Hyperflares of SGRs as an engine for millisecond extragalactic radio bursts

Abstract

We propose that the strong millisecond extragalactic radio burst (mERB) discovered by Lorimer et al. (2007) may be related to a hyperflare from an extragalactic soft gamma-ray repeater. The expected rate of such hyperflares, $\sim$ 20 - 100 d$^{-1}$ Gpc$^{-3}$, is in good correspondence with the value estimated by Lorimer et al. The possible mechanism of radio emission can be related to the tearing mode instability in the magnetar magnetosphere as discussed by Lyutikov (2002), and can produce the radio flux corresponding to the observed $\sim$ 30 Jy from the mERB using a simple scaling of the burst energy.