Characterizing Intermittency of 4-Hz Quasi-periodic Oscillation in XTE J1550-564 using Hilbert-Huang Transform

We present the time-frequency analysis results based on the Hilbert-Huang transform (HHT) for the evolution of a 4-Hz low-frequency quasi-periodic oscillation (LFQPO) around the black hole X-ray binary XTE J1550-564. The origin of LFQPOs is still debated. To understand the cause of the peak broadening, we utilized a recently developed time-frequency analysis, HHT, for tracking the evolution of the 4-Hz LFQPO from XTE J1550 564. By adaptively decomposing the ~4-Hz oscillatory component from the light curve and acquiring its instantaneous frequency, the Hilbert spectrum illustrates that the LFQPO is composed of a series of intermittent oscillations appearing occasionally between 3 Hz and 5 Hz. We further characterized this intermittency by computing the confidence limits of the instantaneous amplitudes of the intermittent oscillations, and constructed both the distributions of the QPO's high and low amplitude durations, which are the time intervals with and without significant ~4-Hz oscillations, respectively. The mean high amplitude duration is 1.45 s and 90% of the oscillation segments have lifetimes below 3.1 s. The mean low amplitude duration is 0.42 s and 90% of these segments are shorter than 0.73 s. In addition, these intermittent oscillations exhibit a correlation between the oscillation's rms amplitude and mean count rate. This correlation could be analogous to the linear rms-flux relation found in the 4-Hz LFQPO through Fourier analysis. We conclude that the LFQPO peak in the power spectrum is broadened owing to intermittent oscillations with varying frequencies, which could be explained by using the Lense-Thirring precession model.Comment: 27 pages, 9 figures, accepted for publication in The Astrophysical Journa

The Effect of Congressional Sessions on the Stock Market in Emerging Democracy: the Case of Taiwan

Political uncertainty, Congressional effect, Volatility asymmetry, EGARCH-M

The Rhetoric of Exile in the Preaching and Teaching of the Anglo-Saxon Church: Glimpses of the Cultural Ideology in Old English Homilies

Abstract. This article explores how the early medieval vernacular homiletic discourse produced in Anglo-Saxon England strategically employs the rhetoric exile, a theme whose significance is also articulated widely in Old English poetry. As words denoting such similar ideas as exile, banishment, exclusion, casting/driving out, etc., recur significantly in the homilies of the Anglo-Saxon Church, including the homilies of Ælfric, Wulfstan, and the Blickling and Vercelli Codices, I propose an analysis of the instances in which the rhetoric about exile is used in preaching and theology in order to reveal not only the Church authors/teachers’ ability and effort to translate Latin and to disseminate complex theological ideas in their vernacular tongue, but also certain aspects of the broader cultural ideology in the culture of Anglo-Saxon England