RoboPol: optical polarization-plane rotations and flaring activity in blazars
We present measurements of rotations of the optical polarization of blazars during the second year of operation of RoboPol, a monitoring programme of an unbiased sample of gamma-ray bright blazars specially designed for effective detection of such events, and we analyse the large set of rotation events discovered in two years of observation. We investigate patterns of variability in the polarization parameters and total flux density during the rotation events and compare them to the behaviour in a non-rotating state. We have searched for possible correlations between average parameters of the polarization-plane rotations and average parameters of polarization, with the following results: (1) there is no statistical association of the rotations with contemporaneous optical flares; (2) the average fractional polarization during the rotations tends to be lower than that in a non-rotating state; (3) the average fractional polarization during rotations is correlated with the rotation rate of the polarization plane in the jet rest frame; (4) it is likely that distributions of amplitudes and durations of the rotations have physical upper bounds, so arbitrarily long rotations are not realized in nature.
Additional Information© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2016 January 15. Received 2016 January 13. In original form 2015 December 3. First published online February 10, 2016. The RoboPol project is a collaboration between the University of Crete/FORTH in Greece, Caltech in the USA, MPIfR in Germany, IUCAA in India and Toruń Centre for Astronomy in Poland. The U. 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 Comission 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. DB acknowledges support from the St. Petersburg University research grant 6.38.335.2015. KT acknowledges support by the European Commission Seventh Framework Programme (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 NNX14AQ07. HTH was supported 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.
Published - Blinov,Detal.pdf
Submitted - 1601.03392v2.pdf