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A Clash of Clusters Provides New Clue to Dark Matter
Special ACKS Seminar: Dragan Huterer
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ACKS Seminar by Chris Thompson (CITA, Canada)
| What | ACKS |
|---|---|
| When |
21 August 08 from 04:00 pm to 05:00 pm |
| Where | SLAC, 3rd Floor KAVLI Conf Room |
| Contact Name | Lukasz Stawarz |
| Contact Email | stawarz@slac.stanford.edu |
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Electrodynamics of Magnetars
Magnetars are neutron stars with magnetic fields 10-100 times stronger than the QED value (me2/e = 4.4 x 1013 G). The decay of this magnetic field drives impulsive bursts of X-rays and gamma rays, as well as strong persistent emission. In most magnetars, the rate of release of magnetic energy is 100-1000 times higher than the loss of rotational energy to a relativistic wind. Much of the bizarre behavior of magnetars can be understood in terms of deformations of the external magnetic field by instabilities of the neutron star's rigid crust, which have the effect of diverting electric currents from the interior of the star into the closed magnetosphere. This talk will describe recent published work on the mechanism of pair creation and voltage regulation in two distinct zones: close to the star, and in the outer magnetosphere. The behavior of the inner circuit (10-100 km) is similar to that of a relativistic double layer. The current-carrying charges leave a direct imprint on the pulsed X-ray emission through cyclotron scattering, which can be calculated using a Monte Carlo approach. The behavior of the outer circuit is probed by measurements of pulsed radio emission, which is unusually variable and strong at high frequencies in some magnetars. Two novel circuit models are constructed: one in which pair creation is distributed more broadly than in standard pulsar gap models, but the voltage is quite modest; and a second in which strong particle heating is driven by resistive instabilities in the outer magnetosphere. I show that two-stream instabilities (a promising source of radio emission) are sensitive to the magnitude of the current flowing through the circuit.
REFs: Beloborodov & Thompson 2007, ApJ, 657, 967; Fernandez & Thompson 2007, ApJ, 660, 615; Thompson 2008a,b, ApJ, in press.
Fermi Lunch - Richard Dubois