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Characterizing the Optical Variability of Bright Blazars: Variability-based Selection of Fermi Active Galactic Nuclei

Ruan, John J. and Anderson, Scott F. and MacLeod, Chelsea L. and Becker, Andrew C. and Burnett, T. H. and Davenport, James R. A. and Ivezić, Željko and Kochanek, Christopher S. and Plotkin, Richard M. and Sesar, Branimir and Stuart, J. Scott (2012) Characterizing the Optical Variability of Bright Blazars: Variability-based Selection of Fermi Active Galactic Nuclei. Astrophysical Journal, 760 (1). Art. No. 51. ISSN 0004-637X. doi:10.1088/0004-637X/760/1/51.

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We investigate the use of optical photometric variability to select and identify blazars in large-scale time-domain surveys, in part to aid in the identification of blazar counterparts to the ∼30% of γ -ray sources in the Fermi 2FGL catalog still lacking reliable associations. Using data from the optical LINEAR asteroid survey, we characterize the optical variability of blazars by fitting a damped random walk model to individual light curves with two main model parameters, the characteristic timescales of variability τ , and driving amplitudes on short timescales σ . Imposing cuts on minimum τ and σ allows for blazar selection with high efficiency E and completeness C. To test the efficacy of this approach, we apply this method to optically variable LINEAR objects that fall within the several arcminute error ellipses of γ -ray sources in the Fermi 2FGL catalog. Despite the extreme stellar contamination at the shallow depth of the LINEAR survey, we are able to recover previously associated optical counterparts to Fermi active galactic nuclei with E ≥ 88% and C = 88% in Fermi 95% confidence error ellipses having semimajor axis r < 8'. We find that the suggested radio counterpart to Fermi source 2FGL J1649.6+5238 has optical variability consistent with other γ -ray blazars and is likely to be the γ -ray source. Our results suggest that the variability of the non-thermal jet emission in blazars is stochastic in nature, with unique variability properties due to the effects of relativistic beaming. After correcting for beaming, we estimate that the characteristic timescale of blazar variability is ∼3 years in the rest frame of the jet, in contrast with the ∼320 day disk flux timescale observed in quasars. The variability-based selection method presented will be useful for blazar identification in time-domain optical surveys and is also a probe of jet physics.

Item Type:Article
Related URLs:
URLURL TypeDescription
Ruan, John J.0000-0001-8665-5523
Davenport, James R. A.0000-0002-0637-835X
Ivezić, Željko0000-0001-5250-2633
Kochanek, Christopher S.0000-0001-6017-2961
Plotkin, Richard M.0000-0002-7092-0326
Sesar, Branimir0000-0002-0834-3978
Additional Information:© 2012 Received 2012 August 6; accepted 2012 September 28; published 2012 November 2. The authors thank Eric Agol (University of Washington) and Ying Zu (Ohio State University) for helpful discussions regarding AGN variability. Ž.I. and C.L.M. acknowledge support by NSF grant AST-0807500 to the University of Washington, NSF grant AST-0551161 to LSST for design and development activity, and Croatian National Science Foundation grant O-1548-2009. R.M.P. acknowledges support from a Netherlands Organization for Scientific Research (NWO) Vidi Fellowship. C.S.K. is supported by NSF grant AST-1009756. B.S. acknowledges NSF grant AST-0908139 awarded to Judy Cohen for partial support. The LINEAR program is sponsored by the National Aeronautics and Space Administration (NRA No. NNH09ZDA001N, 09-NEOO09-0010) and the United States Air Force under Air Force Contract FA8721-05-C-0002. Opinions, interpretations, conclusions, and recommendations are those of the authors and are not necessarily endorsed by the United States Government.
Funding AgencyGrant Number
Croatian National Science FoundationO-1548-2009
Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO)UNSPECIFIED
Air ForceFA8721-05-C-0002
Subject Keywords:BL Lacertae objects: general; galaxies: active; quasars: general
Issue or Number:1
Record Number:CaltechAUTHORS:20121218-090528634
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Official Citation:Characterizing the Optical Variability of Bright Blazars: Variability-based Selection of Fermi Active Galactic Nuclei John J. Ruan, Scott F. Anderson, Chelsea L. MacLeod, Andrew C. Becker, T. H. Burnett, James R. A. Davenport, Željko Ivezić, Christopher S. Kochanek, Richard M. Plotkin, Branimir Sesar, and J. Scott Stuart doi:10.1088/0004-637X/760/1/51
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:36027
Deposited By: Ruth Sustaita
Deposited On:18 Dec 2012 18:21
Last Modified:09 Nov 2021 23:19

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