Solar X-rays from Axions: Rest-Mass Dependent Signatures

TL;DR

This paper proposes that solar X-ray spectra can be explained by axion-photon conversion occurring deep in the Sun's photosphere, with spectral features depending on axion mass, supported by observational data from quiet Sun periods.

Contribution

It introduces a novel explanation for solar X-ray spectral shapes based on axion regeneration, linking spectral features to axion mass and providing observational support from quiet Sun data.

Findings

Spectral shape of solar X-rays follows a power law with activity-dependent steepness.

Axion mass around 17 meV/c2 can reproduce observed spectral features.

Quiet Sun X-ray spectra align with the axion scenario.

Abstract

The spectral shape of solar X-rays is a power law. The more active the Sun is, the less steep the distribution. This behaviour can be explained by axion regeneration to X-rays occurring ~400km deep into the photosphere. Their down-comptonization reproduces the measured spectral shape, pointing at axions with rest mass m_a~17 meV/c2, without contradicting astrophysical-laboratory limits. Directly measured soft X-ray spectra from the extremely quiet Sun during 2009 (SphinX mission), though hitherto overlooked, fitt the axion scenario.