We report results of X-ray timing analyses for the low-field magnetar CXOU J164710.2 - 455216 which exhibited multiple outbursts .
We use data taken with NICER , NuSTAR , Chandra , and Neil-Gehrels-Swift telescopes between 2017 and 2018 when the source was in an active state .
We perform semi-phase-coherent timing analyses to measure the spin parameters and a spin-inferred magnetic-field strength ( B _ { s } ) of the magnetar .
Using a semi-phase-coherent method , we infer the magnetic field strengths to be 3 - 4 \times 10 ^ { 13 } G at the observation period ( \sim MJD 58000 ) , and by comparing with previous frequency measurements ( MJD 54000 ) a long-term average value of B _ { s } is estimated to be \approx 4 \times 10 ^ { 13 } G .
So this analysis may add CXOU J164710.2 - 455216 to the ranks of low-field magnetars .
The inferred characteristic age ( \tau _ { c } ) is 1–2 Myr which is smaller than the age of Westerlund 1 , so the magnetar ’ s association with the star cluster is still secure .
For the low dipole field and the large age , recent multiple outbursts observed from the source are hard to explain unless it has strong magnetic multipole components .
We also find timing anomalies around outburst epochs , which suggests that there may be spin-down torque applied to the magnetar near the epochs as was proposed in magnetar models .