Detection of Quasiperiodic Oscillations in the Blazar S4 0954+658 with TESS

We report the detection of several quasiperiodicities around 0.6-2.5 days in the optical emission of the blazar S4 0954+658. The source was observed by the Transiting Exoplanet Survey Satellite in six sectors and it showed these features in all but one of them, with a quasiperiodic oscillation of 1.52 days apparently present in portions of four of them. We used the generalized Lomb-Scargle periodogram method to search for significant signals and we confirmed them using a weighted wavelet transform for time-frequency domain analyses. We discuss several possible explanations for these rapid quasiperiodic variations and suggest that an origin in the innermost part of the accretion disk is most likely. Within this framework, we provide estimates for the mass of the black hole at the core of this blazar.