Comment on "Intense Superradiant X Rays from a Compact Source Using a Nanocathode Array and Emittance Exchange".

The authors discuss aspects of the study on x-rays production from a compact source using nanocathode field-emission array. They say that there was an error on the number of photon radiation made by the modulated electron beam. They state that beam radiation was due to the inverse Compton scattering and can be resolved as undulator radiation. They add that the error was through the wrong estimate of the emission angle.