An X-ray periodicity of $\sim$1.8 hours in a narrow-line Seyfert 1 galaxy Mrk 766

TL;DR

This paper reports the detection of a significant X-ray quasi-periodic oscillation in the galaxy Mrk 766, revealing a 1.8-hour period that supports the universality of QPO phenomena across black hole systems.

Contribution

It presents the first detection of a 1.8-hour QPO in Mrk 766, linking it to known black hole QPO relations and suggesting transient nature of such signals.

Findings

QPO detected at ~6450 s with 5σ significance

QPO frequency follows the f-QPO-M_BH relation across black holes

Spectral differences correlate with QPO presence

Abstract

In the narrow-line Seyfert 1 galaxy Mrk 766, a Quasi-Periodic Oscillation (QPO) signal with a period of $\sim6450$ s is detected in the \emph{XMM-Newton} data collected on 2005 May 31. This QPO signal is highly statistical significant at the confidence level at $\sim5\sigma$ with the quality factor of $Q=f/\Delta f>13.6$. The X-ray intensity changed by a factor of 3 with root mean square fractional variability of $14.3\%$. Furthermore, this QPO signal presents in the data of all three EPIC detectors and two RGS cameras and its frequency follows the $f_{\rm QPO}$-$M_{\rm BH}$ relation spanning from stellar-mass to supermassive black holes. Interestingly, a possible QPO signal with a period of $\sim4200$ s had been reported in the literature. The frequency ratio of these two QPO signals is $\sim$ 3:2. Our result is also in support of the hypothesis that the QPO signals can be just transient. The spectral analysis reveals that the contribution of the soft excess component below $\sim$ 1 keV is different between epochs with and without QPO, this property as well as the former frequency-ratio are well detected in X-ray BH binaries, which may have shed some lights on the physical origin of our event.