Two Repeated Quasi-periodic Oscillations in the FSRQ S5 1044+71 Observed by TESS

Abstract In this work, we report for the first time two repeated quasi-periodic oscillations (QPOs) in the light curve of the Flat Spectrum Radio Quasar S5 1044+71. This source was observed by the Transiting Exoplanet Survey Satellite in multiple sectors. We used the generalized Lomb-Scargle periodogram method and weighted wavelet Z -transform method to search for significant periodic signals. The main results are as follows: We found QPOs of ~7.0 days (persisted for 4 cycles, with a significance of ~3.5 σ ) and ~7.3 days (persisted for 5 cycles, with a significance of ~3.8 σ ) in the light curves of Sector 47 and EP1, respectively. Considering range of error, we regard them to be the same. We discussed two likely models of these rapid quasi-periodic variations: One comes from the jet and the other from the accretion disk. For the first one, we consider kink instability of the jet as a plausible explanation. Second, the QPO probably comes from the main hot spots in the accretion disk, which are located approximately within the innermost stable circular orbit allowed by general relativity. Based on this model, we estimate the mass of the black hole in S5 1044+71 to be 3.49 × 10 9 M ⊙ .