# A flaring magnetar in FRB 121102?

## TL;DR

This paper proposes that FRB 121102's persistent radio source and bursts originate from a young magnetar's nebula heated by magnetic flares, with internal shocks producing the observed fast radio bursts.

## Contribution

It introduces a magnetar-based model explaining both the persistent emission and fast radio bursts through nebula heating and shock mechanisms, offering a unified physical scenario.

## Key findings

- The nebula's particle content matches ion ejecta from giant flares.
- Magnetic dissipation heats the nebula, producing efficient radio emission.
- Internal shocks near the magnetar generate millisecond bursts via GHz maser emission.

## Abstract

The persistent radio counterpart of FRB 121102 is estimated to have $N\sim 10^{52}$ particles, energy $E_N\sim 10^{48}$ erg, and size $R\sim 10^{17}$ cm. The source can be a nebula inflated and heated by an intermittent outflow from a magnetar --- a neutron star powered by its magnetic (rather than rotational) energy. The object is young and frequently liberating energy in magnetic flares driven by accelerated ambipolar diffusion in the neutron star core, feeding the nebula and producing bright millisecond bursts. The particle number in the nebula is consistent with ion ejecta from giant flares. The nebula may also contain the freeze-out of electron-positron pairs $N_\pm\sim 10^{51}$ created months after the neutron star birth; the same mechanism offers an explanation for $N_\pm$ in the Crab nebula. The persistent source around FRB 121102 is likely heated by magnetic dissipation and internal waves excited by the magnetar ejecta. The volumetric heating by waves explains the nebula's enormous efficiency in producing radio emission. The repeating radio bursts are suggested to occur much closer to the magnetar, whose flaring magnetosphere drives ultrarelativistic internal shocks into the magnetar wind. The shocks are mediated by Larmor rotation that forms a GHz maser with the observed ms duration. Furthermore, the flare ejecta can become charge-starved and then convert to electromagnetic waves.