Probable quasi-periodic oscillations in the TESS observations of blazars in the Swift X-ray Survey

ABSTRACT This work presents possible quasi-periodic oscillations (QPOs) in the Transiting Exoplanet Survey Satellite observations of blazars that are in the 157-month hard X-ray survey done by Swift’s Burst Alert Telescope. We report observations from four sources, J1104.4+3812, J1654.0+3946, J0353.4−6830, and J1941.3−6216, that show at least 3$\sigma$ local significance in generalized Lomb–Scargle periodogram and weighted wavelet Z-transform methods. These results are also checked using a continuous autoregressive moving average analysis that also predicts the absent data tentatively using stochastic differential equations. Each of these four sources exhibits a nominal QPO signal frequency in the range of 0.5–1.1 d$^{-1}$, resulting in at least five putative cycles. However, when the number of frequencies examined and the number of sources examined are both taken into account, the global significances are reduced to $\approx 2.2\sigma$ for J1654.0+3964 (Mrk 501), and to $\approx 1.9\sigma$ for other sources. These QPOs are thought to arise from the processes within the relativistic jet. Plausible explanations include the kink instability, which arises due to current-driven instabilities in the plasma or the precession of substructures, or mini-jets, within the jets.