  Before 1985, attempts to detect radio or X-ray emission from Magnetic CP
(MCP) stars were either fruitless or ambiguous. However, more successful
results have been obtained in the last dozen years: (i) Radio emission has now
been detected from ~35 MCP stars of the Helium-peculiar and Silicon-strong
subclasses, with a functional dependence of radio luminosity L_{R} \propto
T_eff^7 H_s^{1.2} P_rot^{-0.6}, where T_eff is the effective temperature, H_s
is the surface magnetic field strength, and P_rot is the rotational period;
rotational modulation of the radio emission has also been observed for several
MCP stars. All of this evidence suggests that it is the MCP stars themselves,
not close companions, that are responsible for the radio emission; (ii) The
X-ray emission properties of MCP stars are however still poorly characterized:
although a moderate number (~18) have by now been associated with X-ray
sources, the lack of a clear correlation of this X-ray emission with other
stellar parameters has made it difficult to rule out the close companion
hypothesis.
