beam. The scattering occurs in the deep Klein-Nishina regime, whereby the IC component provides a direct measurement of particle distribution within the magnetosphere. The required plasma multiplicity is high, $\sim 10^6-10^7$, but is consistent with the average particle flux injected into the pulsar wind nebula. The importance of Compton scattering in the Klein-Nishina regime also implies the importance of pair production in the outer gaps. We suggest that outer gaps are important sources of pairs in pulsar magnetospheres. Cyclotron motion of particles in the pulsar magnetosphere may be excited due to coherent emission of radio waves by streaming particles at the anomalous cyclotron resonance. Thus, a whole range of Crab non-thermal emission, from coherent radio waves to very high energy $\gamma$-rays - nearly eighteen decades in energy - may be a manifestation of inter-dependent radiation processes. The present model, together with the observational evidence in favor of the IC scattering (Lyutikov et al. 2012; Lyutikov 2012), demonstrates that the inverse Compton scattering can be the dominant high energy emission mechanism in majority of pulsars.