Particles going faster than light in vacuum do not exist. Overcoming speed of light means a violation of causality (even if possible formulations of relativity in this case exist and the corresponding field theories describe the so called tachyonic excitations, but these imply a vacuum instability and then they are never observed in nature).
Cerenkov radiation appears when a particle moves faster than the speed of light in the given medium (not vacuum). In a medium the speed of light is given by v=c/n being n the refraction index of the medium itself and so v is smaller than c. A particle can travel faster than v in the medium producing electromagnetic radiation much in the same way of the sonic bang of an aircraft moving faster than the sound speed in air.
Jon