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The soft X-ray flux produced by solar axions in the Earth's magnetic field isevaluated in the context of ESA's XMM-Newton observatory. Recent calculationsof the scattering of axion-conversion X-rays suggest that the sunwardmagnetosphere could be an observable source of 0.2-10 keV photons. ForXMM-Newton, any conversion X-ray intensity will be seasonally modulated byvirtue of the changing visibility of the sunward magnetic field region. Asimple model of the geomagnetic field is combined with the ephemeris ofXMM-Newton to predict the seasonal variation of the conversion X-ray intensity.This model is compared with stacked XMM-Newton blank sky datasets from whichpoint sources have been systematically removed. Remarkably, a seasonallyvarying X-ray background signal is observed. The EPIC count rates are in theratio of their X-ray grasps, indicating a non-instrumental, external photonorigin, with significances of 11(pn), 4(MOS1) and 5(MOS2) sigma. Afterexamining the constituent observations spatially, temporally and in terms ofthe cosmic X-ray background, we conclude that this variable signal isconsistent with the conversion of solar axions in the Earth's magnetic field.The spectrum is consistent with a solar axion spectrum dominated bybremsstrahlung- and Compton-like processes, i.e. axion-electron couplingdominates over axion-photon coupling and the peak of the axion spectrum isbelow 1 keV. A value of 2.2e-22 /GeV is derived for the product of theaxion-photon and axion-electron coupling constants, for an axion mass in themicro-eV range. Comparisons with limits derived from white dwarf cooling maynot be applicable, as these refer to axions in the 0.01 eV range. Preliminaryresults are given of a search for axion-conversion X-ray lines, in particularthe predicted features due to silicon, sulphur and iron in the solar core, andthe 14.4 keV transition line from 57Fe.

Potential solar axion signatures in X-ray observations with the XMM-Newton observatory