Multiwavelength Analysis of Fermi-LAT Blazars with High-Significance Periodicity: Detection of a Long-Term Rising Emission in PG 1553+113

TL;DR

This study analyzes multiwavelength data of five blazars with gamma-ray periodicity, revealing correlated emission across bands and a long-term rising trend in PG 1553+113, providing insights into their emission mechanisms and possible binary black hole systems.

Contribution

It presents the first multiwavelength analysis of blazars with gamma-ray periodicity, identifying correlated emission and a long-term trend in PG 1553+113, advancing understanding of their variability.

Findings

Detection of similar periodic patterns in optical and radio bands for three blazars.

Correlation of fluxes across different electromagnetic bands, indicating co-spatial emission regions.

Observation of a long-term rising trend in PG 1553+113's light curve, constraining binary black hole models.

Abstract

Blazars display variable emission across the entire electromagnetic spectrum, with timescales that can range from a few minutes to several years. Our recent work has shown that a sample of five blazars exhibit hints of periodicity with a global significance $\gtrsim2\,\sigma$ at $\gamma$-ray energies, in the range of 0.1~GeV$<$E$<$800~GeV. In this work, we study their multiwavelength (MWL) emission, covering the X-ray, ultraviolet, optical, and radio bands. We show that three of these blazars present similar periodic patterns in the optical and radio bands. Additionally, fluxes in the different bands of the five blazars are correlated, suggesting a co-spatial origin. Moreover, we detect a long-term ($\approx$10 year) rising trend in the light curves of PG~1553+113, and we use it to infer possible constraints on the binary black hole hypothesis.