Axion-Like Particles, Magnetars, and X-ray Astronomy
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uncovered an interesting factorization property. Using reasonable assumptions, we
then computed the ALP-to-photon conversion probability analytically. Therefore,
the Stokes parameters in the presence of ALPs were completely determined by the
parameters of the theory, i.e. in terms of the astrophysics of magnetars and in terms
of the ALP parameters. It is then straightforward to use these results to constrain the
ALP parameter space for specific magnetars [5, 6]. Such an analysis shows that the
Stokes parameter Q is modified by the presence of ALP oscillations and can even
change sign, leading to a clear effect on X-ray polarization.
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