currents, taking energy away, at the same time that pairs are produced. The untwisting timescale is $\sim 1$yr, and it may explain the spectral evolution of some magnetars [@Beloborodov2009].

Timescales {#sec:timecales}
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Changes in magnetars take place during two different timescales. On the one hand, there is a [*secular timescale*]{} of thousands of years during which the magnetar is essentially in equilibrium. On the other hand, there is a [*dynamical timescale*]{} associated to energetic events (burst, flares) that can produce observable variations on timescales as fast as $0.1$s. The latter are likely associated to out-of-equilbrium states.

### Secular timescales {#sec:secular}

The [*secular timescale*]{} is set by the slow magnetothermal evolution of the cooling object. The interior magnetic field evolution is dominated by Hall drift and Ohmic diffusion at the crust [see, e.g. @Vigano2012; @Fujisawa2014 and references therein], which proceeds on typical timescales of $10^3-10^6$ yr. The long-term evolution of the magnetosphere is driven by the changes in the crustal magnetic field, which displaces the footprints of the magnetospheric magnetic field lines. Since this evolution is much slower than the dynamical timescale of the magnetosphere (see below), it can be considered that the magnetosphere evolves through a series of equilibrium states. 