Gamma-ray and optical oscillations in the blazar PKS 0537-441

TL;DR

This study identifies a ~280-day gamma-ray and optical oscillation in the blazar PKS 0537-441 during a high emission state, suggesting some blazars exhibit month-year periodicities linked to active phases.

Contribution

The paper reports the detection of a significant ~280-day oscillation in gamma-ray and optical light curves of PKS 0537-441 during a high state, highlighting phase-dependent periodicities in blazars.

Findings

A ~280-day period in gamma-ray light curve with 99.7% significance.

Optical light curves show a similar period during high emission phases.

Month-year oscillations may be characteristic of certain blazars during active states.

Abstract

We have considered the \textit{Fermi} $\gamma$-ray light curve of the blazar PKS 0537-441 during a high state extending from 2008/08/10 to 2011/08/27. The periodogram exhibits a peak at T $\sim$ 280 d, with a significance of $\sim$ 99.7 \%. A peak of similar relevance at $\frac{1}{2}$ T is found in the optical light curves. Considering the entire duration of the \textit{ Fermi} light curve 2008-2015, no significant peak is revealed, while the optical one remains meaningful. Comparing with recent observations of PKS 2155-304 and PG 1553+113 it seems that month-year oscillations can characterize some blazars. Month-scale oscillations can also show up only during phases of enhanced or bursting emission like in the case of PKS 0537-441.