Quarks and Compact Stars (QCS)
Oct. 20-22, 2014, KIAA at Peking University, Beijing - P. R. China

Anti-glitch due to collision of a planetesimal with the magnetar 1E 2259+586

Yongfeng Huang

Nanjing University

Abstract: Magnetars are strongly magnetized neutron stars whose surface magnetic fields can be several hundred times as strong as that of typical radio pulsars. Glitches have been frequently observed in both normal pulsars and magnetars. Previously these glitches unexceptionally manifest as sudden spin-ups that are usually explained as due to impulsive transfer of angular momentum from the interior superfluid component (whose angular velocity is slightly higher) to the outer solid crust (which rotates slightly slower). Alternatively, such spin-up glitches may also result from large-scale crust-cracking events. However, recently an unprecedented anti-glitch from the magnetar 1E 2259+586 was reported. In this case, the magnetar clearly exhibited a sudden spin-down, strongly challenging the glitch theory for all neutron stars. Here we show that this anti-glitch can be well explained by a nearly head-on collision of a small solid body with the magnetar. The intruder has a mass of ~ 10^21 g. Its orbital angular momentum is assumed to be just antiparallel to the momentum of the spinning magnetar, so that the sudden spin-down can be naturally accounted for. The observed hard X-ray burst and decaying softer X-ray emission associated with the anti-glitch can also be reasonably explained. Our study indicates that a completely different type of glitches as due to collisions between small bodies and neutron stars should exist and may have already been observed previously. It also hints a new way for studying the capture events by neutron stars: through accurate timing observations of pulsars. (For more details, see: Huang & Geng, 2014, ApJ, 782, L20.)