Particle acceleration to PeV energies in Pulsar Wind Nebula: a two zone model

TL;DR

This paper presents a two-zone magnetohydrodynamics model of pulsar wind nebulae, demonstrating conditions under which they can accelerate particles to PeV energies, and compares predictions with recent LHAASO observations.

Contribution

It introduces a simplified MHD-based model linking nebular parameters to particle acceleration, highlighting the roles of magnetization and turbulence in PeV acceleration.

Findings

Low magnetization parameter $\sigma$ favors PeV acceleration.

Turbulence enhances particle acceleration to PeV energies.

Model successfully explains observations of two LHAASO PeVatrons.

Abstract

\textit{PeVatrons} are the extreme galactic accelerators capable of producing PeV particles. Recent observation of Large High Altitude Air Shower Observatory have detected UHE photons ($\geq$ 100 TeV) from 43 galactic sources. Detection of UHE photons demands the presence of at least PeV particles in the acceleration site. Although the exact nature of most of the sources are still unknown, a large fraction of these sources have spatial association with pulsar wind nebula. In this work we investigate the acceleration mechanism in pulsar wind nebula by following a magnetohydrodynamics approach. Current study relates the MHD flow solution in immediate downstream with the particle spectrum and spectral energy distribution of photons. Our study shows that MHD description in the PWN environment reduces the parameter space and most of the parameters can be constrained in terms of a single parameter, \textit{the magnetization parameter} $\sigma$ only. Considering the effect of $\sigma$, we show that in low $\sigma$ environment pulsar wind nebula can produce PeV particles. We have also investigate the role of turbulence in the nebular region in acceleration of particle to PeV energy. Current study shows that both low $\sigma$ environment and turbulence environment is favorable for acceleration of particles up to PeV energy. We have also tested our model in two different LHAASO detected PeVatron 1LHAASO J1848-000u and 1LHAASO J1929+1846u.