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Abstract: We examine two trigger mechanisms, one internal and the other external to theneutron star, that give rise to the intense soft gamma-ray repeater SGR giantflares. So far, three giant flares have been observed from the three out of theseven confirmed SGRs on March 5, 1979, August 27, 1998, and December 27, 2004.The last two events were found to be much more powerful than the first, andboth showcased the existence of a precursor, that we show to have had initiatedthe main flare. In the internal mechanism, we propose that the strongly woundup poloidal magnetic field develops tangential discontinuities and dissipatesits torsional energy in heating the crust. The timescale for the instability todevelop coincides with the duration of the quiescent state that followed theprecursor. Alternatively, we develop a reconnection model based on thehypothesis that shearing motion of the footpoints causes the materialization ofa Sweet-Parker current layer in the magnetosphere. The thinning of thismacroscopic layer due to the development of an embedded super-hot turbulentcurrent layer switches on the impulsive Hall reconnection, which powers thegiant flare. Again, we show that the thinning time is on the order of thepreflare quiescent time. This model naturally explains the origin of theobserved nonthermal radiation during the flares, as well as the post flareradio afterglows.

Author: Ramandeep Gill, Jeremy S. Heyl

Source: https://arxiv.org/

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