Solar-type Theoretical Model for Magnetar Giant Flare

In the framework of solar flare/coronal mass ejection theory, we propose a theoretical model for magnetar giant flare, which can explain the flaring activity on 2004 December 27 from SGR1806-20 comprehensively. As is the case with solar flare, explosive magnetic reconnection in magnetosphere takes a major role in the energetics of magnetar flare. However, cooling and energy transport processes in magnetar flare differ from those in solar flare essentially. In the magnetar flare, radiative cooling determines the flare temperature. Furthermore, released magnetic energy is transported by photon flux unlike electron heat conduction in solar flare. Then incident heat flux drives the baryonic mass evaporation from the crustal surface of magnetar. We find that the temperature and evaporating baryonic mass in flaring activity of magnetar are described by simple scaling relations. Applying the magnetic reconnection model to the giant flare on 2004 from SGR1806-20, the difference of the released energy between preflare and main burst phases is explained by the volume difference of the active region. In addition, our model predicts that the evaporating bayonic matter in the preflare phase is the origin of the expanding ejecta observed in assocication with the giant flare from SGR1806-20. Subject headings: stars:individual: SGR 1806-20 — stars:magnetic fields — stars:neutron