S5 0716+714 : GeV variability study

TL;DR

This study analyzes over three years of Fermi-LAT data on the BL Lac object S5 0716+714, revealing two distinct flux variability modes, spectral hardening, and a broken power law spectrum, enhancing understanding of its high-energy emission behavior.

Contribution

It provides the first detailed characterization of the GeV variability and spectral features of S5 0716+714 over an extended period, identifying two flux variability modes and spectral break behavior.

Findings

Two flux variability modes with ~75 and ~140 days timescales

Weak spectral hardening during flux variations

Spectral break energy remains constant across activity states

Abstract

The GeV observations by Fermi-LAT give us the opportunity to characterize the high-energy emission (100 MeV - 300 GeV) variability properties of the BL Lac object S5 0716+714. In this study, we performed flux and spectral analysis of more than 3 year long (August 2008 to April 2012) Fermi-LAT data of the source. During this period, the source exhibits two different modes of flux variability with characteristic timescales of ~75 and ~140 days, respectively. We also notice that the flux variations are characterized by a weak spectral hardening. The GeV spectrum of the source shows a clear deviation from a simple power law, and is better explained by a broken power law. Similar to other bright Fermi blazars, the break energy does not vary with the source flux during the different activity states. We discuss several possible scenarios to explain the observed spectral break.