Waiting for the big one: A new class of soft gamma-ray repeater outbursts?

It is suggested that magnetars eventually become unstable to a dynamic overturning instability that destroys most of their dipole moment in a single event. It is further suggested that such an instability would produce a supergiant version of the largest soft gamma-ray bursts that have thus far been observed, and that they could be observed out to tens or even 10² Mpc. Persistent emission and afterglows from the fireball might confirm positive identification with nearby galaxies and perhaps provide other distinguishing features as well.