# A note on polarized light from Magnetars

## TL;DR

This paper critically examines claims of vacuum birefringence detection in magnetar light, arguing that current data do not conclusively support the phenomenon despite theoretical expectations of polarization effects.

## Contribution

It provides a critical analysis of recent observational claims, clarifying the conditions needed to confirm vacuum birefringence in magnetar emissions.

## Key findings

- Experimental data do not definitively confirm vacuum birefringence.
- Magnetar magnetic fields influence polarization but are not conclusive evidence.
- Theoretical models predict polarization effects that are not yet experimentally verified.

## Abstract

In a recent paper it is claimed that vacuum birefringence has been experimentally observed for the first time by measuring the degree of polarization of visible light from a Magnetar candidate, a neutron star with a magnetic field presumably as large as $B\sim 10^{13}$~G. The role of such a strong magnetic field is twofold. First, the surface of the star emits, at each point, polarized light with linear polarization correlated with the orientation of the magnetic field. Depending on the relative orientation of the magnetic axis of the star with the direction to the distant observer, a certain degree of polarization should be visible. Second, the strong magnetic field in the vacuum surrounding the star could enhance the effective degree of polarization observed: vacuum birefringence. We compare experimental data and theoretical expectations concluding that the conditions to support a claim of strong evidence of vacuum birefringence effects are not met.