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

TL;DR

This study provides detailed spectral-timing analysis of the AGN RE J1034+396, revealing the components involved in its QPO and drawing parallels with the micro-quasar GRS 1915+105, suggesting a common physical mechanism.

Contribution

It introduces a comprehensive spectral-timing model of RE J1034+396's QPO, identifying multiple corona components and their phase relationships, and compares these with GRS 1915+105.

Findings

QPO involves multiple spectral components including disk and coronae

The QPO phase lag sequence suggests a vertical structure expansion/contraction mechanism

Similarity of QPO properties with GRS 1915+105 supports a common physical origin

Abstract

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 multi-wavelength 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{\alpha} 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.