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Correlation Analysis of Delays between Variations of Gamma-Ray and Optical Light Curves of Blazars

Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
Astronomical Institute, St. Petersburg State University, Universitetskij Pr. 28, Petrodvorets, 198504 St. Petersburg, Russia
Main (Pulkovo) Astronomical Observatory of RAS, Pulkovskoye shosse, 60, 196140 St. Petersburg, Russia
Isaac Newton Institute of Chile, St. Petersburg Branch, 198504 St. Petersburg, Russia
Instituto de Astrofísica de Andalucía, CSIC, Apartado 3004, 18080 Granada, Spain
Department of Physics, University of Crete, 71003 Heraklion, Greece
Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
Lowell Observatory, Flagstaff, AZ 86001, USA
Author to whom correspondence should be addressed.
Academic Editors: Jose L. Gómez, Alan P. Marscher and Svetlana G. Jorstad
Galaxies 2016, 4(4), 64;
Received: 14 July 2016 / Revised: 11 November 2016 / Accepted: 15 November 2016 / Published: 23 November 2016
(This article belongs to the Special Issue Blazars through Sharp Multi-wavelength Eyes)
We have been performing multi-wavelength monitoring of a sample of γ -ray blazars since the launch of the Fermi Gamma-ray Space Telescope in 2008. We present γ -ray and optical light curves for several quasars and BL Lac objects from the sample to illustrate different patterns of variability. We investigate correlations between γ -ray and R-band light curves and, if these are statistically significant, determine delays between variations at the two wavebands. Such time delays can reveal the relative locations of the emitting regions in AGN jets and the origin of the high-energy photons. We present preliminary results of this analysis. Of the 29 blazars with sufficient time coverage, 17 display a significant, singular, correlated time lag when tested over the entire 7-year period. Of these sources, the six that exhibit a consistent time lag across a majority of epochs of high activity have lags of 0 ± 7 days; the 11 without consistency across epochs of high activity generally display longer mean lags, with γ -ray leading optical. Eleven sources display no significant singular correlation over either the entire 7-year period or across shorter intervals. No significant difference is apparent between the BL Lac objects and FSRQs. Even after 7 years of monitoring, our correlation analysis remains plagued with uncertainties due to insufficient data. View Full-Text
Keywords: galaxies:active; galaxies: jets; quasars: general; BL Lacertae objects: general galaxies:active; galaxies: jets; quasars: general; BL Lacertae objects: general
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Williamson, K.E.; Jorstad, S.G.; Marscher, A.P.; Larionov, V.M.; Agudo, I.; Arkharov, A.A.; Blinov, D.A.; Casadio, C.; Gómez, J.L.; Hagen-Thorn, V.A.; Joshi, M.; Konstantinova, T.S.; Kopatskaya, E.N.; Larionova, E.G.; Larionova, L.V.; Malmrose, M.P.; McHardy, I.M.; Molina, S.N.; Morozova, D.A.; Taylor, B.W.; Troitsky, I.S. Correlation Analysis of Delays between Variations of Gamma-Ray and Optical Light Curves of Blazars. Galaxies 2016, 4, 64.

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