Hadronic model for the non-thermal radiation from the binary system AR~Scorpii

AR Scorpii is a close binary system containing a rotation powered white dwarf and a low mass M type companion star. This system shows non-thermal emission extending up to the X-ray energy range. We consider hybrid (lepto-hadronic) and pure hadronic models for the high energy non-thermal processes in this binary system. Relativistic electrons and hadrons are assumed to be accelerated in a strongly magnetised, turbulent region formed in collision of a rotating white dwarf magnetosphere and a magnetosphere/dense atmosphere of the M dwarf star. We propose that the non-thermal X-ray emission is produced either by the primary electrons or the secondary $e^\pm$ pairs from decay of charged pions created in collisions of hadrons with the companion star atmosphere. We show that the accompanying $\gamma$-ray emission from decay of neutral pions, that are produced by these same protons, is expected to be on the detectability level of the present and/or the future satellite and Cherenkov telescopes. The $\gamma$-ray observations of the binary system AR Sco should allow to constrain the efficiency of hadron and electron acceleration and also the details of the radiation processes.
Comment: 11 pages. 2 figures, accepted to MNRAS Let