ScholarBank@NUShttps://scholarbank.nus.edu.sgThe DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 28 Nov 2021 22:58:54 GMT2021-11-28T22:58:54Z5031- Quasi-periodic oscillations under wavelet microscope: The application of Matching Pursuit algorithmhttps://scholarbank.nus.edu.sg/handle/10635/115897Title: Quasi-periodic oscillations under wavelet microscope: The application of Matching Pursuit algorithm
Authors: Lachowicz, P.; Done, C.
Abstract: We zoom in on the internal structure of the low-frequency quasi-periodic oscillation (LF QPO) often observed in black hole binary systems to investigate the physical nature of the lack of coherence in this feature. We show the limitations of standard Fourier power spectral analysis for following the evolution of the QPO with time and instead use wavelet analysis and a new time-frequency technique-Matching Pursuit algorithm-to maximise the resolution with which we can follow the QPO behaviour. We use the LF QPO seen in a very high state of XTE J1550-564 to illustrate these techniques and show that the best description of the QPO is that it is composed of multiple independent oscillations with a distribution of lifetimes but with constant frequency over this duration. This rules out models where there is continual frequency modulation, such as multiple blobs spiralling inwards. Instead it favours models where the QPO is excited by random turbulence in the flow. © 2010 ESO.
Thu, 10 Jun 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1158972010-06-10T00:00:00Z
- A ∼4.6 h quasi-periodic oscillation in the BL Lacertae PKS 2155-304?https://scholarbank.nus.edu.sg/handle/10635/111308Title: A ∼4.6 h quasi-periodic oscillation in the BL Lacertae PKS 2155-304?
Authors: Lachowicz, P.; Gupta, A.C.; Gaur, H.; Wiita, P.J.
Abstract: We report a possible detection of an ∼4.6-h quasi-periodic oscillation (QPO) in the 0.3-10 keV emission of the high-energy peaked blazar PKS 2155-304 from a 64 ks observation by the XMM-Newton EPIC/pn detector. We identify a total modulation of ∼5% in the light curve and confirm that nominal period by periodogram, structure function, and wavelet analyses. The limited light curve duration allows the capture of only 3.8 cycles of this oscillation and thus precludes a very strong claim for this QPO, despite a nominally high (≳3σ) statistical significance. We briefly discuss models capable of producing an X-ray QPO of such a period in a blazar. © 2009 ESO.
Sun, 01 Nov 2009 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1113082009-11-01T00:00:00Z
- The model constraints from the observed trends for the quasi-periodic oscillation in RE J1034+396https://scholarbank.nus.edu.sg/handle/10635/116637Title: The model constraints from the observed trends for the quasi-periodic oscillation in RE J1034+396
Authors: Czerny, B.; Lachowicz, P.; Dovčiak, M.; Karas, V.; Pecháček, T.; Das, T.K.
Abstract: We analyze the time variability of the X-ray emission of RE J1034+396 - an active galactic nucleus with the first firm detection of a quasi-periodic oscillations (QPO). Based on the results of a wavelet analysis, we find a drift in the QPO central frequency. The change in the QPO frequency correlates with the change in the X-ray flux with a short time delay. The data specifically suggest a linear dependence between the QPO period and the flux, and this gives important constraints on the QPO models. In particular, it excludes explanation in terms of the orbiting hot spot model close to a black hole. Linear structures such as shocks, spiral waves, or very distant flares are favored. © 2010 ESO.
Wed, 01 Dec 2010 00:00:00 GMThttps://scholarbank.nus.edu.sg/handle/10635/1166372010-12-01T00:00:00Z