  Extensive radio data of two Algol systems and two RS CVn binaries were
re-analyzed. We found evidence for a new periodicity that we interpret as a
superhump in Algol, in which it may have been expected according to its
semi-detached nature and low binary mass ratio. This is the first detection of
the superhump phenomenon in the radio and the first observation of superhumps
in Algol systems. According to our result, the accretion disk in Algol
precesses in spite of its non-Keplerian nature and therefore this phenomenon is
not restricted to the classical Keplerian disks in compact binaries.We propose
that in Algol systems with short orbital periods, the disk is magnetically
active as well as the secondary star. The magnetic field in the disk originates
from amplification of the seed field in the magnetized material transferred
from the secondary. The disk and stellar fields interact with each other, with
reconnection of the field lines causing flares and particle acceleration.
Relativistic particles are trapped in the field and directed toward the polar
regions of the secondary star because of the dipole structure of its magnetic
field. Our proposed model for the magnetic activity in Algol systems provides a
simple explanation to the observed properties of Algol in the radio
wavelengths, and to the presence of quiescent gyrosynchrotron emission near the
polar region of the secondary star, where electrons are difficult to be
confined if the field lines are open as in normal single magnetic stars. We
propose that the superhump variation in the radio is generated by enhanced
reconnection when the elongated side of the elliptic disk is the closest to the
cool star. This leads to flares and enhancement in particle acceleration and is
manifested as stronger gyrosynchrotron radiation.
