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.Comment: To appear in Proceedings of the 5th Patras Axion Workshop, Durham
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