Location of γ-ray flare emission in the jet of the BL Lacertae object OJ287 more than 14 pc from the central engine

Iván Agudo, Svetlana G. Jorstad, Alan P. Marscher, Valeri M. Larionov, José L. Gómez, Anne Lähteenmäki, Mark Gurwell, Paul S. Smith, Helmut Wiesemeyer, Clemens Thum, Jochen Heidt, Dmitriy A. Blinov, Francesca D. D'Arcangelo, Vladimir A. Hagen-Thorn, Daria A. Morozova, Elina Nieppola, Mar Roca-Sogorb, Gary D. Schmidt, Brian Taylor, Merja TornikoskiIvan S. Troitsky

Research output: Contribution to journalArticlepeer-review

175 Scopus citations


We combine time-dependent multi-waveband flux and linear polarization observations with submilliarcsecond-scale polarimetric images at Λ = 7 mm of the BL Lacertae type blazar OJ287 to locate the γ-ray emission in prominent flares in the jet of the source > 14 pc from the central engine. We demonstrate a highly significant correlation between the strongest γ-ray and millimeter-wave flares through Monte Carlo simulations. The two reported γ-ray peaks occurred near the beginning of two major millimeter-wave outbursts, each of which is associated with a linear polarization maximum at millimeter wavelengths. Our very long baseline array observations indicate that the two millimeter-wave flares originated in the second of two features in the jet that are separated by > 14 pc. The simultaneity of the peak of the higher-amplitude γ-ray flare and the maximum in polarization of the second jet feature implies that the γ-ray and millimeter-wave flares are cospatial and occur > 14 pc from the central engine. We also associate two optical flares, accompanied by sharp polarization peaks, with the two γ-ray events. The multi-waveband behavior is most easily explained if the γ-rays arise from synchrotron self-Compton scattering of optical photons from the flares. We propose that flares are triggered by interaction of moving plasma blobs with a standing shock. The γ-ray and optical emission is quenched by inverse Compton losses as synchrotron photons from the newly shocked plasma cross the emission region. The millimeter-wave polarization is high at the onset of a flare, but decreases as the electrons emitting at these wavelengths penetrate less polarized regions.

Original languageEnglish (US)
JournalAstrophysical Journal Letters
Issue number1 PART II
StatePublished - Jan 1 2011


  • BL Lacertae objects: individual (OJ287)
  • Galaxies: active
  • Galaxies: jets
  • Gamma rays: general
  • Polarization
  • Radio continuum: galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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