Superflares from magnetars revealing the GRB central engine

Abstract

Long-duration gamma-ray bursts (GRBs) may be powered by the rotational energy of a millisecond magnetar. I argue that the GRB-driving magnetars lie at the high end of the distribution of magnetic field strengths of magnetars. The field of GRB magnetars decays on time-scale of hundreds of years and can power soft gamma-ray repeater (SGR)-like flares up to ~ 100 times more powerful than the 2004 event of SGR 1806-20. A few of these flares per year may have been observed by the Burst and Transient Source Experiment (BATSE) and classified as short-duration GRBs. Association of one of these superflares with a nearby dL ≲ 250 Mpc galaxy and the discovery of a, coincident in space, 100-yr-old GRB afterglow (observed in the radio) will be the characteristic signature of the magnetar model for GRBs. © 2010 The Authors. Journal compilation © 2010 RAS.