Periodicity in the continua and broad line curves of a quasar E1821+643

Understand

Here we present an in-depth analysis of the periodicity of the continua and broad emission lines of a quasar E1821+643.

• We applied non-parametric composite models, the linear sum of stationary and non-stationary Gaussian processes, and quantified contribution of their periodic parts.
• We found important qualitative differences among the three periodic signals.
• Periods of $\sim 2200$ and $\sim 4500$ days appear in both continua 5100 \AA \, and 4200 \AA \,, as well as in the H$\gamma$ emission line.