New long-term braking index measurements for glitching pulsars using a glitch-template method

TL;DR

This paper introduces a new method to measure the long-term braking indices of glitching pulsars, revealing low indices that suggest these pulsars are older than previously thought and highlighting the impact of glitches on their evolution.

Contribution

The paper presents a novel glitch-template method for measuring pulsar braking indices, overcoming short-term noise effects, and provides new insights into pulsar evolution and age estimates.

Findings

Young glitching pulsars tend to have low braking indices (≤2).

Inter-glitch evolution shows large braking indices (>10).

Some pulsars may be significantly older than their characteristic ages.

Abstract

Braking index measurements offer the opportunity to explore the processes affecting the long-term spin evolution of pulsars and possible evolutionary connections between the various pulsar populations. For young pulsars the long-term trends are generally obscured by short term phenomena such as timing noise and the recoveries form large glitches. Here we present a new method to overcome the latter and report on braking index measurements for the Vela-like pulsars PSR B1800-21 and PSR B1823-13, an updated measurement for Vela and new estimates for four more glitching pulsars observed at Jodrell Bank Observatory. The values of braking indices describe the long-term evolution of the pulsars across the P-P' diagram. Despite some measurements being affected by considerable uncertainties, there is evidence for a common trend involving low braking indices (n<=2) among young glitching pulsars. Such values introduce a new variant in the evolution of young pulsars and their relationship with other populations in the P-P' diagram. Low braking indices also imply that these pulsars could be a few times older than their characteristic ages. We consider PSR B1757-24 and conclude that the pulsar could be old enough to be related to the supernova remnant G5.4-1.2. Between glitches, the short-term evolution of Vela-like pulsars is characterised by large inter-glitch braking indices n_ig > 10. We interpret both short and long term trends as signatures of the large glitch activity, and speculate that they are driven by short-term post-glitch re-coupling and a cumulative long-term decoupling of superfluid to the rotation of the star.