Quasi-periodic Oscillation and Evidence of a Curved Jet in the Blazar 3C 454.3

Arkadipta Sarkar, Alok C. Gupta, Varsha R. Chitnis, Paul J. Wiita

Published 2020-03-04Version 1

We report the detection of a quasi-periodic oscillation (QPO) in light curves of the blazar 3C 454.3. Periodic flux modulation was detected simultaneously in both $\gamma$--ray and optical wavebands with a dominant period of $\sim 47$ days. This period has a significance of over $4.2\sigma$ in the \textit{Fermi} $\gamma$--ray waveband and around $2.4\sigma$ in the optical V band. This QPO lasted for over 450 days (from MJD 56800 to 57250) resulting in over nine observed periods which is among the highest number of periods ever detected in a blazar light curve. The lower significance of the dominant period in optical wavebands is attributed to the absence of optical data for a number of QPO cycles due to the daytime transit of the source. We explore several physical models to explain the origin of this transient quasi-periodic modulation in the observed flux with a month-like period. These scenarios include a binary black hole system, a hotspot orbiting close to the innermost stable circular orbit of the supermassive black hole, and precessing jets. We conclude that the most likely scenario involves a region of enhanced emission moving helically inside a jet. Also, a curvature of $\sim 0.05^{\circ}$ pc$^{-1}$ in the jet fits the emission much better than does a straight blazar jet.