Are fast radio bursts the birthmark of magnetars?

Abstract

A model of fast radio bursts, which enlists young, short period extragalactic magnetars satisfying $B/P > 2 \times 10^{16}$~G~s$^{-1}$ (1~G = 1~statvolt~cm$^{-1}$) as the source, is proposed. When the parallel component $\bE_\parallel$ of the surface electric field (under the scenario of a vacuum magnetosphere) of such pulsars approaches 5 \% of the critical field $E_c = m_e^2 c^3/(e\hbar)$, in strength, the field can readily decay via the Schwinger mechanism into electron-positron pairs, the back reaction of which causes $\bE_\parallel$ to oscillate on a characteristic timescale smaller than the development of a spark gap. Thus, under this scenario, the open field line region of the pulsar magnetosphere is controlled by Schwinger pairs, and their large creation and acceleration rates enable the escaping pairs to coherently emit radio waves directly from the polar cap. The majority of the energy is emitted at frequencies $\lesssim 1$~GHz where the coherent radiation has the highest yield, at a rate large enough to cause the magnetar to lose spin significantly over timescale $\ap$ a few $\times 10^{-3}$~s, the duration of a fast radio burst. Owing to circumstellar environment of a young magnetar, however, the $\lesssim 1$~GHz radiation is likely to be absorbed or reflected by the overlying matter. It is shown that the brightness of the remaining (observable) frequencies of $\ap 1$~GHz and above are on par with a typical fast radio burst. Unless some spin-up mechanism is available to recover the original high rotation rate that triggered the Schwinger mechanism, the fast radio burst will not be repeated again in the same magnetar.