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Behavior of low-mass X-ray binaries and their formation in globular clusters Open Access


Other title
X-ray binaries
Globular clusters
Neutron stars
Black holes
X-ray astronomy
Type of item
Degree grantor
University of Alberta
Author or creator
Bahramian, Arash
Supervisor and department
Heinke, Craig (Physics)
Examining committee member and department
Sivakoff, Gregory (Physics)
Ivanova, Nathalia (Physics)
Pogosyan, Dmitri (Physics)
Verbunt, Franciscus (Radboud University, the Netherlands)
Department of Physics

Date accepted
Graduation date
2016-06:Fall 2016
Doctor of Philosophy
Degree level
Low mass X-ray binaries (LMXBs) are systems of compact stellar remnants accreting from a low mass companion star. These systems show various levels of mass transfer on various timescales. Many aspects of accretion in these systems are still not fully understood, specifically the emission processes involved in various states of mass transfer. The population of LMXBs has been found to be orders of magnitude higher (per unit mass) in globular clusters (GCs) compared to the Galactic field. This overabundance has been explained as due to the formation of LMXBs by stellar encounters in GCs. In this thesis, we study GC LMXB populations, and the details of accretion in these systems. First, we focus on the population of LMXBs and the role of stellar encounters in their formation in GCs. We calculate model-independent stellar encounter rates for 124 Galactic GCs, and show that core-collapsed clusters tend to have lower numbers of LMXBs compared to other clusters with similar values of the stellar encounter rate. Then, we focus on studying accretion in LMXBs in various classes of systems (quiescent, transient, ultra-compact and symbiotic). We provide evidence for the presence of low-level accretion in the rise and decay of outbursts in transient LMXBs, and the absence of low-level accretion in many quiescent neutron star LMXBs. Finally we study two peculiar LMXBs, and show that one is an ultra-compact X-ray binary, and another one is a symbiotic X-ray binary.
This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for the purpose of private, scholarly or scientific research. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
Citation for previous publication
A. Bahramian, C. Heinke, G. Sivakoff, and J. Gladstone 2013, "Stellar Encounter Rate in Galactic Globular Clusters'', ApJ, 766, 136A. Bahramian, C. Heinke, G. Sivakoff, D. Altamirano, R. Wijnands, J. Homan, M. Linares, D. Pooley, N. Degenaar and J. Gladstone 2014, "Discovery of the Third Transient X-ray Binary in the Galactic Globular Cluster Terzan 5'', ApJ, 780, 127A. Bahramian, C. Heinke, N. Degenaar, L. Chomiuk, R. Wijnands, J. Strader, W. Ho and D. Pooley 2015, "Limits on thermal variations in a dozen quiescent neutron stars over a decade'', MNRAS, 452, 3475A. Bahramian, C. Heinke, J. Gladstone, R. Wijnands, R. Kaur and D. Altamirano 2014, "Revealing a new symbiotic X-ray binary with Gemini Near-infrared Integral Field Spectrograph'', MNRAS, 441, 640

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