Systematic Search for Long-Term Trends in Fermi-LAT Jetted Active Galactic Nuclei

Jetted Active Galactic Nuclei (AGN) exhibit variability across a wide range of time scales. Traditionally, this variability can often be modeled well as a stochastic process. However, in certain cases, jetted AGN variability displays regular patterns, enabling us to conduct investigations aimed at understanding its origins. Additionally, a novel type of variability has emerged in jetted AGN lightcurves, specifically, the observation of a long-term trend characterized by a linear increase of the flux with time in blazars such as PG 1553+113, which is among the objects most likely to display periodic behavior. In this paper, we present the results of a systematic search for long-term trends, spanning $\approx$10\, years, utilizing 12 years of Fermi-LAT observations. The study is focused on detecting the presence of linear or quadratic long-term trends in a sample of 3308 jetted AGN. Our analysis has identified 40 jetted AGN that exhibit long-term trends, each with distinct properties, which we also characterize in this study. These long-term trends may originate from the dynamics of a supermassive black hole binary system, or they could be the result of intrinsic phenomena within the jet itself. Our findings can help in addressing questions pertaining to the astrophysical origins of variability and periodicity within jetted AGN.