Magnetars in Binaries as the Engine of Actively Repeating Fast Radio Bursts

TL;DR

This paper proposes a unified model where most active repeating fast radio bursts originate from magnetars in binary systems with aligned axes, explaining diverse observational features and the rarity of active repeaters.

Contribution

It introduces a novel binary magnetar framework that accounts for various FRB behaviors and predicts a small fraction of magnetars in binaries with specific alignments.

Findings

A few percent of magnetars are in binary systems.

Binary systems with aligned axes can produce diverse FRB phenomena.

The companion may trigger or sustain FRB activity.

Abstract

The association between FRB 20200428D and the Galactic magnetar SGR J1935+2154 makes magnetars the leading engine of cosmological fast radio bursts (FRBs). However, there is a list of puzzles for this magnetar-for-all-FRBs scenario: known Galactic magnetars are all isolated and none of them are active repeaters; some cosmological repeaters have extremely high repetition rates but without any measurable spin-related periodicity; some show long-term periodic active windows; and some show diverse rotation measure (RM) evolution patterns, such as quasi-periodic fluctuations, sign reversals, and abrupt RM flares. Here we propose a unified theoretical framework for FRBs within the framework of magnetar engine: Most active repeating FRBs originate from magnetars in binary systems with nearly aligned rotation and magnetic axes, some of which with a triple-aligned geometry, i.e. with an alignment with the orbital axis as well; whereas apparent non-repeaters and inactive repeaters originate from magnetars in isolated systems or in binaries with a misaligned geometry. By studying various magnetar formation channels using population syntheses, we show that a few percent of magnetars in the universe can be in binary systems, most with a massive star companion and some with aligned geometry. We suggest that such binary systems can account for the rich phenomenology of active repeaters. We suggest that the existence of a companion helps to maintain the aligned geometry and that the companion may play an active role in triggering FRBs in an active repeater source.