Synchro-curvature radiation of charged particles in the strong curved magnetic fields

TL;DR

This paper introduces the synchro-curvature radiation regime, a hybrid of synchrotron and curvature radiation, showing its significance in strong curved magnetic fields and its implications for pulsar gamma-ray emission.

Contribution

The study provides an analytical framework for synchro-curvature radiation, highlighting its role in relativistic particle energy loss and gamma-ray emission in pulsar magnetospheres.

Findings

Identified the synchro-curvature regime as a significant radiation mode in strong magnetic fields.

Derived analytical expressions for radiation intensity and energy distribution.

Confirmed the importance of the regime through numerical simulations of particle energy losses.

Abstract

It is generally believed that the radiation of relativistic particles in a curved magnetic field proceeds in either the synchrotron or the curvature radiation modes. In this paper we show that in strong curved magnetic fields a significant fraction of the energy of relativistic electrons can be radiated away in the intermediate, the so-called synchro-curvature regime. Because of the persistent change of the trajectory curvature, the radiation varies with the frequency of particle gyration. While this effect can be ignored in the synchrotron and curvature regimes, the variability plays a key role in the formation of the synchro-curvature radiation. Using the Hamiltonian formalism, we find that the particle trajectory has the form of a helix wound around the drift trajectory. This allows us to calculate analytically the intensity and energy distribution of prompt radiation in the general case of magnetic bremsstrahlung in the curved magnetic field. We show that the transition to the limit of the synchrotron and curvature radiation regimes is determined by the relation between the drift velocity and the component of the particle velocity perpendicular to the drift trajectory. The detailed numerical calculations, which take into account the energy losses of particles, confirm the principal conclusions based on the simplified analytical treatment of the problem, and allow us to analyze quantitatively the transition between different radiation regimes for a broad range of initial pitch angles. We argue that in the case of realization of specific configurations of the electric and magnetic fields, the gamma-ray emission of the pulsar magnetospheres can be dominated by the component radiated in the synchro-curvature regime.