  We use the observed properties of fast radio bursts (FRBs) and a number of
general physical considerations to provide a broad-brush model for the physical
properties of FRB sources and the radiation mechanism. We show that the
magnetic field in the source region should be at least 10^{14} Gauss. This
strong field is required to ensure that the electrons have sufficiently high
ground state Landau energy so that particle collisions, instabilities, and
strong electric and magnetic fields associated with the FRB radiation do not
perturb electrons' motion in the direction transverse to the magnetic field and
destroy their coherent motion; coherence is required by the high observed
brightness temperature of FRB radiation. The electric field in the source
region required to sustain particle motion for a wave period is estimated to be
of order 10^{11} esu. These requirements suggest that FRBs are produced near
the surface of magnetars perhaps via forced reconnection of magnetic fields to
produce episodic, repeated, outbursts. The beaming-corrected energy release in
these bursts is estimated to be ~10^{36} ergs, whereas the total energy in the
magnetic field is at least ~10^{45} ergs. We provide a number of predictions
for this model which can be tested by future observations. One of which is that
short duration FRB-like bursts should exist at much higher frequencies,
possibly up to optical.
