Abstract
Abstract We present the results of an extensive γ-ray data analysis of the emission from the blazar S5 0716+714 with the primary motivation to study its temporal and spectral variability behavior. In this work, we extract a 10 days binned γ-ray light curve from 2008 August 4 to 2016 April 27 in the energy range of 0.1–300 GeV and identify six outburst periods with peak flux of >4 × 10−7 ph cm−2 s−1 from this highly variable source. The brightest flares are identified by zooming in these outburst periods to 1 day binning and using the Bayesian Blocks algorithm. The fastest variability timescale is found to be 1.5 ± 0.3 hr at MJD 57128.01 ± 0.01 with a peak flux above 100 MeV of (26.8 ± 6.9) × 10−7 ph cm−2 s−1. No hint of periodic modulations has been detected for the light curve of S5 0716+714. During the outburst phases, the γ-ray spectrum shows an obvious spectral break with a break energy between 0.93 and 6.90 GeV energies, which may be caused by an intrinsic break in the energy distribution of radiating particles. The five highest-energy photons, with E > 100 GeV, imply that the high-energy emission from this source may originate from a moving emission region in a helical path upstream in the jet. The spectral behavior and temporal characteristics of the individual flares indicate that the location of the emission region lies in the sub-parsec scale (r γ < 0.85 pc).
Highlights
Blazars, including BL Lac objects and flat-spectrum radio quasars, whose relativistic jets are pointed close to our line of sight, represent a small subclass of active galactic nuclei (AGNs), which are extremely variable objects in the sky (e.g., Blandford & Königl 1979; Urry & Padovani 1995)
We presented a detailed investigation of the γ-ray flux and spectral variations of the blazar S5 0716+714 for 8 years of Fermi-Large Area Telescope (LAT) observations, from 2008 August 4 to 2016 April 27
The source displays significant flaring activity after 2011, with six major outburst phases and many substructures found in the 10 days binned light curve
Summary
Blazars, including BL Lac objects and flat-spectrum radio quasars, whose relativistic jets are pointed close to our line of sight, represent a small subclass of active galactic nuclei (AGNs), which are extremely variable objects in the sky (e.g., Blandford & Königl 1979; Urry & Padovani 1995). No emission or absorption lines were identified in this source, and it is highly variable from radio to γ-ray energies (Wagner et al 1996). Danforth et al (2013) set a statistical upper bound of z < 0.32 with a 95% confidence for this source by using Hubble Space Telescope observations This source is classified as an intermediate-synchrotron-peaked blazar The γ-ray properties of some blazars have been studied with minute-scale and hour/sub-hour scale γ-ray variability (see, e.g., Aleksić et al 2011; Ackermann et al 2016; Prince et al 2017; Shukla et al 2018; Ding et al 2019) These studies implied that the short-timescale γ-ray variability may be produced in a compact high-energy emission region located far away from the black hole, at the edge or outside of the BLR.
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