The Sources of Fast Radio Bursts

There are two distinct classes of Fast Radio Bursts: repeaters and apparent non-repeaters, differing in spectro-temporal properties and duty factors. There are strict limits on periodicities of repeaters, arguing against models based on neutron stars and in favor of black hole accretion discs; long-period modulation of activity is consistent with disc precession. Apparent non-repeaters must repeat because catastrophic events are too rare to explain them. The Galactic FRB 200428, identified with a Soft Gamma Repeater, would be an apparent non-repeater if more distant, and its greatest burst was an outlier like the greatest SGR outbursts, suggesting an identification.

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