Detection of a non-harmonic QPO precursor to Type-B in the HIMS of MAXI J1820+070 using NICER timing data.
X-Ray Variability Coherence: How to Compute it, What it Means, and How it Constrains Models of Cyg X-1 and GX 339-4
2 Pith papers cite this work. Polarity classification is still indexing.
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abstract
We describe how the coherence function, a Fourier frequency-dependent measure of the linear correlation between time series measured simultaneously in two energy channels, can be used in conjunction with energy spectra, power spectra, and time delays between energy channels to constrain models of the spectrum and variability of x-ray binaries. Here we present a procedure for estimating the coherence function in the presence of counting noise. We apply this method to the black hole candidates Cyg X--1 and GX 339--4, and find that the near perfect coherence between low and high energy x-ray photons rules out a wide range of models that postulate: spatially extended fluctuating emission, thermal flares, and overlapping shot-noise.
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Detection of an imaginary QPO in AT2019wey whose frequency drops from ~5 Hz to ~1 Hz with rising phase lags as the source transitions through HIMS and LHS, showing U-shaped phase-lag spectrum in HIMS.
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Discovery of a quasi-periodic oscillation non-harmonically related to the Type-C QPO in the hard intermedidate state of MAXI J1820+070
Detection of a non-harmonic QPO precursor to Type-B in the HIMS of MAXI J1820+070 using NICER timing data.
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An atypical X-ray variability component in the black hole candidate AT2019wey
Detection of an imaginary QPO in AT2019wey whose frequency drops from ~5 Hz to ~1 Hz with rising phase lags as the source transitions through HIMS and LHS, showing U-shaped phase-lag spectrum in HIMS.