  Bursts of millisecond duration were recently discovered in the 1 GHz band.
There is a strong evidence that they come from $\sim 1 $ Gpc distances, which
implies extraordinary high brightness temperature. I propose that these bursts
could be attributed to synchrotron maser emission from relativistic, magnetized
shocks. At the onset of the magnetar flare, a strongly magnetized pulse is
formed, which propagates away through the relativistic magnetar wind and
eventually reaches the nebula inflated by the wind within the surrounding
medium. I show that the observed radio bursts could be generated at shocks
formed via the interaction of the magnetic pulse with the plasma within the
nebula. The model predicts strong millisecond bursts in the TeV band, which
could be observed even from distant galaxies.
