An anti-glitch in a magnetar

Abstract

Magnetars are neutron stars with X-ray and soft γ-ray outbursts thought to be powered by intense internal magnetic fields. Like conventional neutron stars in the form of radio pulsars, magnetars exhibit 'glitches' during which angular momentum is believed to be transferred between the solid outer crust and the superfluid component of the inner crust. The several hundred observed glitches in radio pulsars and magnetars have involved a sudden spin-up (increase in the angular velocity) of the star, presumably because the interior superfluid was rotating faster than the crust. Here we report X-ray timing observations of the magnetar 1E 2259+586 (ref. 8), which exhibited a clear 'anti-glitch'--a sudden spin-down. We show that this event, like some previous magnetar spin-up glitches, was accompanied by multiple X-ray radiative changes and a significant spin-down rate change. Such behaviour is not predicted by models of neutron star spin-down and, if of internal origin, is suggestive of differential rotation in the magnetar, supporting the need for a rethinking of glitch theory for all neutron stars.

Implications of an anti-glitch in AXP/SGR

“…At a distance (Durant & van Kerkwijk 2006) of 7.5 Kpc the corresponding fluence was 1.5 × 10 −5 erg/cm 2 and flux 1.5 × 10 −11 (10 6 s/τ ) erg/cm 2 -s, consistent with the decaying increment to the 2-10 keV X-ray flux observed by Archibald, et al (2013) following the antiglitch. This increment is also consistent with an accretional explanation of the more rapid spindown during this period of increased flux, and its decay is consistent with the return of the spindown rate to approximately its pre-antiglitch value in the latter half of 2012.…”

“…It is explicable in accretional models. Archibald, et al (2013), in their simplest fit, find the antiglitch magnitude to have been ∆ω ≈ −3 × 10 −7 /s.…”

“…Something other than magnetic dipole moment distinguishes AXP (and by implication SGR) from those neutron stars that, if spinning fast enough, would be radio pulsars. Archibald, et al (2013) discovered an "anti-glitch" in the AXP 1E 2259+586. In -4 -contrast to the glitches of radio pulsars and other AXP, in the anti-glitch the rotation rate suddenly decreased (spin-down).…”

Radio Disappearance of the Magnetar Xte J1810–197 and Continued X-Ray Timing

“…is possible that an anti-glitch (Archibald et al 2013;Şaşmaz Muş et al 2014) and/or change in torque occurred between 2012 May and September. But we cannot tell for sure what happened because the change in frequency differs from the extrapolation by only 2σ.…”

Understanding Recent Magnetar Observations from the Magnetospheric Point of View

“…However, a spin-down glitch (i.e. anti-glitch) is observed in one magnetar 1E 2259+586 [19]. Meanwhile, the X-ray luminosity also increases by about a factor of two during this epoch.…”