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)


Nordita, Stockholm

Poster Workshop, August 10-14


Mr Chris Elenbaas (University of Amsterdam)


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)


Dr Anna Watts (University of Amsterdam)

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