Pulse profile change possibly associated with a glitch in the anomalous X-ray pulsar 4U 0142+61

We report a glitchlike pulse-frequency deviation from the simple spin-down law in an anomalous X-ray pulsar (AXP), 4U 0142+61, detected by ASCA observations. We also found a significant change in pulse profile after the putative glitch. The glitch parameters resemble those found in another AXP, 1RXS J170849.0-400910, and in the Vela and other radio pulsars. This suggests that radio pulsars and AXPs have the same internal structure and glitch mechanism. It must be noted, however, that the pulse-frequency anomaly can also be explained by a gradual change of the spin-down rate without invoking a glitch.