2014ApJ...784L..41H

The sudden spin-down in the rotation of magnetar 1E 2259+586 observed by Archibald et al. was a rare event. However, that particular event, referred to as an anti-glitch, was followed by another event, which Archibald et al. suggested could either be a conventional glitch or another anti-glitch. Although there is no accompanying radiation activity or pulse profile change, there is decisive evidence of the existence of a second timing event, judging from the timing data. We apply a Bayesian Model Selection to quantitatively determine which of these possibilities better explains the observed data. We show that the observed data strongly support the presence of two successive anti-glitches with a Bayes factor, often called the odds ratio, greater than 40. Furthermore, we show that the second anti-glitch has an associated frequency change Δν of -8.2x10^–8 Hz. We discuss the implications of these results for possible physical mechanisms behind this anti-glitch.