AGN Variability at High Energies

I discuss the origin of the X-ray and gamma-ray variability in AGNs, particularly blazars such as 3C 273 and 3C 279. In the X-ray band, blazars behave very much like Seyfert galaxies (ie., non-beamed AGN): like the rms-flux relation and the shape of the Power Spectral Density (PSD). The implication is that the perturbations propagate inwards through the accretion disc and also modulate the X-ray emission region in blazars. The gamma-ray lightcurves are, however, very different to those in the X-ray band, implying separate emission regions in both bands. This is incompatible with the assumption that the X-ray and gamma-ray emissions come from a steady jet. I discuss the  implications of these results and the possible future observations to clarify the situation.