VLA Observations of the AE Aqr-type Cataclysmic Variable LAMOST J024048.51+195226.9

TL;DR

This study reports VLA radio observations of the cataclysmic variable J0240+19, revealing persistent, polarized radio emission distinct from AE Aqr, likely originating from the donor star's corona rather than the white dwarf's magnetosphere.

Contribution

First detailed radio characterization of J0240+19 showing its emission differs from AE Aqr, suggesting a different emission mechanism involving the donor star's corona.

Findings

J0240+19 exhibits high circular polarization and negative spectral index.

Radio emission likely from the donor star's corona, not the white dwarf's magnetosphere.

J0240+19 is a persistent, weak radio source suitable for studying CV radio emissions.

Abstract

AE Aqr was until recently the only known magnetic cataclysmic variable (MCV) containing a rapidly spinning (33.08 s) white dwarf (WD). Its radio emission is believed to be a superposition of synchrotron emitting plasmoids, because it has a positive spectral index spanning three orders of magnitude (~2-2000 GHz) and is unpolarized. Both characteristics are unusual for MCVs. Recently, Thorstensen has suggested that the cataclysmic variable LAMOST J024048.51+195226.9 (henceforth, J0240+19) is a twin of AE Aqr based on its optical spectra. Optical photometry shows the star to be a high-inclination, eclipsing binary with a spin period of 24.93 s, making it the fastest spinning WD. This paper presents three hours of Very Large Array radio observations of J0240+19. These observations show that the persistent radio emission from J0240+19 is dissimilar to that of AE Aqr in that it shows high circular polarization and a negative spectral index. The emission is most similar to the nova-like CV V603 Aql. We argue that the radio emission is caused by a superposition of plasmoids emitting plasma radiation or electron cyclotron maser emission from the lower corona of the donor star and not from the magnetosphere near the WD, because the latter site is expected to be modulated at the orbital period of the binary and to show eclipses of which there is no evidence. The radio source J0240+19, although weak (<1 mJy), is a persistent source in a high-inclination eclipsing binary, making it a good laboratory for studying radio emission from CVs.