Two Transient X-Ray Quasi-periodic Oscillations Separated by an Intermediate State in 1H 0707-495

Abstract

In the narrow-line Seyfert 1 galaxy 1H 0707-495, recently a transient quasi-periodic oscillation (QPO) signal with a frequency of 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  Hz in a separated X-ray emission phase at the significance level of . The signal is also found fitting an autoregressive model though at a lower significance. The frequency ratio between these two signals is . The analysis of other XMM-Newton measurements of 1H 0707-495 also reveals the presence of the Hz ( Hz) QPO signal on 2007 May 14 (2010 September 17) at the significance level of ( ). The QPO frequency found in this work follows the 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.