Quasi-periodicities at year-like timescales in Blazars

TL;DR

This study investigates year-like quasi-periodicities in blazar light curves across optical, infrared, and gamma-ray bands, revealing frequent occurrences and exploring potential physical mechanisms behind these variabilities.

Contribution

It provides the first systematic search for year-scale quasi-periodicities in multiple blazars across different wavelengths, highlighting their commonality and discussing possible physical origins.

Findings

Year-like quasi-periodicities are common in blazar light curves.

Optical, infrared, and gamma-ray data often show correlated periodic peaks.

The significance of these peaks is evaluated considering frequency-dependent noise.

Abstract

We searched for quasi-periodicities on year-like timescales in the light curves of 6 blazars in the optical - near infrared bands and we made a comparison with the high energy emission. We obtained optical/NIR light curves from REM photometry plus archival SMARTS data and we accessed the Fermi light curves for the $\gamma$-ray data. The periodograms often show strong peaks in the optical and gamma-ray bands, which in some cases may be inter-related. The significance of the revealed peaks is then discussed, taking into account that the noise is frequency dependent. Quasi-periodicities on a year-like timescale appear to occur often in blazars. No straightforward model describing these possible periodicities is yet available, but some plausible interpretations for the physical mechanisms causing periodic variabilities of these sources are examined.