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Re-observing the NLS1 galaxy RE J1034+396 – II. New insights on the soft X-ray excess, QPO, and the analogy with GRS 1915+105

Jin, Chichuan and Done, Chris and Ward, Martin (2021) 'Re-observing the NLS1 galaxy RE J1034+396 – II. New insights on the soft X-ray excess, QPO, and the analogy with GRS 1915+105.', Monthly notices of the Royal Astronomical Society, 500 (2). pp. 2475-2495.


The active galactic nucleus (AGN) RE J1034+396 displays the most significant X-ray quasi-periodic oscillation (QPO) detected so far. We perform a detailed spectral-timing analysis of our recent simultaneous XMM–Newton, NuSTAR, and Swift observations. We present the energy dependence of the QPO’s frequency, rms, coherence, and phase lag, and model them together with the time-averaged spectra. Our study shows that four components are required to fit all the spectra. These components include an inner disc component (diskbb), two warm corona components (CompTT-1 and CompTT-2), and a hot corona component (nthComp). We find that diskbb, CompTT-2 (the hotter but less luminous component), and nthComp all contain the QPO signal, while CompTT-1 only exhibits stochastic variability. By fitting the lag spectrum, we find that the QPO in diskbb leads CompTT-2 by 679 s, and CompTT-2 leads nthComp by 180 s. By only varying the normalizations, these components can also produce good fits to the time-averaged and variability spectra obtained from previous observations when QPOs were present and absent. Our multiwavelength study shows that the detectability of the QPO does not depend on the contemporaneous mass accretion rate. We do not detect a significant Iron K α emission line, or any significant reflection hump. Finally, we show that the rms and lag spectra in the latest observation are very similar to the 67-Hz QPO observed in the micro-quasar GRS 1915+105. These new results support the physical analogy between these two sources. We speculate that the QPO in both sources is due to the expansion/contraction of the vertical structure in the inner disc.

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2020 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:23 October 2020
Date deposited:29 June 2021
Date of first online publication:31 October 2020
Date first made open access:29 June 2021

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