Observational analysis shows significant polarization in a white dwarf, indicating the X-ray scattering surface aligns with the accretion column height.
We present the first first X-ray polarization measurements of a white dwarf (WD), the intermediate polar EX Hya. We measured significant polarization only in the 2–3 keV energy band with a polarization degree of 8% at a 3 σ significance. No significant polarization was detected above 3 keV, which we attribute to the higher energy bands having lower signal to noise. We found that the scattering surface detected by the Imaging X-ray Polarimetry Explorer appears to be nearly perpendicular to the optical scattering plane, showing that the X-ray scattering surface is the WD and close to the base of the accretion column. Finally, we show how the polarization can be used to estimate the height of the accretion shock above the WD’s surface.
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Gunderson et al. (2025) studied this question.
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