Reversals in the Direction of Polarization Rotation in OJ 287
We have obtained a smooth time series for the electric vector position angle (EVPA) of the blazar OJ 287 at centimeter wavelengths, by making ±nπ adjustments to archival values from 1974 to 2016. The data display rotation reversals in which the EVPA rotates counterclockwise for ~180° and then rotates clockwise by a similar amount. The timescale of the rotations is a few weeks to a year, and the scale for a double rotation, including the reversal, is 1–3 yr. We have seen four of these events in 40 yr. A model consisting of two successive outbursts in polarized flux density, with EVPAs counterrotating, superposed on a steady polarized jet, can explain many of the details of the observations. Polarization images support this interpretation. The model can also help to explain similar events seen at optical wavelengths. The outbursts needed for the model can be generated by the supermagnetosonic jet model of Nakamura et al. and Nakamura & Meier, which requires a strong helical magnetic field. This model produces forward and reverse pairs of fast and slow MHD waves, and the plasma inside the two fast/slow pairs rotates around the jet axis, but in opposite directions.
Additional Information© 2018 The American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2018 January 29; revised 2018 June 2; accepted 2018 June 5; published 2018 July 17. We thank the referee, D. C. Gabuzda, for a thorough reading of the manuscript and for many suggestions that improved the paper. We are grateful to D. E. Homan and S. Kiehlmann for reading the manuscript and making useful suggestions, and to the entire MOJAVE team for their years of work in assembling the data used here. This research has made use of data from the MOJAVE database that is maintained by the MOJAVE team (Lister et al. 2009); the MOJAVE program is supported under NASA-Fermi grant NNX15AU76G. Operations at UMRAO were supported by the University of Michigan, and research there was funded in part by NASA-Fermi GI grants NNX09AU16G, NNX10AP16G, NNX11AO13G, and NNX13AP18G and NSF grant AST-0607523. Y.Y.K. and A.B.P. were supported by the Russian Foundation for Basic Research (project 17-02-00197), the Basic Research Program P-28 of the Presidium of the Russian Academy of Sciences, and the government of the Russian Federation (agreement 05.Y09.21.0018). T.S. was funded by the Academy of Finland projects 274477 and 284495. This research has been supported in part by the Alexander von Humboldt Foundation, and it has made use of the Swinburne University of Technology software correlator, developed as part of the Australian Major National Research Facilities Programme and operated under license (Deller et al. 2007).
Published - Cohen_2018_ApJ_862_1.pdf
Accepted Version - 1806.02870.pdf