2018ApJ...853..193Z

In the narrow-line Seyfert 1 galaxy 1H 0707-495, recently a transient quasi-periodic oscillation (QPO) signal with a frequency of ∼2.6×10^–4 Hz has been detected at a high statistical significance. Here, we reanalyze the same set of XMM-Newton data observed on 2008 February 4 with the weighted-wavelet Z-transform method. In addition to confirming the previous findings, we also find another QPO signal with a frequency of ∼1.2×10^–4 Hz in a separated X-ray emission phase at the significance level of ∼3.7σ . The signal is also found fitting an autoregressive model though at a lower significance. The frequency ratio between these two signals is ∼2:1. The analysis of other XMM-Newton measurements of 1H 0707-495 also reveals the presence of the ∼2.6×10^–4 Hz (∼1.2×10^–4 Hz) QPO signal on 2007 May 14 (2010 September 17) at the significance level of ∼4.2σ (∼3.5σ ). The QPO frequency found in this work follows the f_QPO-M_BH relation reported in previous works spanning from stellar mass to supermassive black holes. This is the first observation of two separated transient X-ray QPO signals in active galactic nuclei, which sheds a new light on the physics of accreting supermassive black holes.