X-ray spectroscopy of neutron star low-mass X-ray binaries

In this thesis, I present work spanning a variety of topics relating to neutron star lowmass X-ray binaries (LMXBs) and utilize spectral information from X-ray observations to further our understanding of these sources. First, I give an overview of important X- ray astrophysics relevant to the work I present in subsequent chapters, as well as information about the X-ray observatories from which I obtained my data. In the next three chapters, I consider spectra-both high- and low-resolution--of accretion-powered millisecond X-ray pulsars, a unique and relatively new class of objects. In addition to analysis of the pulsar XTE J1814-338, I compare a broader sample of pulsars with a sample of atoll sources in order to better understand why the latter class do not contain persistently pulsating neutron stars. In particular, I test the hypothesis that pulsations in the atoll sources are suppressed by a high-optical- depth scattering region. Using X-ray color-color diagrams to define a selection criterion based on spectral state, I analyze Rossi X-ray Timing Explorer (RXTE) spectra from all the sources, and use a Comptonization model to obtain measurements of their optical depths. I then discuss efforts to spatially resolve X-ray jets from the accretion-powered millisecond pulsar SAX J1808.4-3658 and the Z source XTE J1701-462. Each was observed by the Chandra X-ray Observatory to produce a high-spatial-resolution image. This work was motivated in part by my analysis of XTE J1814-338, which found an apparent excess of infrared flux which could be attributed to jet emission. Next, I discuss the measured temperatures of thermonuclear X-ray bursts. The detection of line features in these bursts, and hence from the surfaces of neutron stars, has been an important goal for high-resolution X-ray spectroscopy. A measurement of the wavelengths of identified line features would yield a measurement of the neutron star's gravitational redshift, which would help constrain current models for the neutron star equation of state.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Physics.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2007

Author dc:creator

• Krauss, Miriam Ilana

Advisor dc:contributor.advisor

• Deepto Chakrabarty.

• Physics.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/45408

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/45408