On the connection between radiative outbursts and timing irregularities in magnetars

Abstract

Magnetars are strongly magnetized pulsars and they occasionally show violent radiative outbursts. They also often exhibit glitches that are sudden changes in the spin frequency. It was found that some glitches were associated with outbursts but their connection remains unclear. We present a systematic study to identify possible correlations between them. We find that the glitch size of magnetars likely shows a bimodal distribution, different from the distribution of the Vela-like recurrent glitches but consistent with the high-end of that of normal pulsars. A glitch is likely a necessary condition for an outburst but not a sufficient condition because only 30% of glitches were associated with outbursts. In the outburst cases, the glitches tend to induce larger frequency changes compared to those unassociated ones. We argue that a larger glitch is more likely to trigger the outburst mechanism, either by reconfiguration of the magnetosphere or deformation of the crust. A more frequent and deeper monitoring of magnetars is necessary for further investigation of their connection.

Pulsar glitches: observations and physical interpretation

“…For normal pulsars, glitch activity does not seem to depend on the inferred surface magnetic field [157]. Glitch sizes Δν of magnetars are not exceptional [275], but in line with expectations for their ν values, and it is only when considering Δν/ν values that magnetar glitches appear particularly large because of their low spin frequencies. The modest Δν of magnetars can also be explained by the fact that they are young neutron stars and the decay of their high magnetic fields provides a powerful heating source, potentially preventing large lags ω from building up.…”

“…by twisting of magnetic field lines which are anchored to the crust [274]). The aforementioned study of five magnetars concluded that about 20%-30% of glitches and timing anomalies can be associated with radiative changes ([98], also [275]), and that the size (or any other property) of the glitches is irrelevant with respect to the presence or lack of a radiative counterpart. However, later studies using an extended dataset, found a possible tendency for events related to X-ray outbursts to involve larger frequency changes [275].…”