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Register a new userThe 2006 Outburst of the Magnetar CXOU J164710.2-455216
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We report on data obtained with the Chandra, XMM-Newton, Suzaku and Swift X-ray observatories, following the 2006 outburst of the Anomalous X-ray Pulsar CXO J164710.2-455216. We find no evidence for the very large glitch and rapid exponential decay as was reported previously for this source. We set a 3 sigma upper limit on any fractional frequency increase at the time of the outburst of Delta nu/nu < 1.5 x 10^{-5}. Our timing analysis, based on the longest time baseline yet, yields a spin-down rate for the pulsar that implies a surface dipolar magnetic field of ~9 x 10^{13} G, although this could be biased high by possible recovery from an undetected glitch. We also present an analysis of the source flux and spectral evolution, and find no evidence for long-term spectral relaxation post-outburst as was previously reported.
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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 $3-4times 10^{13}rm G$ 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 $approx4times 10^{13}rm G$. 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 magnetars 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.
Suzaku TOO observation of the anomalous X-ray pulsar CXOU J164710.2-455216 was performed on 2006 September 23--24 for a net exposure of 38.8 ks. During the observation, the XIS was operated in 1/8 window option to achieve a time resolution of 1 s. Pulsations are clearly detected in the XIS light curves with a barycenter corrected pulse period of 10.61063(2) s. The XIS pulse profile shows 3 peaks of different amplitudes with RMS fractional amplitude of ~11% in 0.2--6.0 keV energy band. Though the source was observed with the HXD of Suzaku, the data is highly contaminated by the nearby bright X-ray source GX 340+0 which was in the HXD field of view. The 1-10 keV XIS spectra are well fitted by two blackbody components. The temperatures of two blackbody components are found to be 0.61+/-0.01 keV and 1.22+/-0.06 keV and the value of the absorption column density is 1.73+/-0.03 x 10^{22} atoms cm^{-2}. The observed source flux in 1-10 keV energy range is calculated to be 2.6 x 10^{-11} ergs cm^{-2} s^{-1} with significant contribution from the soft blackbody component (kT = 0.61 keV). Pulse phase resolved spectroscopy of XIS data shows that the flux of the soft blackbody component consists of three narrow peaks, whereas the flux of the other component shows a single peak over the pulse period of the AXP. The blackbody radii changes between 2.2-2.7 km and 0.28-0.38 km (assuming the source distance to be 5 kpc) over pulse phases for the soft and hard components, respectively. The details of the results obtained from the timing and spectral analysis is presented.
We present deep observations of the field of the magnetar CXOJ164710.2-455216 in the star cluster Westerlund 1, obtained in the near-infrared with the adaptive optics camera NACO@VLT. We detected a possible candidate counterpart at the {em Chandra} position of the magnetar, of magnitudes $mathrm{J} = 23.5 pm 0.2$, $mathrm{H} = 21.0 pm 0.1$, and $mathrm{K}_mathrm{S} = 20.4 pm 0.1$. The K$_{rm S}$-band measurements available for two epochs (2006 and 2013) do not show significant signs of variability but only a marginal indication that the flux varied (at the 2 $sigma$ level), consistent with the fact that the observations were taken when CXOJ164710.2-455216 was in quiescence. At the same time, we also present colour--magnitude and colour--colour diagrams in the J, H, and K$_{rm S}$ bands from the 2006 epoch only, the only one with observations in all three bands, showing that the candidate counterpart lies in the main bulk of objects describing a relatively well--defined sequence. Therefore, based on its colours and lack of variability, we cannot yet associate the candidate counterpart to CXOJ164710.2-455216. Future near-infrared observations of the field, following-up a source outburst, would be crucial to confirm the association from the detection of near-infrared variability and colour evolution.
Anomalous X-ray pulsars (AXPs) and soft gamma repeaters (SGRs) are two small classes of X-ray sources strongly suspected to host a magnetar, i.e. an ultra-magnetized neutron star with $Bapprox 10^14-10^15 G. Many SGRs/AXPs are known to be variable, and recently the existence of genuinely transient magnetars was discovered. Here we present a comprehensive study of the pulse profile and spectral evolution of the two transient AXPs (TAXPs) XTE J1810-197 and CXOU J164710.2-455216. Our analysis was carried out in the framework of the twisted magnetosphere model for magnetar emission. Starting from 3D Monte Carlo simulations of the emerging spectrum, we produced a large database of synthetic pulse profiles which was fitted to observed lightcurves in different spectral bands and at different epochs. This allowed us to derive the physical parameters of the model and their evolution with time, together with the geometry of the two sources, i.e. the inclination of the line-of-sight and of the magnetic axis with respect to the rotation axis. We then fitted the (phase-averaged) spectra of the two TAXPs at different epochs using a model similar to that used to calculate the pulse profiles ntzang in XSPEC) freezing all parameters to the values obtained from the timing analysis, and leaving only the normalization free to vary. This provided acceptable fits to XMM-Newton data in all the observations we analyzed. Our results support a picture in which a limited portion of the star surface close to one of the magnetic poles is heated at the outburst onset. The subsequent evolution is driven both by the cooling/varying size of the heated cap and by a progressive untwisting of the magnetosphere.
We observe the magnetar CXOU J171405.7-381031 with XMM-Newton and obtain the most reliable X-ray spectral parameters for this magnetar. After removing the flux from the surrounding supernova remnant CTB~37B, the radiation of CXOU J171405.7-381031 is best described by a two-component model, consisting of a blackbody and power law. We obtain a blackbody temperature of 0.58^{+0.03}_{-0.03} keV, photon index of 2.15^{+0.62}_{-0.68}, and unabsorbed 2-10 keV flux of 2.33^{+0.02}_{-0.02} x 10^{-12} erg cm^{-2} s^{-1}. These new parameters enable us to compare CXOU 171405.7-381031 with other magnetars, and it is found that the luminosity, temperature and the photon index of CXOU J171405.7-381031 are aligned with the known trend among the magnetar population with a slightly higher temperature, which could be caused by its young age. All the magnetars with a spin-down age of less than 1~kyr show time variation or bursts except for CXOU J171405.7-381031. We explore the time variability for ten observations in between 2006 and 2015, but there is no variation larger than sim 10%.
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