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 - 400910 and 1E 1841 - 045 , respectively .
These observations , part of a larger RXTE AXP monitoring program , have allowed us to study the long-term timing , pulsed flux , and pulse profile evolution of these objects .
We report on four new glitches , one from RXS J170849.0 - 400910 and three from 1E 1841 - 045 .
One of the glitches from 1E 1841 - 045 is among the largest ever seen in a neutron star in terms of fractional frequency increase .
With nearly all known persistent AXPs now seen to glitch , such behavior is clearly generic to this source class .
We show that in terms of fractional frequency change , AXPs are among the most actively glitching neutron stars , with glitch amplitudes in general larger than in radio pulsars .
However , in terms of absolute glitch amplitude , AXP glitches are unremarkable .
We show that the largest AXP glitches observed thus far have recoveries that are unusual among those of radio pulsar glitches , with the combination of recovery time scale and fraction yielding changes in spin-down rates following the glitch similar to , or larger than , the long-term average .
We also observed a large long-term fractional increase in the magnitude of the spin-down rate of 1E 1841 - 045 , following its largest glitch , with \Delta \dot { \nu } / \dot { \nu } = 0.1 .
These observations are challenging to interpret in standard glitch models , as is the frequent occurence of large glitches given AXPs ’ high measured temperatures .
We speculate that the stellar core may be involved in the largest AXP glitches .
Furthermore , we show that AXP glitches appear to fall in two classes : radiatively loud and radiatively quiet .
The latter , of which the glitches of RXS J170849.0 - 400910 and 1E 1841 - 045 are examples , show little evidence for an accompanying radiative event such as a sudden flux increase or pulse profile change .
We also show , however , that pulse profile and pulsed flux changes are common in these AXPs , but do not apprear closely correlated with any timing behavior .