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dc.contributor.advisor Ibrahim, Alaa El Mezeini, Ahmed Monzer
dc.creator El Mezeini, Ahmed Monzer 2010-05-27T14:55:50Z 10000-01-01T14:55:50Z 2010 Spring 2010-05-27T14:55:50Z
dc.description.abstract In this thesis, we present an analysis of highly magnetized neutron stars â magnetarsâ , in search for high frequency oscillations in the recurrent emission from the soft gamma repeater SGR 1806-20, and we discuss the physical interpretation of these oscillations and its implications on the neutron star properties and structure. We present evidence for Quasi-Periodic Oscillations (QPOs) in the recurrent outburst activity from the soft gamma repeater SGR 1806-20 using Rossi X-ray Timing Explorer (RXTE) observations. By searching a large sample of bursts for timing signals at the frequencies of the QPOs discovered in the 2004 December 27 giant flare from the source, we find three QPOs at 84, 103, and 648 Hz in three different bursts. The first two QPOs lie within 8.85% and 11.83%, respectively, from the 92 Hz QPO detected in the giant flare. The third QPO lie within 3.75% from the 625 Hz QPO also detected in the same flare. These QPOs are detected in archival observations that took place eight years before the giant flare. The detected QPOs are found in bursts with different durations, morphologies, and brightness, and are vindicated by Monte Carlo simulations. We also find evidence for candidate QPOs at higher frequencies (1095, 1230, 2785 and 3690 Hz) in other bursts with lower statistical significance. The fact that we can find evidence for QPOs in the recurrent bursts at frequencies relatively close to those found in the giant flare is intriguing and can offer insight about the origin of the oscillations. We confront our findings against the available theoretical models and discuss the physical interpretation of these QPOs. The leading interpretation for the origin of magnetar QPOs suggests that these toroidal seismic oscillatory modes are most likely to be excited by a magnetar crustquake of the neutron star crust. Other models have been proposed to explain the QPO phenomena we observe in magnetars including magnetospheric oscillations, magnetic flux tubes and modes of a passive debris disk. After understanding the real nature of quasi-periodic X-ray oscillations, their observation will be very useful to put stringent constraints on neutron star masses and radii, which define the neutron star equation of state (EOS). We discuss the connection between the QPOs we report and those detected in the giant flares as well as their implications to the neutron star properties. en
dc.format.medium theses en
dc.language.iso en en
dc.rights Author retains all rights with regard to copyright. en
dc.subject.lcsh Thesis (M.S.)--American University in Cairo en
dc.subject.lcsh Neutron stars -- Research.
dc.subject.lcsh Astrophysics.
dc.title Evidence for quasi-periodic oscillations in the recurrent emission from magnetars and their implications on the neutron star properties and equation of state en
dc.type Text en
dc.subject.discipline Department of Physics en
dc.rights.access This item is restricted forever en
dc.contributor.department American University in Cairo. Dept. of Physics en

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  • Theses and Dissertations [1704]
    This collection includes theses and dissertations authored by American University in Cairo graduate students.

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