Periodicity Analysis of Mrk 501 and Mrk 421 in Gamma Rays

Blazars, a subclass of active galactic nuclei (AGNs), are highly variable objects. Quasiperiodic oscillations (QPOs), which might originate from a binary black hole located at the AGN core, have been found in some blazar light curves. For the blazars Mrk 421 and Mrk 501, we test the possible QPO behavior using a variety of methods (generalized Lomb-Scargle periodogram, continuous-time autoregressive moving average models, wavelet scalograms, and A - T plane), studying systematic effects in detail. We use gamma-ray light curves from FACT, a ground-based imaging air Cherenkov telescope. We report herein on a 3 sigma-significant QPO in Mrk 421.