The Sources of Fast Radio Bursts

This paper argues that repeating and apparently non-repeating Fast Radio Bursts are distinct classes of events produced by distinct classes of sources. I review the evidence for that division, and then discusses the statistics of these classes. They differ in temporal/spectral space, spectral/duration space and rotation measure; the first two differences indicate different environments. I discuss two of the many models of each class of source: black hole accretion discs for repeating FRB and hypermagnetized neutron stars (some observed to produce SGR) for apparently non-repeating FRB. Appendices suggest low cutoff frequencies of coherent emission that are consistent with these models and with known pulsars, and discuss the necessary conditions for acceleration of energetic particles.