The Sources of Apparently Non-Repeating FRB

Abstract

There are insufficient catastrophic events (collapse, explosion or merger of stars or compact objects) to explain the cosmologically local rate of apparently non-repeating FRB if each such catastrophic event produces a single FRB. Unless produced by some novel and unsuspected but comparatively frequent event, apparently non-repeating FRB must actually repeat many times in the lifetimes of their sources. Yet no such infrequent repetitions (in contrast to the frequent activity of FRB known to repeat) have been observed, constraining their repetition rates and active lifetimes. The absence of more frequent weaker but detectable repetitive outbursts in apparent non-repeaters resembles the distribution of SGR outbursts, with a large gap between giant outbursts and lesser outbursts. This suggests mini-SGR as sources, more energetic than SGR 1935$+$2154 associated with FRB 200428 but less energetic than SGR 1806$-$20 that had no associated FRB. Their largest radio outbursts would, at cosmological distances, be apparently non-repeating FRB and their X-ray and gamma-ray outbursts would be undetectable. The large gap between the strongest outburst of FRB 200428 and its lesser outbursts resembles the gamma-ray properties of individual well-observed SGR; at twenty times its actual distance, FRB 200428 would have been an apparent non-repeater.