  After at least 6 years of quiescence, Anomalous X-ray Pulsar (AXP) 4U 0142+61
entered an active phase in 2006 March that lasted several months and included
six X-ray bursts as well as many changes in the persistent X-ray emission. The
bursts, the first seen from this AXP in >11 years of Rossi X-ray Timing
Explorer monitoring, all occurred in the interval between 2006 April 6 and 2007
February 7. The burst durations ranged from 0.4-1.8\times103 s. The first five
burst spectra are well modeled by blackbodies, with temperatures kT ~ 2-9 keV.
However, the sixth burst had a complicated spectrum that is well characterized
by a blackbody plus two emission features whose amplitude varied throughout the
burst. The most prominent feature was at 14.0 keV. Upon entry into the active
phase the pulsar showed a significant change in pulse morphology and a likely
timing glitch. The glitch had a total frequency jump of (1.9\pm0.4)\times10-7
Hz, which recovered with a decay time of 17\pm 2 days by more than the initial
jump, implying a net spin-down of the pulsar. Within the framework of the
magnetar model, the net spin-down of the star could be explained by regions of
the superfluid that rotate slower than the rest. The bursts, flux enhancements,
and pulse morphology changes can be explained as arising from crustal
deformations due to stresses imposed by the highly twisted internal magnetic
field. However, unlike other AXP outbursts, we cannot account for a major twist
being implanted in the magnetosphere.
