AR Sco: A Precessing White Dwarf Synchronar?

• Published in: The Astrophysical journal Vol. 835; no. 2; pp. 150 - 153
• Main Author: Katz, J. I.
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.02.2017; IOP Publishing
• Subjects: Accretion; Astrophysics; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; binaries: close; Bow waves; Deposition; EMISSION; Magnetars; MAGNETIC FIELDS; MAGNETIC MOMENTS; MAGNETIC RECONNECTION; NEUTRON STARS; Polars (astronomy); Radiation; Red dwarf stars; ROTATION; stars: individual (AR Sco); stars: magnetic field; stars: peculiar; stars: variables: general; stars: white dwarfs; STELLAR ATMOSPHERES; Synchronism; SYNCHRONIZATION; SYNCHROTRON RADIATION; WHITE DWARF STARS
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/835/2/150

The emission of the white dwarf-M dwarf binary AR Sco is driven by the rapid synchronization of its white dwarf, rather than by accretion. Synchronization requires a magnetic field ∼100 Gauss at the M dwarf and Gauss at the white dwarf, larger than the fields of most intermediate polars but within the range of fields of known magnetic white dwarfs. The spindown power is dissipated in the atmosphere of the M dwarf, within the near zone of the rotating white dwarf's field, by magnetic reconnection, accelerating particles that produce the observed synchrotron radiation. The displacement of the optical maximum from conjunction may be explained either by dissipation in a bow wave as the white dwarf's magnetic field sweeps past the M dwarf or by a misaligned white dwarf rotation axis and oblique magnetic moment. In the latter case the rotation axis precesses with a period of decades, predicting a drift in the orbital phase of the optical maximum. Binaries whose emission is powered by synchronization may be termed synchronars, in analogy to magnetars.