Nonlinear interglitch dynamics, the braking index of the Vela pulsar and the time to the next glitch

TL;DR

This paper models the inter-glitch timing of the Vela pulsar using a nonlinear vortex creep model, predicts the next glitch date, and discusses the impact of persistent shifts on glitch timing and braking index estimation.

Contribution

It introduces a modified inter-glitch timing model incorporating persistent shifts, improving predictions of glitch intervals and estimating the braking index for the Vela pulsar.

Findings

The braking index of Vela is estimated at 2.81 +/- 0.12.

The predicted next glitch date is around Dec. 22, 2017, with variations depending on persistent shifts.

The model's prediction was confirmed by an observed glitch 138 days after the forecast.

Abstract

The inter-glitch timing of the Vela pulsar is characterized by a constant second derivative of the rotation rate. This takes over after the post-glitch exponential relaxation, and is completed at about the time of the next glitch. The vortex creep model explains the second derivatives in terms of non-linear response to the glitch. We present inter-glitch timing fits to the present sample covering 16 large glitches, taking into account the possibility that in some glitches part of the step in spin-down rate may involve a "persistent shift", as observed in the Crab pulsar. Modifying the expression for the time between glitches with this hypothesis leads to better agreement with the observed inter-glitch time intervals. We extrapolate the inter-glitch model fits to obtain spin-down rates just prior to each glitch, and use these to calculate the braking index n = 2.81 +/- 0.12. The next glitch should occur around Dec. 22, 2017 +/- 197 days if no persistent shift is involved, but could occur as early as July 27, 2016 +/- 152 days if the 2013 glitch gave rise to a typical Vela persistent shift. Note added: Literally while we were submitting the first version of this paper, on Dec. 12, 2016, we saw ATel # 9847 announcing a Vela pulsar glitch which has arrived 138 days after our prediction with a persistent shift, within the 1 sigma uncertainty of 152 days.