The impulsive phase of magnetar giant flares: assessing linear tearing as the trigger mechanism

Publication Type
Journal Article
Year of Publication
Elenbaas, C.
Watts, A. L.
Turolla, R.
Heyl,J. S
Name of Publication
Monthly Notices of the Royal Astronomical Society
Date Published
March 1, 2016
ISBN Number
magnetic reconnection; stars: magnetars; X-rays: bursts

Giant γ-ray flares comprise the most extreme radiation eventsobserved from magnetars. Developing on (sub)millisecond time-scales andgenerating vast amounts of energy within a fraction of a second, theinitial phase of these extraordinary bursts presents a significantchallenge for candidate trigger mechanisms. Here we assess andcritically analyse the linear growth of the relativistic tearinginstability in a globally twisted magnetosphere as the trigger mechanismfor giant γ-ray flares. Our main constraints are given by theobserved emission time-scales, the energy output of the giant flarespike, and inferred dipolar magnetic field strengths. We find that theminimum growth time of the linear mode is comparable to the e-foldingrise time, i.e. ˜10-1 ms. With this result, weconstrain basic geometric parameters of the current sheet. We alsodiscuss the validity of the presumption that the e-folding emissiontime-scale may be equated with the growth time of a magnetohydrodynamicinstability.