  After 6 years of quiescence, Anomalous X-ray Pulsar (AXP) 4U 0142+61 entered
an active phase in 2006 March that lasted several months. During the active
phase, several bursts were detected, and many aspects of the X-ray emission
changed. We report on the discovery of six X-ray bursts, the first ever seen
from this AXP in ~10 years of Rossi X-ray Timing Explorer (RXTE) monitoring.
All the bursts occurred in the interval between 2006 April 6 and 2007 February
7. The bursts had the canonical fast rise slow decay profiles characteristic of
SGR/AXP bursts. The burst durations ranged from 8-3x10^3 s as characterized by
T90,these are very long durations even when compared to the broad T90
distributions of other bursts from SGRs and AXPs. The first five burst spectra
are well modeled by simple blackbodies, with temperature kT ~2-6 keV. However,
the sixth burst had a complicated spectrum consisting of at least three
emission lines with possible additional emission and absorption lines. The most
significant feature was at ~14 keV. Similar 14-keV spectral features were seen
in bursts from AXPs 1E 1048.1-5937 and XTE J1810-197. If this feature is
interpreted as a proton cyclotron line, then it supports the existence of a
magnetar-strength field for these AXPs. Several of the bursts were accompanied
by a short-term pulsed flux enhancement. We discuss these events in the context
of the magnetar model.
