On the location of the γ-ray outburst emission in the BL Lacertae object AO 0235+164 through observations across the electromagnetic spectrum

Iván Agudo, Alan P. Marscher, Svetlana G. Jorstad, Valeri M. Larionov, José L. Gómez, Anne Lähteenmäki, Paul S. Smith, Kari Nilsson, Anthony C.S. Readhead, Margo F. Aller, Jochen Heidt, Mark Gurwell, Clemens Thum, Ann E. Wehrle, Maria G. Nikolashvili, Hugh D. Aller, Erika Benítez, Dmitriy A. Blinov, Vladimir A. Hagen-Thorn, David HiriartBuell T. Jannuzi, Manasvita Joshi, Givi N. Kimeridze, Omar M. Kurtanidze, Sofia O. Kurtanidze, Elina Lindfors, Sol N. Molina, Daria A. Morozova, Elina Nieppola, Alice R. Olmstead, Riho Reinthal, Mar Roca-Sogorb, Gary D. Schmidt, Lorand A. Sigua, Aimo Sillanpää, Leo Takalo, Brian Taylor, Merja Tornikoski, Ivan S. Troitsky, Alma C. Zook, Helmut Wiesemeyer

Research output: Contribution to journalArticlepeer-review

109 Scopus citations


We present observations of a major outburst at centimeter, millimeter, optical, X-ray, and γ-ray wavelengths of the BL Lacertae object AO 0235+164. We analyze the timing of multi-waveband variations in the flux and linear polarization, as well as changes in Very Long Baseline Array images at λ = 7mm with 0.15 milliarcsec resolution. The association of the events at different wavebands is confirmed at high statistical significance by probability arguments and Monte Carlo simulations. A series of sharp peaks in optical linear polarization, as well as a pronounced maximum in the 7 mm polarization of a superluminal jet knot, indicate rapid fluctuations in the degree of ordering of the magnetic field. These results lead us to conclude that the outburst occurred in the jet both in the quasi-stationary "core" and in the superluminal knot, both parsecs downstream of the supermassive black hole. We interpret the outburst as a consequence of the propagation of a disturbance, elongated along the line of sight by light-travel time delays, that passes through a standing recollimation shock in the core and propagates down the jet to create the superluminal knot. The multi-wavelength light curves vary together on long timescales (months/years), but the correspondence is poorer on shorter timescales. This, as well as the variability of the polarization and the dual location of the outburst, agrees with the expectations of a multi-zone emission model in which turbulence plays a major role in modulating the synchrotron and inverse Compton fluxes.

Original languageEnglish (US)
Article numberL10
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Jul 1 2011


  • BL Lacertae objects: individual (AO 0235+164)
  • 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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