# X-ray timing studies of the low-field magnetar CXOU J164710.2-455216

## TL;DR

This study analyzes X-ray timing data from multiple telescopes to measure the spin and magnetic properties of the low-field magnetar CXOU J164710.2-455216, revealing its magnetic field strength, age, and possible multipole components.

## Contribution

It provides the first detailed timing analysis of this low-field magnetar, estimating its magnetic field and age, and discussing implications for magnetar models with low dipole fields.

## Key findings

- Magnetic field strength estimated at 3-4×10^13 G during 2017-2018.
- Characteristic age of 1-2 million years, younger than Westerlund 1.
- Timing anomalies near outbursts suggest spin-down torque effects.

## Abstract

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 $3-4\times 10^{13}\rm \ G$ 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 $\approx4\times 10^{13}\rm \ G$. 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.