Rapid Evolution of the White Dwarf Pulsar AR Scorpii

Abstract

Abstract Analysis of AR Sco optical light curves spanning 9 yr shows a secular change in the relative amplitudes of the beat pulse pairs generated by the two magnetic poles of its rotating white dwarf. Recent photometry now shows that the primary and secondary beat pulses have similar amplitudes, while in 2015 the primary pulse was approximately twice that of the secondary peak. The equalization in the beat pulse amplitudes is also seen in the linearly polarized flux. This rapid evolution is consistent with precession of the white dwarf spin axis. The observations imply that the pulse amplitudes cycle over a period of ≳40 yr but that the upper limit is currently poorly constrained. If precession is the mechanism driving the evolution, then over the next 10 yr the ratio of the beat pulse amplitudes will reach a maximum followed by a return to asymmetric beat pulses.