  Theoretical and experimental study of fast electron beams attracts a lot of
attention in the astrophysics and laboratory. In the case of solar flares the
problem of reliable beam detection and diagnostics is of exceptional
importance. This paper explores the fact that the electron beams moving oblique
to the magnetic field or along the field with some angular scatter around the
beam propagation direction can generate microwave continuum bursts via
gyrosynchrotron mechanism. The characteristics of the microwave bursts produced
by beams differ from those in case of isotropic or loss-cone distributions,
which suggests a new tool for quantitative diagnostics of the beams in the
solar corona. To demonstrate the potentiality of this tool, we analyze here a
radio burst occurred during an impulsive flare 1B/M6.7 on 10 March 2001 (AR
9368, N27W42). Based on detailed analysis of the spectral, temporal, and
spatial relationships, we obtained firm evidence that the microwave continuum
burst is produced by electron beams. For the first time we developed and
applied a new forward fitting algorithm based on exact gyrosynchrotron formulae
and employing both the total power and polarization measurements to solve the
inverse problem of the beam diagnostics. We found that the burst is generated
by a oblique beam in a region of reasonably strong magnetic field ($\sim
200-300$ G) and the burst is observed at a quasi-transverse viewing angle. We
found that the life time of the emitting electrons in the radio source is
relatively short, $\tau_l \approx 0.5$ s, consistent with a single reflection
of the electrons from a magnetic mirror at the foot point with the stronger
magnetic field. We discuss the implications of these findings for the electron
acceleration in flares and for beam diagnostics.
