Model of extended emission of short Gamma-ray Bursts
  Until now the existence of extended emission is an intriguing property of short bursts. It is not clear what is the nature of the extended emission. It might be a rising x-ray afterglow, or it could be a manifestation of the prolonged activity of a central engine. We consider short duration gamma-ray bursts, emphasizing the common properties of short bursts and short burst with extended emission. Assuming that the extended emission with broad dynamic range is a common property of short bursts, we propose a two jet model which can describe both short main episode of hard spectra emission, specific for short bursts, and softer spectra extended emission by different off axis position of observer. The toy model involves a short duration jet powered by heating due to $\nu\tilde{\nu}$ annihilation and long-lived Blandford-Znajek jet with significantly narrow opening angle. Our proposed model is a plausible mechanism for short duration burst energization, and can explain both short burst with and without extended emission within a single class of progenitor. 
Maxim V. Barkov, Alexei S. Pozanenko
astro-ph.HE