The Chandra X-ray Spectrum of the 10.6 s Pulsar in Westerlund 1: Testing the Magnetar Hypothesis

Abstract

Two sensitive Chandra X-ray observations of the heavily-reddened galactic starburst cluster Westerlund 1 in May and June 2005 detected a previously unknown X-ray pulsar (CXO J164710.20-455217). Its slow 10.6 s pulsations, moderate X-ray temperature kT $\approx$ 0.5 keV, and apparent lack of a massive companion tentatively suggest that it is an Anomalous X-ray Pulsar (AXP). An isothermal blackbody model yields an acceptable spectral fit but the inferred source radius is much less than that of a neutron star, a result that has also been found for other AXPs. We analyze the X-ray spectra with more complex models including a model that assumes the pulsar is a strongly magnetized neutron star (``magnetar'') with a light element atmosphere. We conclude that the observed X-ray emission cannot be explained as global surface emission arising from the surface of a cooling neutron star or magnetar. The emission likely arises in one or more localized regions (``hot spots'') covering a small fraction of the surface. We discuss these new results in the context of both accretion and magnetar interpretations for the X-ray emission.

arXiv comment14 pages, 5 figures; to appear in ApJ

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Cited by in corpus (10)

• Intermediate to low-mass stellar content of Westerlund 1
• The Post-Burst Awakening of the Anomalous X-ray Pulsar in Westerlund 1
• From outburst to quiescence: the decay of the transient Anomalous X-ray Pulsar XTE J1810-197
• A VLT/FLAMES survey for massive binaries in Westerlund 1: I. first observations of luminous evolved stars
• Constraints on the Emission and Viewing Geometry of the Transient Anomalous X-ray Pulsar XTE J1810-197
• Emission geometry, radiation pattern, and magnetic topology of the magnetar XTE J1810-197 in its quiescent state
• Spectral and timing properties of the magnetar CXOU~J164710.2-455216
• The imprint of the crustal magnetic field on the thermal spectra and pulse profiles of isolated neutron stars
• The multi-outburst activity of the magnetar in Westerlund I
• Suzaku Observation of the Anomalous X-ray Pulsar CXOU J164710.2--455216