X-ray emission from millisecond pulsars
By: by Slavko Bogdan Bogdanov
Published: 2008
Language: eng
Number of pages: 170
Description: We present a comprehensive study of the X-ray emission properties of rotation-powered millisecond pulsars (MSPs). We conduct a detailed analysis of X-ray observations of the complete sample of MSPs in the globular cluster 47 Tucanae with known positions. The X-rays from the majority of these pulsars are well described by a soft, thermal spectrum, similar to what is seen in many nearby field MSPs. We investigate the X-ray emission from two peculiar globular cluster binary MSPs that appear to be the result of a past dynamical binary exchange encounter. The winds of these "exchanged" MSPs are interacting with matter from their unevolved companions and exhibit striking similarities to accreting X-ray MSPs in quiescence, providing unique insight into the behavior of pulsars transitioning from accretion- to rotation-power. We examine the impact of inverse Compton scattering of the thermal X-ray emission from MSP polar caps and find that this effect may account for the hard X-ray tail seen in the spectrum of the nearest known MSP, PSR J0437-4715. We develop a model of thermal X-ray emission from hot spots on the surface of a rotating compact star with an unmagnetized light-element atmosphere. Application to spectroscopic and timing observations of the three nearest known MSPs reveals that the thermal emission from these pulsars is fully consistent with such a model, enabling constraints on important properties of the underlying neutron stars.

The observed thermal pulsations from these MSPs are found to be incompatible with blackbody emission and require the presence of an optically thick, light-element atmosphere on the stellar surface. The morphology of the X-ray pulses profile is consistent with a dipole configuration of the pulsar magnetic field but in at least one case suggests an off-center magnetic axis. Most importantly, this modeling permits interesting limits on the allowed mass-to-radius ratios of these NSs. We also employ this model to place strong constraints on magnetic field evolution models. We discuss the implications of these results on the present understanding of the X-ray emission properties of MSPs and neutron stars, in general.
Notes: "October 2007."

Thesis (Ph.D., Dept. of Astronomy)--Harvard University, 2008.

Includes bibliographical references.