2026/03/31 by Sikandar Akbar, Zahir Shah, Athar A. Dar +1
#astro-ph.HE
We present a timing analysis of the high-cadence optical light curve of the high-redshift flat-spectrum radio quasar PKS 0805-07 obtained during TESS Sector~34 (MJD~=~59230.90--59239.90). We search for short-timescale quasi-periodic oscillations (QPOs) using complementary time-series techniques, including the Lomb--Scargle periodogram (LSP) and the weighted wavelet Z-transform (WWZ), and evaluate their significance against red-noise variability using Monte Carlo simulations. The LSP reveals a dominant modulation at f ≈ 0.6 \mathrmd-1 (P ≈ 1.7 d) exceeding the 99.99% confidence level, while the WWZ independently recovers a consistent timescale at the ∼99.9% level and shows that the signal is temporally localized rather than persistent. The modulation spans ∼5 coherent cycles, indicating a transient feature. However, the significance only marginally exceeds the highest WWZ confidence threshold, and the limited number of cycles is insufficient for a firm confirmation. In a disk-based scenario, orbital motion of a hotspot near the innermost stable circular orbit implies a black hole mass of M\rm BH ∼ 7.2 × 108 M_\odot, consistent with typical FSRQ values. Alternatively, magnetohydrodynamic kink instabilities in the relativistic jet can naturally produce day-scale variability for standard blazar parameters and account for its transient character. Compact SMBH binary and tidal disruption event scenarios are disfavoured by the jet-dominated nature of the source, the optical rather than X-ray character of the modulation, and a black hole mass well above that of confirmed QPE hosts. The candidate modulation is consistent with a compact, short-lived structure embedded within stochastic jet variability, and high-cadence multiwavelength monitoring will be essential to confirm its recurrence and constrain its physical origin.