We report the analysis result of UV/X-ray emission from AR Scorpii , which is an intermediate polar ( IP ) composed of a magnetic white dwarf and a M-type star , with the XMM-Newton data .
The X-ray/UV emission clearly shows a large variation over the orbit , and their intensity maximum ( or minimum ) is located at the superior conjunction ( or inferior conjunction ) of the M-type star orbit .
The hardness ratio of the X-ray emission shows a small variation over the orbital phase , and shows no indication of the absorption by an accretion column .
These properties are naturally explained by the emission from the M-type star surface rather than from the accretion column on the WD ’ s star similar to the usual IPs .
Beside , the observed X-ray emission also modulates with WD ’ s spin with a pulse fraction of \sim 14 \% .
The peak position is aligned in the optical/UV/X-ray band .
This supports the hypothesis that the electrons in AR Scorpii are accelerated to a relativistic speed , and emit non-thermal photons via the synchrotron radiation .
In the X-ray bands , the evidence of the power-law spectrum is found in the pulsed component , although the observed emission is dominated by the optically thin thermal plasma emissions with several different temperatures .
It is considered that the magnetic dissipation/reconnection process on the M-type star surface heats up the plasma to a temperature of several keV , and also accelerates the electrons to the relativistic speed .
The relativistic electrons are trapped in the WD ’ s closed magnetic field lines by the magnetic mirror effect .
In this model , the observed pulsed component is explained by the emissions from the first magnetic mirror point .