SIMBAD references

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 in the QPO frequency correlates with the change in the X-ray flux with a short time delay. The data specifically suggest a linear dependence between the QPO period and the flux, and this gives important constraints on the QPO models. In particular, it excludes explanation in terms of the orbiting hot spot model close to a black hole. Linear structures such as shocks, spiral waves, or very distant flares are favored.