Nonthermal emission model of isolated X-ray pulsar RX J0420.0-5022

TL;DR

This paper proposes a nonthermal synchrotron emission model for the X-ray spectrum of the isolated pulsar RX J0420.0-5022, explaining observed emissions through cyclotron instability and quasi-linear diffusion mechanisms.

Contribution

It introduces a novel nonthermal synchrotron emission model based on cyclotron instability and QLD, providing an alternative to thermal emission models for this pulsar.

Findings

The spectral energy distribution matches observational data well.

The model fits the X-ray spectrum better than black-body models.

Optical and X-ray emissions are explained by the proposed mechanism.

Abstract

In the present paper an alternative theoretical interpretation to the generally assumed thermal emission models of the observed X-ray spectrum of isolated pulsar RX J0420.0-5022 is presented. It is well known that the distribution function of relativistic particles is one-dimensional at the pulsar surface. However, cyclotron instability causes an appearance of transverse momenta of relativistic electrons, which as a result, start to radiate in the synchrotron regime. On the basis of the Vlasov's kinetic equation we study the process of the quasi-linear diffusion (QLD) developed by means of the cyclotron instability. This mechanism provides generation of optical and X-ray emission on the light cylinder lengthscales. The analysis of the three archival XMM-Newton observations of RX J0420.0-5022 is performed. Considering a different approach of the synchrotron emission theory, the spectral energy distribution is obtained that is in a good agreement with the observational data. A fit to the X-ray spectrum is performed using both the present synchrotron emission model spectrum absorbed by cold interstellar matter and generally assumed absorbed black-body model.