Multiband optical flux density and polarization microvariability study of optically bright blazars

Abstract

We present the results of flux density, spectral index, and polarization intra-night monitoring studies of a sample of eight optically bright blazars, carried out by employing several small to moderate aperture (0.4\,m to 1.5\,m diameter) telescopes fitted with CCDs and polarimeters located in Europe, India, and Japan. The duty cycle of flux variability for the targets is found to be $\sim 45$ percent, similar to that reported in earlier studies. The computed two-point spectral indices are found to be between 0.65 to 1.87 for our sample, comprised of low- and intermediate frequency peaked blazars, with one exception; they are also found to be statistically variable for about half the instances where `confirmed' variability is detected in flux density. In the analysis of the spectral evolution of the targets on hourly timescale, a counter-clockwise loop (soft-lagging) is noted in the flux-spectral index plane on two occasions, and in one case a clear spectral flattening with the decreasing flux is observed. In our data set, we also observe a variety of flux-polarization degree variability patterns, including instances with a relatively straightforward anti-correlation, correlation, or counter-clockwise looping. These changes are typically reflected in the flux-polarization angle plane: the anti-correlation between the flux and polarization degree is accompanied by an anti-correlation between the polarization angle and flux, while the counter-clockwise flux-PD looping behaviour is accompanied by a clockwise looping in the flux-polarization angle representation. We discuss our findings in the framework of the internal shock scenario for blazar sources.

MNRAS accepted

References in corpus (24)

• Active Galactic Nuclei: what's in a name?
• Kinematics of Parsec-Scale Jets of Gamma-Ray Blazars at 43~GHz within the VLBA-BU-BLAZAR Program
• Relativistic Jets Shine through Shocks or Magnetic Reconnection?
• CGRaBS: An All-Sky Survey of Gamma-Ray Blazar Candidates
• Implications of very rapid TeV variability in blazars
• Multi-colour optical monitoring of eight red blazars
• Multiwaveband Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Correlated Polarization Behavior
• Results of WEBT, VLBA and RXTE monitoring of 3C 279 during 2006-2007
• RoboPol: The optical polarization of gamma-ray--loud and gamma-ray--quiet blazars
• Detection of Possible Quasi-periodic Oscillations in the Long-term Optical Light Curve of the BL Lac Object OJ 287
• The Outburst of the Blazar AO 0235+164 in 2006 December: Shock-in-Jet Interpretation
• Longterm Optical Monitoring of Bright BL Lacertae Objects with ATOM: Spectral Variability and Multiwavelength Correlations
• Extremely violent optical microvariability in blazars: fact or fiction?
• On the reliability of microvariability tests in quasars
• The RINGO2 and DIPOL Optical Polarisation Catalogue of Blazars
• A Consolidated Framework of the Color Variability in Blazars: Long-Term Optical/Near-Infrared Observations of 3C 279
• A peculiar multi-wavelength flare in the Blazar 3C 454.3
• Short Timescale Photometric and Polarimetric Behavior of two BL Lacertae Type Objects
• Intraday Optical Variability of BL Lacertae
• Optical Variability of TeV Blazars on long time-scales
• Dense optical and near-infrared monitoring of CTA 102 during high state in 2012 with OISTER: Detection of intra-night "orphan polarized flux flare"
• Violent intra-night optical variability of the blazar S4 0954+65 during its unprecedented 2015 February outburst
• Multi-Band Intra-Night Optical Variability of BL Lacertae
• The diversity of AGN variability: Some highlights and challenges

Cited by in corpus (1)

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