Spectral and timing properties of the magnetar CXOU~J164710.2-455216

TL;DR

This study analyzes the spectral and timing evolution of the magnetar CXOU J164710.2-455216 over several years, revealing correlations between flux and spectral hardness, a lower magnetic field than previously thought, and evidence of multiple outbursts.

Contribution

It provides a detailed long-term analysis of the magnetar's spectral and timing properties, including flux evolution, magnetic field estimation, and crustal cooling modeling, based on extensive archival data.

Findings

Spectral hardness correlates with flux levels.

The magnetic field is estimated to be less than 7 x 10^{13} G.

Evidence of a second outburst event.

Abstract

We report on spectral and timing properties of the magnetar CXOU J164710.2-455216 in the massive star cluster Westerlund 1. Using 11 archival observations obtained with Chandra and XMM-Newton over approximately 1000 days after the source's 2006 outburst, we study the flux and spectral evolution of the source. We show that the hardness of the source, as quantified by hardness ratio, blackbody temperature or power-law photon index, shows a clear correlation with the 2--10 keV absorption-corrected flux and that the power-law component flux decayed faster than the blackbody component for the first ~100 days. We also measure the timing properties of the source by analyzing data spanning approximately 2500 days. The measured period and period derivative are 10.610644(17) s (MJD 53999.06) and <4 X 10^{-13} s s^-1 (90% confidence) which imply that the spin-inferred dipolar magnetic field of the source is less than 7 X 10^{13} G. This is significantly smaller than was suggested previously. We find evidence for a second flux increase, suggesting a second outburst between MJDs 55068 and 55832. Finally, based on a crustal cooling model, we find that the source's cooling curve can be reproduced if we assume that the energy was deposited in the outer crust and that the temperature profile of the star right after the 2006 outburst was relatively independent of density.