2017ApJ...849..138K

We present a statistical characterization of the γ-ray emission from the four Fermi-LAT sources: FR I radio galaxy NGC 1275, BL Lac Mrk 421, FSRQs B2 1520+31, and PKS 1510-089 detected almost continuously over a time integration of three days between 2008 August and 2015 October. The observed flux variation is large, spanning 2 orders of magnitude between the extremes, except for Mrk 421. We compute the flux distributions and compare with Gaussian and lognormal ones. We find that the three blazars have distributions consistent with a lognormal, suggesting that the variability is of a nonlinear, multiplicative nature. This is further supported by the computation of the flux-rms relation, which is observed to be linear for the three blazars. However, for NGC 1275, the distribution does not seem to be represented either by a lognormal or a Gaussian, while its flux-rms relation is still found to be linear. We also compute the power spectra, which suggest the presence of a break, but are consistent with typical scale-free power-law shot noise. The results are broadly consistent with the statistical properties of the magnetic reconnection powered minijets-in-a-jet model. We discuss other possible scenarios and implications of these observations on jet processes and connections with the central engine.