Radio observations of the magnetic chemically peculiar star CU Vir, carried
out with the VLA in three different days, show that the radio emission at 20 cm
is characterized by a strong enhancement at particular rotational phases. This
radio emission is found to be right hand polarized with a degree of
polarization close to 100 %. As common for this class of stars, the magnetic
axis of CU Vir is oblique with respect to the rotational axis. By comparing the
20 cm radio light curve with the effective magnetic field available from the
literature, a coincidence of the main peaks of the radio emission with the
magnetic nulls has been found. This happens when the magnetic axis lies in the
plane of the sky. We suggest that the high degree of polarization, together
with the high directivity of the radiation, can be explained in terms of
coherent radio emission. The data have been interpreted on the basis of the
Electron Cyclotron Maser Emission from electrons accelerated in current sheets
out of the Alfven radius toward the stellar surface and eventually reflected
outward by magnetic mirroring.Comment: 9 pages, 12 figures. To be published in A&