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Published October 21, 2015 | Published + Submitted
Journal Article Open

RoboPol: first season rotations of optical polarization plane in blazars


We present first results on polarization swings in optical emission of blazars obtained by RoboPol, a monitoring programme of an unbiased sample of gamma-ray bright blazars specially designed for effective detection of such events. A possible connection of polarization swing events with periods of high activity in gamma-rays is investigated using the data set obtained during the first season of operation. It was found that the brightest gamma-ray flares tend to be located closer in time to rotation events, which may be an indication of two separate mechanisms responsible for the rotations. Blazars with detected rotations during non-rotating periods have significantly larger amplitude and faster variations of polarization angle than blazars without rotations. Our simulations show that the full set of observed rotations is not a likely outcome (probability ≤1.5 × 10^(−2)) of a random walk of the polarization vector simulated by a multicell model. Furthermore, it is highly unlikely (∼5 × 10^(−5)) that none of our rotations is physically connected with an increase in gamma-ray activity.

Additional Information

© 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 July 27. Received 2015 July 27; in original form 2015 May 28. First published online August 26, 2015. The RoboPol project is a collaboration between Caltech in the USA, MPIfR in Germany, Toruń Centre for Astronomy in Poland, the University of Crete/FORTH in Greece and IUCAA in India. The University of Crete group acknowledges support by the 'RoboPol' project, which is implemented under the 'Aristeia' Action of the 'Operational Programme Education and Lifelong Learning' and is co-funded by the European Social Fund (ESF) and Greek National Resources, and by the European Commission Seventh Framework Programme (FP7) through grants PCIG10-GA-2011-304001 'JetPop' and PIRSES-GA-2012-31578 'EuroCal'. This research was supported in part by NASA grant NNX11A043G and NSF grant AST-1109911, and by the Polish National Science Centre, grant number 2011/01/B/ST9/04618. KT acknowledges support by the FP7 through the Marie Curie Career Integration Grant PCIG-GA-2011-293531 'SFOnset'. MB acknowledges support from NASA Headquarters under the NASA Earth and Space Science Fellowship Program, grant NNX14AQ07H. TH was supported in part by the Academy of Finland project number 267324. IM and SK are supported for this research through a stipend from the International Max Planck Research School (IMPRS) for Astronomy and Astrophysics at the Universities of Bonn and Cologne. 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 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, Istituto Nazionale di Astrofisica in Italy and the Centre National d'Études Spatiales in France.

Attached Files

Published - MNRAS-2015-Blinov-1669-83.pdf

Submitted - 1505.07467.pdf


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