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Timing and spectral studies of the peculiar x-ray binary Circinus X-1

Posted on:2004-08-12Degree:Ph.DType:Dissertation
University:Stanford UniversityCandidate:Parkinson, Pablo Miguel SazFull Text:PDF
GTID:1468390011474643Subject:Physics
Abstract/Summary:
Cir X-1 is a unique Galactic X-ray binary which was initially classified as a black hole candidate but later reclassified as a neutron star due primarily to the observation of Type I X-ray Bursts by EXOSAT in 1985.; In this work, I examine the timing and spectral properties of Cir X-1. FFT analyses are used to study the short (<1 s) timescales while Lomb-Scargle and Phase Dispersion Minimization periodograms are computed to study longer timing properties.; I analyze Quasi-Periodic Oscillations (QPO) in the 1-50 Hz range and divide them into lower frequency (∼3–20 Hz) and higher frequency ones (∼15–50 Hz). The high frequency QPOs decrease in strength (% rms) with increasing frequency, while the lower frequency ones stay constant. The energy dependence of the QPOs implies the frequency is not representative of different locations in the disk.; The power spectrum of Cir X-1 in its softest state is compared to Cyg X-1. Both show breaks. By using scaling arguments, I hypothesize that Cir X-1 has a mass of ∼3 M , greater than the canonical 1.4 M mass of a neutron star.; I study the energy spectrum evolution of Cir X-1 by constructing both instrument-independent and model-independent color-color diagrams. Spectral fits were performed on USA data, from which physical parameters were derived.; The spectral parameters indicate that a two-component model is valid for describing the Cir X-1 spectrum: a multicolor blackbody emission from an accretion disk and a Comptonized emission from a hot plasma (boundary layer or corona). The temperature of the disk remains constant, while there is an indication that the Comptonizing component increases in temperature with orbital phase. From the relative contribution of the disk I infer the neutron star is spinning very rapidly (>1 kHz).; The long-term variability of Cir X-1 is studied using data from instruments going back over thirty years. I derive an X-ray ephemeris based showing that the period of Cir X-1 decreases rapidly (P/P˙ < 3000 yrs), possibly implying a very young age.; I compute dynamic periodograms and find new, unexplained periodicities. A 250 day segment of data shows no detectable orbital period while displaying a new ∼40 day periodicity. A 335 day super-orbital period is found with hardness ratio perfectly anti-correlated, making it possible that this period is due to an obscuration effect from a precessing orbit.
Keywords/Search Tags:X-1, X-ray, Spectral, Timing, Period
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