# Magnetic sensitivity in the wing scattering polarization signals of the hydrogen Lyman-alpha line of the solar disk radiation

## TL;DR

This paper demonstrates that the wings of the hydrogen Lyman-alpha line's polarization signals are sensitive to chromospheric magnetic fields, revealing new diagnostic potential for solar atmospheric magnetic field measurements.

## Contribution

It shows that the Lyman-alpha line wings are sensitive to magnetic fields via magneto-optical effects, expanding the diagnostic capabilities of spectropolarimetric observations.

## Key findings

- Wings of Q/I and U/I are sensitive to magnetic fields of 5-100 gauss.
- Magneto-optical effects cause sizable changes in polarization signals.
- Results enhance interpretation of CLASP spectropolarimetric data.

## Abstract

The linear polarization produced by scattering processes in the hydrogen Lyman alpha line of the solar disk radiation is a key observable for probing the chromosphere-corona transition region (TR) and the underlying chromospheric plasma. While the line-center signal encodes information on the magnetic field and three-dimensional structure of the TR, the sizable scattering polarization signals that the joint action of partial frequency redistribution (PRD) and J-state interference produce in the Lyman alpha wings have generally been thought to be sensitive only to the thermal structure of the solar atmosphere. Here we show that the wings of the Q/I and U/I scattering polarization profiles of this line are actually sensitive to the presence of chromospheric magnetic fields, with strengths similar to those that produce the Hanle effect in the line core (i.e., between 5 and 100 gauss, approximately). In spite of the fact that the Zeeman splitting induced by such weak fields is very small compared to the total width of the line, the magneto-optical effects that couple the transfer equations for Stokes Q and U are actually able to produce sizable changes in the Q/I and U/I wings. The theoretical results presented here further expand the diagnostic content of the unprecedented spectropolarimetric observations provided by the Chromospheric Lyman-Alpha Spectropolarimeter (CLASP).