Particle acceleration by pulsar wind nebulae inside supernova remnants

Abstract

The origin of cosmic-ray (CR) PeVatrons is a long standing problem. The CR spectrum breaks at about 1 PeV (so called, the knee energy). The diffusive shock acceleration at supernova remnants (SNRs) is believed to be the acceleration mechanism of CRs up to the knee energy. However, it was estimated that SNRs cannot accelerate CRs to the knee energy without magnetic field amplification. In this study, we propose that CR PeVatrons are pulsar wind nebulae (PWNe) inside SNRs. After a core-collapse supernova explosion, the PWN initially expands into the freely expanding supernova ejecta. Thereafter, the PWN catches up with the reverse shock of the SNR, where particles can be slightly accelerated by the back and forth motion between the PWN and the SNR, and some particles diffuse into the PWN. Afterwards the PWN is compressed by the SNR, where the particles in the PWN are accelerated by the adiabatic compression. Using a Monte Carlo simulation, we show that particles accelerated by the SNR to $0.1~{¥rm PeV}$ can be reaccelerated to $1~{¥rm PeV}$ until the end of the PWN compression.