Correlation between optical and $\gamma$-ray flux variations in bright flat spectrum radio quasars

Abstract

Blazars are known to show flux variations over a range of energies from low energy radio to high energy gamma-rays. Cross-correlation analysis of the optical and $\gamma$-ray light curves in blazars shows that flux variations are generally correlated in both bands, however, there are exceptions. We explored this optical-GeV connection in four flat spectrum radio quasars (FSRQs) by a systematic investigation of their long term optical and $\gamma$-ray light curves. On analysis of the four sources, namely 3C 273, 3C 279, PKS 1510$-$089 and CTA 102 we noticed different behaviours between the optical and GeV flux variations. We found instances when (i) the optical and GeV flux variations are closely correlated (ii) there are optical flares without $\gamma$-ray counterparts and (iii) $\gamma$-ray flares without optical counterparts. To understand these diverse behaviours, we carried out broad band spectral energy distribution (SED) modelling of the sources at different epochs using a one-zone leptonic emission model. The optical-UV emission is found to be dominated by emission from the accretion disk in the sources PKS 1510$-$089, CTA 102 and 3C 273, while in 3C 279, the synchrotron radiation from the jet dominates the optical-UV emission. Our SED analysis indicates that (i) correlated optical and $\gamma$-ray flux variations are caused by changes in the bulk Lorentz factor ($\Gamma$), (ii) $\gamma$-ray flares without optical counterparts are due to increase in $\Gamma$ and/or the electron energy density and (iii) an optical flare without $\gamma$-ray counterpart is due to increase in the magnetic field strength.

22 pages, 32 figures, accepted to MNRAS

References in corpus (25)

• Very-High-Energy Gamma Rays from a Distant Quasar: How Transparent Is the Universe?
• Doppler factors, Lorentz factors and viewing angles for quasars, BL Lacertae objects and radio galaxies
• Bright AGN Source List from the First Three Months of the Fermi Large Area Telescope All-Sky Survey
• Kinematics of Parsec-Scale Jets of Gamma-Ray Blazars at 43~GHz within the VLBA-BU-BLAZAR Program
• A change in the optical polarization associated with a gamma-ray flare in the blazar 3C 279
• Modeling the Emission Processes in Blazars
• The blazar sequence: a new perspective
• GeV breaks in blazars as a result of gamma-ray absorption within the broad-line region
• Correlated Multi-Waveband Variability in the Blazar 3C~279 from 1996 to 2007
• Multi-wavelength observations of 3C 279 during the extremely bright gamma-ray flare in 2014 March-April
• Through The Ring Of Fire: $\gamma$-Ray Variability In Blazars By A Moving Plasmoid Passing A Local Source Of Seed Photons
• Temporal Correlations Between Optical and Gamma-ray Activity in Blazars
• Long term variability and correlation study of the blazar 3C 454.3 in radio, NIR and optical wavebands
• Temporal correlation between the optical and γ-ray flux variations in the blazar 3C 454.3
• Long term study of the light curve of PKS 1510-089 in GeV energies
• Gamma-ray Luminosity and Photon Index Evolution of FSRQ Blazars and Contribution to the Gamma-ray Background
• Long term γ -ray variability of blazars
• A hadronic minute-scale GeV flare from quasar 3C 279?
• Flux and polarization variability of OJ 287 during early 2016 outburst
• Optical Variability of TeV Blazars on long time-scales
• Multiband optical flux density and polarization microvariability study of optically bright blazars
• Investigation of the Gamma-ray Spectrum of CTA 102 During the Exceptional Flaring State in 2016-2017
• Modelling the $\gamma$-ray variability of 3C 273
• An Investigation into the Spectral Properties of Bright Fermi Blazars
• Constraints on jet-driven disk accretion in Sagittarius A*

Cited by in corpus (7)

• The Central Engines of Fermi Blazars
• Modeling the time variable spectral energy distribution of the blazar CTA 102 from 2008 to 2022
• Study of correlation between optical flux and polarization variations in BL Lac objects
• A numerical study of long-term multi-wavelength blazar variability
• Broadband study of OQ 334 during its flaring state
• Correlation between optical and $\gamma$-ray flux variations in BL Lacs
• Correlation between emission-line luminosity and gamma-ray dominance in the blazar 3C 279