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.