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Open AccessArticle

Fractional Variability—A Tool to Study Blazar Variability

Institute for Theoretical Physics and Astrophysics, Universität Würzburg, 97070 Würzburg, Germany
Institute for Particle Physics and Astrophysics, ETH Zurich, 8093 Zurich, Switzerland
Experimental Physics 5, TU Dortmund, 44227 Dortmund, Germany
ISDC Data Center for Astrophysics, University of Geneva, 1205 Geneva, Switzerland
Authors to whom correspondence should be addressed.
Also at RWTH Aachen University.
Galaxies 2019, 7(2), 62;
Received: 8 February 2019 / Revised: 17 May 2019 / Accepted: 23 May 2019 / Published: 30 May 2019
(This article belongs to the Special Issue Monitoring the Non-Thermal Universe)
PDF [1944 KB, uploaded 31 May 2019]


Active Galactic Nuclei emit radiation over the whole electromagnetic spectrum up to TeV energies. Blazars are one subtype with their jets pointing towards the observer. One of their typical features is extreme variability on timescales, from minutes to years. The fractional variability is an often used parameter for investigating the degree of variability of a light curve. Different detection methods and sensitivities of the instruments result in differently binned data and light curves with gaps. As they can influence the physics interpretation of the broadband variability, the effects of these differences on the fractional variability need to be studied. In this paper, we study the systematic effects of completeness in time coverage and the sampling rate. Using public data from instruments monitoring blazars in various energy ranges, we study the variability of the bright TeV blazars Mrk 421 and Mrk 501 over the electromagnetic spectrum, taking into account the systematic effects, and compare our findings with previous results. Especially in the TeV range, the fractional variability is higher than in previous studies, which can be explained by the much longer (seven years compared to few weeks) and more complete data sample. View Full-Text
Keywords: blazars; variability; fractional variability; active galactic nuclei blazars; variability; fractional variability; active galactic nuclei

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Schleicher, B.; Arbet-Engels, A.; Baack, D.; Balbo, M.; Biland, A.; Blank, M.; Bretz, T.; Bruegge, K.; Bulinski, M.; Buss, J.; Doerr, M.; Dorner, D.; Elsaesser, D.; Grischagin, S.; Hildebrand, D.; Linhoff, L.; Mannheim, K.; Mueller, S.A.; Neise, D.; Neronov, A.; Noethe, M.; Paravac, A.; Rhode, W.; Schulz, F.; Sedlaczek, K.; Shukla, A.; Sliusar, V.; Willert, E.V.; Walter, R. Fractional Variability—A Tool to Study Blazar Variability. Galaxies 2019, 7, 62.

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