An X-Ray Study of the White Dwarf Binary AR Scorpii

J. Takata, X. F. Wang, H. H. Wang, L. C.C. Lin, C. P. Hu, K. L. Li, A. K.H. Kong

Research output: Contribution to journalArticlepeer-review

Abstract

We report a study of X-ray emission from the white dwarf/M-type star binary system AR Scorpii using archival data taken in 2016-2020. It has been known that the X-ray emission is dominated by optically thin thermal plasma emission and its flux level varies significantly over the orbital phase. The X-ray emission also contains a component that modulates with the beat frequency between the white dwarf's spin frequency and orbital frequency. In this new analysis, the 2020 data taken by NICER shows that the X-ray emission modulates with the spin frequency as well as with the beat frequency, indicating that part of the X-ray emission comes from the white dwarf's magnetosphere. It is found that the signal of the spin frequency appears only at a specific orbital phase, while the beat signal appears over the orbital phase. We interpret the X-ray emission modulating with the spin frequency and the beat frequency as a result of synchrotron emission from electrons with smaller and larger pitch angles, respectively. In the long-term evolution, the beat pulse profile averaged over the orbital phase changes from a single-peak structure in 2016/2018 to a double-peak structure in 2020. The observed X-ray flux levels measured in 2016/2017 are higher than those measured in 2018/2020. The plasma temperature and the amplitude of the orbital waveform might vary with time too. These results indicate that the X-ray emission from AR Scorpii evolves on a timescale of years. This long-term evolution would be explained by a superorbital modulation related to, for example, a precession of the white dwarf or a fluctuation of the system related to the activity of the companion star.

Original languageEnglish
Article number115
JournalAstrophysical Journal
Volume907
Issue number2
DOIs
Publication statusPublished - 2021 Feb 1

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Fingerprint Dive into the research topics of 'An X-Ray Study of the White Dwarf Binary AR Scorpii'. Together they form a unique fingerprint.

Cite this