Post-glitch exponential relaxation of radio pulsars and magnetars in terms of vortex creep across flux tubes

Abstract

Timing observations of rapidly rotating neutron stars revealed a great number of glitches, observed both from canonical radio pulsars and magnetars. Among them, 76 glitches have shown exponential relaxation(s) with characteristic decay times ranging from several days to a few months, followed by a more gradual recovery. Glitches displaying exponential relaxation with single or multiple decay time constants are analysed in terms of a model based on the interaction of the vortex lines with the toroidal arrangement of flux tubes in the outer core of the neutron star. Model results agree with the observed timescales in general. Thus, the glitch phenomenon can be used to deduce valuable information about neutron star structure, in particular on the interior magnetic field configuration which is unaccessible from surface observations. One immediate conclusion is that the magnetar glitch data are best explained with a much cooler core and therefore require that direct Urca type fast cooling mechanisms should be effective for magnetars.

Neutron star dynamics under time-dependent external torques

“…The approximately constant second derivativeΩ c interglitch timing behaviour observed in the Vela and other pulsars (Akbal et al 2017;Yu et al 2013) corresponds to a uniform density of vortices unpinned at the glitch leading to a range of waiting times throughout the superfluid regions. Two component models with linear or nonlinear internal torques have so far been applied to post-glitch or inter-glitch timing behaviour of radio pulsars (Alpar et al 1993(Alpar et al , 1996Akbal et al 2015Akbal et al , 2017Gügercinoglu 2017), where the external torque, with a secular (characteristic) timescale τ c ≡ Ω c /2|Ω c | ∼ 10 3 − 10 6 yr is constant for timescales of observed postglitch relaxation.…”

“…Typically several distinct components of relaxation with different relaxation times are observed after pulsars glitches (Alpar et al 1996;Akbal et al 2017;Gügercinoglu 2017). After exponential relaxation is over the response to the glitch continues with a constant second derivativeΩ c .…”

Force on a neutron quantized vortex pinned to proton fluxoids in the superfluid core of cold neutron stars

“…Interactions between neutron vortices and proton fluxoids are therefore unavoidable, and are pivotal in the magnetorotational evolution of NSs. In particular, vortices may pin to fluxoids (Muslimov & Tsygan 1985;Sauls 1989;Srinivasan et al 1990;Ruderman et al 1998) (see also Alpar (2017) for a recent review), and this may have important implications for various astrophysical phenomena, such as precession (Sedrakian et al 1999;Link 2006;Glampedakis et al 2008), r-mode instability (Haskell et al 2009(Haskell et al , 2014 and pulsar glitches Sidery & Alpar 2009;Glampedakis & Andersson 2009;Haskell et al 2013;Haskell & Melatos 2015;Gügercinoglu 2017;Sourie et al 2017;Haskell et al 2018;Graber et al 2018). However, the detailed force acting on individual vortices to which fluxoids are pinned remains poorly understood.…”

Stability of interlinked neutron vortex and proton flux tube arrays in a neutron star: equilibrium configurations

“…A static magnetic geometry is impossible in the presence of differential rotation if closed magnetic loops exist inside the star (Easson 1979;Melatos 2012;Glampedakis & Lasky 2015). Flux tubes can also creep outwards in a "lead-ing" manner due to buoyancy forces (Muslimov & Tsygan 1985) or diffusion (Gügercinoglu 2017).…”