External shock model for the radio afterglows of giant flares from soft γ-ray repeaters

Abstract

Radio afterglows have been detected following two giant flares from soft gamma repeaters (i.e. SGR1900+14, SGR 1806-20). Recent follow-up observations of the December 27 giant flare of SGR 1806-20 have detected a multi-frequency radio afterglow from 240 MHz to 8.46 GHz, extending in time from one week to about one month after the flare. The angular size of the source was also measured for the first time. Here we show that this radio afterglow gives the first piece of clear evidence that an energetic blast wave sweeps up its surrounding medium and produces a synchrotron afterglow, the same mechanism as established for GRB afterglows. © 2006 American Institute of Physics.