Spectroscopic Monitoring of Blazar S5 0716+714: Brightness-Dependent Spectral Behavior

Abstract

In this paper, we report the new results of spectroscopic observations of $\gamma$-ray blazar S5 0716+714 from 2019 September to 2020 March with the 2.4 m optical telescope at Lijiang Observatory of Yunnan Observatories. The median cadence of observations is $\sim$ 1 day. During the second observation period (Epoch2), the observational data reveal an extremely bright state and a bluer-when-brighter (BWB) chromatism. The BWB trend of Epoch2 differs significantly from that of the first observation period (Epoch1). A significantly brightness-dependent BWB chromatism emerges in the total data of Epoch1 and Epoch2. The BWB trend becomes weaker towards the brighter states, and likely becomes saturated at the highest state. Based on a log-parabolic function, a power-law of synchrotron peak flux and frequency ${\nu }_{\mathrm{p}}$, and a power-law of the curvature of synchrotron spectrum and its ${\nu }_{\mathrm{p}}$, simulation well reproduces the brightness-dependent BWB trend of S5 0716+714. The BWB trend is seemingly controlled by the shift of ${\nu }_{\mathrm{p}}$ with respect to the observational window, and effectively may be dominated by the variations of electron average energy and magnetic field in emitting region.

16 pages, 5 figures, Accepted for publication in ApJ

References in corpus (6)

• The Spectral Energy Distributions of Fermi Blazars
• Fermi/LAT broad emission line blazars
• X-ray spectral evolution of TeV BL Lac objects: eleven years of observations with BeppoSAX, XMM-Newton and SWIFT satellites
• Signatures of synchrotron emission and of electron acceleration in the X-ray spectra of Mrk 421
• The curvature of spectral energy distribution of blazars
• On the Origin and Evolution of Curvature of the Spectral Energy Distribution of Fermi Bright Blazars

Cited by in corpus (4)

• Multi-wavelength Variation Phenomena of PKS 0735+178 on Diverse Timescale
• Long-term multiband optical variability of S5 0716+714 blazar
• Multi-wavelength variability analysis of the blazar S5 0716+714 during a long-lasting period of low activity
• Optical Monitoring and Long-term Optical Spectral Variability of BL Lacertae Object S5 0716+714