A near magnetic-to-kinetic energy equipartition flare from the relativistic jet in AO 0235 + 164 during 2013–2019

Whee Yeon Cheong, Sang Sung Lee*, Sang Hyun Kim, Sincheol Kang, Jae Young Kim, Bindu Rani, Anthony C.S. Readhead, Sebastian Kiehlmann, Anne Lähteenmäki, Merja Tornikoski, Joni Tammi, Venkatessh Ramakrishnan, Iván Agudo, Antonio Fuentes, Efthalia Traianou, Juan Escudero, Clemens Thum, Ioannis Myserlis, Carolina Casadio, Mark Gurwell

*Corresponding author for this work

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We present the multiwavelength flaring activity of the blazar AO 0235 + 164 during its recent active period from 2013 to 2019. From a discrete correlation function analysis, we find a significant (> 95 per cent) correlation between radio and gamma-ray light curves with flares at longer wavelengths following flares at shorter wavelengths. We identify a new jet component in 43 GHz Very Long Baseline Array data that was ejected from the radio core on MJD 57246+−3026 (2015 August 12), during the peak of the 2015 radio flare. From the analysis of the jet component, we derived a Doppler factor of δvar = 28.5 ± 8.4, a bulk Lorentz factor of Γ = 16.8+−33.16, and an intrinsic viewing angle of θv = 1.42+−01.5207 degrees. Investigation of the quasi-simultaneous radio data revealed a partially absorbed spectrum with the turnover frequency varying in the range of 10−70 GHz and the peak flux density varying in the range of 0.7−4 Jy. We find the synchrotron self-absorption magnetic field strength to be BSSA = 15.3+−1412.06 mG at the peak of the 2015 radio flare, which is comparable to the equipartition magnetic field strength of BEQ = 43.6+−1010.46 mG calculated for the same epoch. Additional analysis of the radio emission region in the relativistic jet of AO 0235 + 164 suggests that it did not significantly deviate from equipartition during its recent flaring activity.

Original languageEnglish
Pages (from-to)882-894
Number of pages13
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date25 Oct 2023
Publication statusPublished - 1 Jan 2024
MoE publication typeA1 Journal article-refereed


  • BL Lacertae objects: individual: AO 0235 + 164
  • galaxies: active
  • galaxies: jets
  • gamma-rays: galaxies
  • radio continuum: galaxies


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