Orbital and Precession Periods in Repeating FRB 20121102A

TL;DR

This paper proposes that the observed 4.605-day period in FRB 20121102A is due to an orbiting star around a black hole, and the 157-day period is caused by accretion disc precession, offering a new interpretation of the system's dynamics.

Contribution

It introduces a novel model linking the observed periodicities to orbital motion and disc precession in a black hole system, suggesting an evolved mass-losing star.

Findings

The 4.605-day period is likely the orbital period of a star around a black hole.

The 157-day period is interpreted as the precession period of the accretion disc.

The star involved is probably an evolved, mass-losing star.

Abstract

Li {\it et al.\/} (2024) reported a 4.605 day period in the repeating FRB 20121102A in addition to the previously reported 157 day modulation of its activity. This note suggests that the shorter period is the orbital period of a mass-transferring star orbiting a black hole, possibly of intermediate mass, and that the 157 day period is the precession period of an accretion disc around the black hole. The mass-losing star must be evolved.