  Axions generated thermally in the solar core can convert nearly directly to
X-rays as they pass through the solar atmosphere via interaction with the
magnetic field. The result of this conversion process would be a diffuse
centrally-concentrated source of few-keV X-rays at disk center; it would have a
known dimension, of order 10% of the solar diameter, and a spectral
distribution resembling the blackbody spectrum of the solar core. Its spatial
structure in detail would depend on the distribution of mass and field in the
solar atmosphere. The brightness of the source depends upon these factors as
well as the unknown coupling constant and the unknown mass of the axion; this
particle is hypothetical and no firm evidence for its existence has been found
yet. We describe the solar magnetic environment as an axion/photon converter
and discuss the upper limits obtained by existing and dedicated observations
from three solar X-ray observatories: Yohkoh, RHESSI, and Hinode
