Active region filaments might harbor weak magnetic fields

TL;DR

This paper proposes a two-component model to explain Zeeman-only spectropolarimetric observations of active region filaments, suggesting that mixed magnetic field components can cancel Hanle signatures, affecting interpretation of magnetic field measurements.

Contribution

It introduces a novel two-component model with horizontal magnetic fields to explain Zeeman-only signatures in active region filaments, accounting for the absence of Hanle effect signals.

Findings

The model explains Zeeman-only profiles by opposing polarization signatures from different components.

The lower component has strong magnetic fields (~600 G), while the upper has weak fields (~10 G).

The combined effect can cancel Hanle signatures, influencing magnetic field diagnostics.

Abstract

Recent spectropolarimetric observations of active region filaments have revealed polarization profiles with signatures typical of the strong field Zeeman regime. The conspicuous absence in those observations of scattering polarization and Hanle effect signatures was then pointed out by some authors. This was interpreted either as a signature of mixed "turbulent" field components or as a result of optical thickness. In this article, we present a natural scenario to explain these Zeeman-only spectro-polarimetric observations of active region filaments. We propose a two-component model, one on top of the other. Both components have horizontal fields, the azimuth difference between them being close to 90 degrees. The component that lies lower in the atmosphere is permeated by a strong field of the order of 600 G, while the upper component has much weaker fields, of the order of 10 G. The ensuing scattering polarization signatures of the individual components have opposite signs, so that its combination along the line of sight reduces --and even can cancel out-- the Hanle signatures, giving rise to an apparent only-Zeeman profile. This model is also applicable to other chromospheric structures seen in absorption above active regions.