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

Abstract

<p>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_-30⁺²⁶ (2015 August 12), during the peak of the 2015 radio flare. From the analysis of the jet component, we derived a Doppler factor of δ_var = 28.5 ± 8.4, a bulk Lorentz factor of <strong>Γ</strong> = 16.8_-3.1^+3.6, and an intrinsic viewing angle of θ_v = 1.42_-0.52^+1.07 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 <em>B</em>_SSA = 15.3_-14.0^+12.6) mG at the peak of the 2015 radio flare, which is comparable to the equipartition magnetic field strength of <em>B</em>_EQ=43.6_-10.4^+10.6 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.<br></p>