# Nonlinear QED effects in X-ray emission of pulsars

## TL;DR

This paper investigates how strong magnetic fields near pulsars induce nonlinear QED effects that alter X-ray photon polarization, predicting observable signatures for upcoming X-ray polarimetry missions.

## Contribution

It models the polarization evolution of X-ray photons in pulsar magnetospheres using the Euler-Heisenberg Lagrangian, revealing significant circular polarization effects.

## Key findings

- Linearly polarized X-ray photons can develop high circular polarization.
- Polarization characteristics depend on pulsar magnetic field, inclination, and rotation.
- Predictions are testable with future X-ray polarimetric observations.

## Abstract

In the presence of strong magnetic fields near pulsars, the QED vacuum becomes a birefringent medium due to nonlinear QED interactions. Here, we explore the impact of the effective photon-photon interaction on the polarization evolution of photons propagating through the magnetized QED vacuum of a pulsar. We solve the quantum Boltzmann equation within the framework of the Euler-Heisenberg Lagrangian to find the evolution of the Stokes parameters. We find that linearly polarized X-ray photons propagating outward in the magnetosphere of a rotating neutron star can acquire high values for the circular polarization parameter. Meanwhile, it is shown that the polarization characteristics of photons besides photon energy depend strongly on parameters of the pulsars such as magnetic field strength, inclination angle and rotational period. Our results are clear predictions of QED vacuum polarization effects in the near vicinity of magnetic stars which can be tested with the upcoming X-ray polarimetric observations.