On particle acceleration and very high energy γ-ray emission in Crab-like pulsars

¹ E. Kharadze Georgian National Astrophysical Observatory, Ilia Chavchavadze State University, Kazbegi str. 2a, 0106 Tbilisi, Georgia e-mail: z.osmanov@astro-ge.org
² Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany e-mail: frank.rieger@mpi-hd.mpg.de
³ European Associated Laboratory for Gamma-Ray Astronomy, jointly supported by CNRS and MPG, Germany

Received: 18 March 2009
Accepted: 18 May 2009

Abstract

Context. The origin of very energetic charged particles and the production of very high-energy (VHE) gamma-ray emission remains still a challenging issue in modern pulsar physics.

Aims. By applying a toy model, we explore the acceleration of co-rotating charged particles close to the light surface in a plasma-rich pulsar magnetosphere and study their interactions with magnetic and photon fields under conditions appropriate for Crab-type pulsars.

Methods. Centrifugal acceleration of particles in a monopol-like magnetic field geometry is analyzed and the efficiency constraints, imposed by corotation, inverse Compton interactions and curvature radiation reaction are determined. We derive expressions for the maximum particle energy and provide estimates for the corresponding high-energy curvature and inverse Compton power outputs.

Results. It is shown that for Crab-like pulsars, electron Lorentz factor up to γ ~ 10⁷ can be achieved, allowing inverse Compton (Klein-Nishina) up-scattering of thermal photons to TeV energies with a maximum luminosity output of ~10³¹ erg/s. Curvature radiation, on the other hand, will result in a strong GeV emission output of up to ~ erg/s, quasi-exponentially decreasing towards higher energies for photon energies below ~50 GeV.

Conclusions. Accordingly to the results presented only young pulsars are expected to be sites of detectable VHE γ-ray emission.