Abstract:
We present periodicity search analyses on the γ -ray light curve of the TeV blazar PKS 1510-089 observed by the Fermi Large
Area Telescope. We report the detection of two transient quasi-periodic oscillations: A 3.6-d QPO during the outburst in 2009 that
lasted five cycles (MJD 54906–54923); and a periodicity of 92 d spanning over 650 d from 2018 to 2020 (MJD 58200–58850),
which lasted for seven cycles. We employed the Lomb–Scargle periodogram, Weighted Wavelet Z-transform, REDFIT, and the
Monte Carlo light-curve simulation techniques to find any periodicity and the corresponding significance. The 3.6-d QPO was
detected at a moderate significance of ∼3.5σ, while the detection significance of the 92-d QPO was ∼7.0σ. We explore a
few physical models for such transient QPOs including a binary black hole system, precession of the jet, a non-axisymmetric
instability rotating around the central black hole near the innermost stable circular orbit, the presence of quasi-equidistant
magnetic islands inside the jet, and a geometric model involving a plasma blob moving helically inside a curved jet.
