http://arxiv.org/abs/2007.14704
RE J1034+396 displays the so far detected most significant X-ray Quasi-Periodic Oscillation (QPO) in AGN. We perform a detailed spectral-timing analysis on the data using recent simultaneous XMM-Newton, NuSTAR and Swift observations. We present the detailed energy dependence of the QPO’s frequency, rms, coherence and phase lag. We construct various frequency-resolved variability spectra, which are modelled together with the time-averaged spectra. Our study shows that four components are required to fit all the spectra, including an inner disc component (diskbb), two warm corona components (CompTT-1 and CompTT-2) and a hot corona component (nthComp). An important discovery is that within the two warm corona components, CompTT-2 (the hotter, less luminous component) contains the QPO signal, while the stochastic variability is concentrated in CompTT-1. These components also allow us to fit the lag-energy spectra, as well as being able to describe the previous observation of a strong QPO in 2007, and the absent QPO observations, by varying only the relative normalizations of these components. Our multi-wavelength study shows that the QPO’s detectability does not depend on the contemporaneous mass accretion rate through the outer disc as estimated from the UV flux. We do not detect a significant Iron K$\alpha$ line, nor any significant reflection component hump. Finally, we show that the rms and lag spectra of RE J1034+396 in the recent observation are very similar to the 67 Hz QPO in the micro-quasar GRS 1915+105. These new results reinforce the physical analogy between the two sources. We speculate that the QPO in both sources is due to expansion/contraction of the inner disc vertical structure.
C. Jin, C. Done and M. Ward
Thu, 30 Jul 20
-597/71
Comments: 21 pages, 16 figures, 6 tables, submitted to MNRAS
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