Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Potential solar axion signatures in X-ray observations with the
  XMM-Newton observatory   The soft X-ray flux produced by solar axions in the Earth's magnetic field is
evaluated in the context of ESA's XMM-Newton observatory. Recent calculations
of the scattering of axion-conversion X-rays suggest that the sunward
magnetosphere could be an observable source of 0.2-10 keV photons. For
XMM-Newton, any conversion X-ray intensity will be seasonally modulated by
virtue of the changing visibility of the sunward magnetic field region. A
simple model of the geomagnetic field is combined with the ephemeris of
XMM-Newton to predict the seasonal variation of the conversion X-ray intensity.
This model is compared with stacked XMM-Newton blank sky datasets from which
point sources have been systematically removed. Remarkably, a seasonally
varying X-ray background signal is observed. The EPIC count rates are in the
ratio of their X-ray grasps, indicating a non-instrumental, external photon
origin, with significances of 11(pn), 4(MOS1) and 5(MOS2) sigma. After
examining the constituent observations spatially, temporally and in terms of
the cosmic X-ray background, we conclude that this variable signal is
consistent with the conversion of solar axions in the Earth's magnetic field.
The spectrum is consistent with a solar axion spectrum dominated by
bremsstrahlung- and Compton-like processes, i.e. axion-electron coupling
dominates over axion-photon coupling and the peak of the axion spectrum is
below 1 keV. A value of 2.2e-22 /GeV is derived for the product of the
axion-photon and axion-electron coupling constants, for an axion mass in the
micro-eV range. Comparisons with limits derived from white dwarf cooling may
not be applicable, as these refer to axions in the 0.01 eV range. Preliminary
results are given of a search for axion-conversion X-ray lines, in particular
the predicted features due to silicon, sulphur and iron in the solar core, and
the 14.4 keV transition line from 57Fe.

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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
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The categories of this paper are: q-fin
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The categories of this paper are: nlin
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The categories of this paper are: acc-phys
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The categories of this paper are: eess
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The categories of this paper are: cond-mat
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The categories of this paper are: q-bio
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The categories of this paper are: comp-gas
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The categories of this paper are: math-ph
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The categories of this paper are: math
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The categories of this paper are: econ
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The categories of this paper are: chem-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: solv-int
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The categories of this paper are: bayes-an