Periodic Oscillations in the Intra-day Optical Light Curves of the Blazar S5 0716+714

TL;DR

This study identifies strong quasi-periodic oscillations in the optical light curves of blazar S5 0716+714, providing evidence for accretion disk-related variability and estimating the black hole's mass.

Contribution

First evidence of quasi-periodic components in optical intra-day variability of a blazar, using wavelet analysis and randomization tests.

Findings

Detected nearly periodic variations in 8 out of 20 light curves.

Estimated the black hole mass to be greater than 2.5 million solar masses.

Found no correlation between flux levels and variability time scales.

Abstract

We present results of a periodicity search of 20 intra-day variable optical light curves of the blazar S5 0716+714, selected from a database of 102 light curves spanning over three years. We use a wavelet analysis technique along with a randomization test and find strong candidates for nearly periodic variations in eight light curves, with probabilities ranging from 95% to >99%. This is the first good evidence for periodic, or more-precisely, quasi-periodic, components in the optical intra-day variable light curves of any blazar. Such periodic flux changes support the idea that some active galactic nuclei variability, even in blazars, is based on accretion disk fluctuations or oscillations. These intra-day variability time scales are used to estimate that the central black hole of the blazar S5 0716+714 has a mass > 2.5 \times 10^6$ M$_{\odot}$. As we did not find any correlations between the flux levels and intra-day variability time scales, it appears that more than one emission mechanism is at work in this blazar.