QPO in RE J1034+396: model constraints from observed trends
  We analyze the time variability of the X-ray emission of RE J1034+396, an active galactic nucleus with the first firm detection of a quasi-periodic oscillations (QPO). Based on the results of a wavelet analysis, we find a drift in the QPO central frequency. The change inthe QPO frequency correlates with the change in the X-ray flux with a short time delay. Linear structures such as shocks, spiral waves, orvery distant flares seem to be a favored explanation for this particular QPO event. 
B. Czerny, P. Lachowicz, M. Dovciak, V. Karas, T. Pechacek, Tapas K.   Das
astro-ph.CO astro-ph.HE