Multiwavelength cross-correlations and flaring activity in bright blazars

Creators: Liodakis, I.; Romani, R. W.; Filippenko, A. V.; Kiehlmann, S.; Max-Moerbeck, W.; Readhead, A. C. S.; Zheng, W.

Abstract

Blazars are known for their energetic multiwavelength flares from radio wavelengths to high-energy γ-rays. In this work, we study radio, optical, and γ-ray light curves of 145 bright blazars spanning up to 8 yr, to probe the flaring activity and interband correlations. Of these, 105 show >1σ correlations between one or more wavebands, 26 of which have a >3σ correlation in at least one wavelength pair, as measured by the discrete correlation function. The most common and strongest correlations are found between the optical and γ-ray bands, with fluctuations simultaneous within our ∼30 d resolution. The radio response is usually substantially delayed with respect to the other wavelengths with median time lags of ∼100–160 d. A systematic flare identification via Bayesian block analysis provides us with a first uniform sample of flares in the three bands, allowing us to characterize the relative rates of multiband and 'orphan' flares. Multiband flares tend to have higher amplitudes than 'orphan' flares.

Additional Information

© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model) Accepted 2018 August 15. Received 2018 August 15; in original form 2018 May 17. We thank the anonymous referee and T. Hovatta for comments and suggestion that helped improve this work. The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration (NASA) and the Department of Energy in the United States, the Commissariat à l'Energie Atomique and the Centre National de la Recherche Scientifique/Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), High Energy Accelerator Research Organization (KEK), and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council, and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d'Études Spatiales in France. This research has made use of data from the robotic 0.76-m Katzman Automatic Imaging telescope (Li et al. 2003) at Lick Observatory. We thank the late Weidong Li for setting up the KAIT blazar monitoring program. This work was financed in part by NASA grants NNX10AU09G, GO-31089, NNX12AF12G, and NAS5-00147. AVF and WZ are also grateful for support from the Christopher R. Redlich Fund, the TABASGO Foundation, NSF grant AST-1211916, and the Miller Institute for Basic Research in Science (UC Berkeley). KAIT and its ongoing operation were made possible by donations from Sun Microsystems, Inc., the Hewlett-Packard Company, AutoScope Corporation, Lick Observatory, the NSF, the University of California, the Sylvia and Jim Katzman Foundation, and the TABASGO Foundation. Research at Lick Observatory is partially supported by a generous gift from Google. This work has made use of data from the OVRO 40-m monitoring program (Richards et al. 2011), which is supported in part by NASA grants NNX08AW31G, NNX11A043G, and NNX14AQ89G, as well as by NSF grants AST-0808050 and AST-1109911. AVF's research was conducted in part at the Aspen Center for Physics, which is supported by NSF grant PHY-1607611. He thanks the Centre for its hospitality during the supermassive black holes workshop in 2018 June and July.

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