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