Model of pulsar pair cascades in non-uniform electric fields: Growth rate, density profile, and screening time

Abstract

Time-dependent cascades of electron–positron pairs are thought to be the main source of plasma in pulsar magnetospheres and a primary ingredient to explain the nature of pulsar radio emission, a long-standing open problem in high-energy astrophysics. During these cascades—positive feedback loops of gamma-ray photon emission via curvature radiation by TeV electrons and positrons and pair production—the plasma self-consistently develops inductive waves that couple to electromagnetic modes capable of escaping the pulsar dense plasma. In this work, we present an analytical description of pair cascades relevant in pulsars, including their onset, exponential growth, and saturation stages. We study this problem in the case of a background linear electric field, relevant in pulsar polar caps, and using an heuristic model of the pair production process. The analytical results are confirmed with particle-in-cell simulations performed with the OSIRIS code that include heuristic pair production.