Magnetic explosions on neutron stars
Magnetars are neutron stars with the highest known magnetic fields. During active phases they emit numerous bright gamma-ray flares. The strong magnetic field gradually twists into an unstable state. Once a tipping point is reached, the field reconfigures rapidly - and the resulting currents generate gamma-rays. What determines the instability point, however, is not known. Stress may build up in the solid crust, or in the magnetosphere of the star. In order to find out what is going on we are studying the flare emission mechanism using both theoretical models and new observations from, for example, the Fermi Gamma-ray Burst Monitor. If we can identify where stress is building up in the star this will teach us about both dense matter physics, and the behaviour of ultra-strong magnetic fields.
Fig. 1: X-rays and Gamma-rays are emitted during a rare giant flare from the magnetar SGR 1806-20 in late 2004. The initial peak was so bright that it saturated detectors on every satellite that observed it. Normally the flares are much shorter, lasting only fractions of a second.
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