  We present lightcurves obtained in X-ray by the XMM-Newton EPIC cameras and
simultaneous radio lightcurves obtained with the VLA for five active M-type
flare stars. A number of flare events were observed, and by comparing radio
with X-ray data, we consider various possible flare mechanisms. In cases where
there seems to be a clear correlation between radio and X-ray activity, we use
an energy budget argument to show that the heating which leads to the X-ray
emission could be due to the same particles emitting in the radio. In cases
where there is radio activity without corresponding X-ray activity, we argue
that the radio emission is likely to arise from coherent processes involving
comparatively few particles. In one case, we are able to show from polarization
of the radio emission that this is almost certainly the case. Cases for which
X-ray activity is seen without corresponding radio activity are more difficult
to explain. We suggest that the heating particles may be accelerated to very
high energy, and the resulting synchrotron radio emission may be beamed in
directions other than the line of sight.
