A periodicity of ∼1 hour in X-ray emission from the active galaxy RE J1034+396

Active galactic nuclei and quasars are thought to be scaled- up versions of Galactic black hole binaries, powered by accretion onto supermassive black holes with masses of 10(6)-10(9) M., as opposed to the similar to 10 M. in binaries (here M. is the solar mass). One example of the similarities between these two types of systems is the characteristic rapid X- ray variability seen from the accretion flow(1). The power spectrum of this variability in black hole binaries consists of a broad noise with multiple quasi- periodic oscillations superimposed on it. Although the broad noise component has been observed in many active galactic nuclei(2,3), there have hitherto been no significant detections of quasi- periodic oscillations(4-6). Here we report the discovery of an similar to 1- hour X- ray periodicity in a bright active galaxy, RE J1034+396. The signal is highly statistically significant ( at the 5.6 sigma level) and very coherent, with quality factorQ > 16. The X- ray modulation arises from the direct vicinity of the black hole.