Glitches in Anomalous X‐Ray Pulsars

Abstract

We report on 8.7 and 7.6 yr of Rossi X-Ray Timing Explorer (RXTE)observations of the anomalous X-ray pulsars (AXPs) RXS J170849.0-400910and 1E 1841-045, respectively. These observations have allowed usto study the long-term timing, pulsed flux, and pulse profile evolutionof these objects. We report on four new glitches, one from RXS J170849.0-400910and three from 1E 1841-045. With nearly all known persistent AXPsnow seen to glitch, such behavior is clearly generic to this sourceclass. We show that in terms of fractional frequency change, AXPsare among the most actively glitching neutron stars, with glitchamplitudes in general larger than in radio pulsars. However, in termsof absolute glitch amplitude, AXP glitches are unremarkable. Unlikeradio pulsar glitches, AXP glitches can sometimes, though not always,be accompanied by radiative events. We show that the largest observedAXP glitches have recoveries that are unusual among those of radiopulsar glitches, with the combination of recovery time scale andfraction yielding changes in spin-down rates following the glitchsimilar to, or larger than, the long-term average. We also observeda large long-term fractional increase in the magnitude of the spin-downrate of 1E 1841-045, following its largest glitch, with {Δ}{ν}{\dot}/{ν}{\dot}=0.1.These observations are challenging to interpret in standard glitchmodels, as is the frequent occurence of large glitches given AXPs'high measured temperatures. We speculate that the stellar core maybe involved in the largest AXP glitches.