Core and crust contributions in overshooting glitches: the Vela pulsar 2016 glitch

During the spin-up phase of a large pulsar glitch - a sudden decrease of the rotational period of a neutron star - the angular velocity of the star may overshoot, namely reach values greater than that observed for the new post-glitch equilibrium. These transient phenomena are expected on the basis of theoretical models for pulsar internal dynamics and their observation has the potential to provide an important diagnostic for glitch modelling. We present a simple criterion to assess the presence of an overshoot, based on the minimal analytical model that is able to reproduce an overshooting spin-up. We employ it to fit the data of the 2016 glitch of the Vela pulsar, obtaining estimates of the fractional moments of inertia of the internal superfluid components involved in the glitch, of the rise and decay timescales of the overshoot, and of the mutual friction parameters between the superfluid components and the normal one. We study the cases with and without strong entrainment in the crust: in the former, we find indication of a large inner core strongly coupled to the observable component and of a reservoir of angular momentum extending into the core to densities below nuclear saturation, while in the latter a large reservoir extending above nuclear saturation and a standard normal component without inner core are suggested.

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