  After two major outbursts in 2006 and 2011, on 2017 May 16 the magnetar CXOU
J164710.2-455216, hosted within the massive star cluster Westerlund I, emitted
a short (20 ms) burst, which marked the onset of a new active phase. We started
a long-term monitoring campaign with Swift (45 observations), Chandra (5
observations) and NuSTAR (4 observations) from the activation until 2018 April.
During the campaign, Swift BAT registered the occurrence of multiple bursts,
accompanied by two other enhancements of the X-ray persistent flux. The long
time span covered by our observations allowed us to study the spectral as well
as the timing evolution of the source. After 11 months since the 2017 May
outburst onset, the observed flux was about 15 times higher than its historical
minimum level and a factor of 3 higher than the level reached after the 2006
outburst. This suggests that the crust has not fully relaxed to the quiescent
level, or that the source quiescent level has changed following the multiple
outburst activities in the past 10 years or so. This is another case of
multiple outbursts from the same source on a yearly time scale, a somehow
recently discovered behaviour in magnetars.
