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

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 delta(var) = 28.5 +/- 8.4, a bulk Lorentz factor of Gamma=16.8(-3.1)(+3.6), and an intrinsic viewing angle of theta 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 B-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 B-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.