July 27, 2015 to August 21, 2015
Nordita, Stockholm
Europe/Stockholm timezone

Magnetar giant flare timescales & the relativistic tearing mode

Not scheduled
132:028 (Nordita, Stockholm)

132:028

Nordita, Stockholm

Poster Workshop, August 10-14

Speaker

Mr Chris Elenbaas (University of Amsterdam)

Description

Transient giant gamma-ray flares comprise the most extreme radiation events to have been observed from magnetars. Developing on (sub)millisecond timescales and expelling vast amounts of energy within a mere fraction of a second, the initial phase of these extraordinary bursts present a significant challenge for candidate trigger mechanisms. Here we revise and critically analyse the spontaneous growth of the relativistic tearing instability in a global magnetospheric current sheet as the trigger mechanism for giant gamma-ray flares. Our main constraints are given by the observed emission timescales [e-folding rise time, peak time (time from the onset of the flare up until the photon flux peaks), and spike time (duration of the initial spike)], the energy output of the giant flare spike, and inferred dipolar magnetic field strengths. From pressure balance and energy conservation considerations we derive a typical current sheet thickness 10^4 cm and height of the reconnection region 10^7 cm, which results in an average reconnection speed (rate at which field lines are advected into the diffusion region) 10^(-3)c for the three observed giant flares. We further discuss the viability of the assumption that the e-folding emission timescale may be equated with the growth time of an MHD instability; it is not self-evident that the radiation would be generated and escape from the system simultaneously as the instability develops.

Primary author

Mr Chris Elenbaas (University of Amsterdam)

Co-author

Dr Anna Watts (University of Amsterdam)

Presentation materials

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