http://arxiv.org/abs/1403.2436
Recent calculations of the 3-D scattering of X-rays produced by the conversion of solar axions suggest that the sunward magnetosphere could be a source of 0.2-10keV photons, observable without violating the Sun-/Earth-avoidance constraints of operational telescopes. Observed from High Earth Orbit, this conversion X-ray intensity may be seasonally modulated due to the changing visibility of the sunward magnetic field region. A simple model of the geomagnetic field is combined with the full ephemeris of XMM to predict the seasonal variation of the conversion X-ray intensity and its north-south asymmetry relative to the ecliptic. This model is compared with stacked XMM EPIC pn, MOS1 and MOS2 blank sky datasets from which point sources have been systematically removed and which have been rigorously screened against 1-500keV soft protons. Remarkably, when the residual flux is segregated according to spacecraft season, a very significant (>3sigma), 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. We conclude that this variable signal is consistent with the conversion of solar axions in the Earth’s magnetic field. Its variation with energy is consistent with a solar axion production spectrum dominated by bremsstrahlung- and Compton-like processes, distinct from a Primakoff thermal spectrum. That is, axion-electron coupling dominates over axion-photon coupling and the peak of the axion energy spectrum is below 1keV. A value of 1.5E-11 GeV-1 is derived for the geometric mean of the axion-photon and axion-electron coupling constants, for an axion mass in the micro-eV range. Preliminary results are given of a search for axion-conversion X-ray lines, in particular the 14.4keV M1 57Fe transition line and the recently predicted narrow features due to Si and S in the solar core.
G. Fraser, A. Read, S. Sembay, et. al.
Wed, 12 Mar 14
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