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Magnetospheric "anti-glitches" in magnetars

We attribute the rapid spindown of magnetar 1E 2259+586 observed by Archibald et al. (2013), termed the "anti-glitch", to partial opening of the magnetosphere during the X-ray burst, followed by changes of the structure of the closed field line region. To account for the observed spin decrease during the X- ray flare all that is needed is the transient opening, for just one period, of a relatively small fraction of the magnetosphere, of the order of only few percent. More generally, we argue that in magnetars all timing irregularities have magnetospheric origin and are induced either by (i) the fluctuations in the current structure of the magnetosphere (similar to the long term torque variations in the rotationally powered pulsars); or, specifically to magnetars, by (ii) opening of a fraction of the magnetosphere during bursts and flares - the latter events are always accompanied by rapid spindown, an "anti-glitch". Slow rotational motion of the neutron star crust, driven by crustal magnetic fields, leads beyond some twist limit to explosive instability of the external magnetic fields and transient opening of a large magnetic flux in a CME-type event, the post-flares increase of magnetospheric currents accompanied by enhanced X-luminosity and spindown rate, changing profiles, as well as spectral hardening, all in agreement with the magnetospheric model of torque fluctuations.