The largest glitch observed in the Crab pulsar

Abstract

We have observed a large glitch in the Crab pulsar (PSR B0531+21). The glitch occurred around MJD 58064 (2017 November 8) when the pulsar underwent an increase in the rotation rate of ∆ν = 1.530 × 10 −5 Hz, corresponding to a fractional increase of ∆ν/ν = 0.516 × 10 −6 making this event the largest glitch ever observed in this source. Due to our high-cadence and long-dwell time observations of the Crab pulsar we are able to partially resolve a fraction of the total spin-up of the star. This delayed spinup occurred over a timescale of ∼1.7 days and is similar to the behaviour seen in the 1989 and 1996 large Crab pulsar glitches. The spin-down rate also increased at the glitch epoch by ∆ ν/ ν = 7 × 10 −3 . In addition to being the largest such event observed in the Crab, the glitch occurred after the longest period of glitch inactivity since at least 1984 and we discuss a possible relationship between glitch size and waiting time.No changes to the shape of the pulse profile were observed near the glitch epoch at 610 MHz or 1520 MHz, nor did we identify any changes in the X-ray flux from the pulsar. The long-term recovery from the glitch continues to progress as ν slowly rises towards pre-glitch values. In line with other large Crab glitches, we expect there to be a persistent change to ν. We continue to monitor the long-term recovery with frequent, high quality observations.

NICER observations of the Crab pulsar glitch of 2017 November

“…Theν 0 of Zhang et al (2018) is an factor of two smaller than the value in Table 1. I believe these differences arise from the fact that firstly, the ν values listed by the JBCPME (from which Table 1 is derived) are themselves average values, mostly monthly averages, and secondly the preglitch durations of the three works may differ significantly; this may particularly affect the frequency second derivative. It is therefore concluded that there is broad agreement between the preglitch parameters derived here with those of Shaw et al (2018) and Zhang et al (2018), at least for the purpose of this work.…”

“…The last observation available for this work was on 2019 Apr 26 (ObsID 2013010103, MJD 58599.988), but this had only 34 sec of live time. This kind of nonuniform cadence of observations implies that one can not perform the phase coherent timing analysis that was done by Shaw et al (2018) and Zhang et al (2018). This is particularly true for the glitch that is under discussion; it is so large that the change in phase over a single day can be larger than one cycle so that the cadence required for phase coherent analysis is several timing observations in a single day.…”

“…The values of ν 0 ,ν 0 andν 0 of Shaw et al (2018) are given in their Table 1. Propagating them from their reference epoch to the glitch epoch, their ν 0 differs from the value in Table 1 above by −0.492 micro Hertz (µHz); theirν 0 differs from the above value by 0.042 × 10 −12 Hz/sec.…”

“…On 2017 Nov 8, a timing glitch occurred in the Crab pulsar that was the largest of the glitches so far (Shaw et al 2018). They analyzed data for about 150 days after the glitch, and several hundred days before, and brought about the following conclusions that are relevant for this work.…”

“…The parameters that remain constant across the glitch are the peaks and widths of the main pulse and the inter pulse of the Crab pulsar at 610 and 1520 mega Hertz (MHz) ( Fig. 5 of Shaw et al (2018)). Finally, there is no change in the 2 − 50 kilo electron volt (Kev) X-ray flux on account of the glitch (Fig.…”