Origin of sources of repeating fast radio bursts with periodicity in close binary systems

It is proposed that sources of repeating fast radio bursts with detected periodicity are magnetars with extremely short initial spin periods at the protoneutron star stage, formed in binaries after tidal synchronization of their progenitor cores on late stages of thermonuclear burning in very close systems with orbital periods about a few days. This formation channel is in several respects different from evolution of progenitors of normal magnetars, and thus, it explains some differences between repeating and non-repeating sources of FRBs.