Re-observing the NLS1 Galaxy RE J1034+396. I. the Long-term, Recurrent X-ray QPO with a High Significance

Understand

RE J1034+396 is a narrow-line Seyfert 1 galaxy (NLS1) in which the first significant X-ray quasi-periodic oscillation (QPO) in an active galactic nuclei (AGN) was observed in 2007.

• We report the detection of this QPO in a recent XMM-Newton observation in 2018 with an even higher significance.
• The quality factor of this QPO is 20, and its period is 3550 $\pm$ 80 s, which is 250 $\pm$ 100 s shorter than in 2007.
• While the QPO's period has no significant energy dependence, its fractional root-mean-square (rms) variability increases from 4% in 0.3-1 keV to 12% in 1-4 keV bands.