A Near Magnetic-to-kinetic Energy Equipartition Flare from the Relativistic Jet in AO 0235+164 during 2013-2019

Abstract

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 (DCF) analysis, we find a significant (>95%) correlation between radio and ${\hat{I}}^3$-ray light curves with flares at longer wavelengths following flares at shorter wavelengths. We identify a new jet component in 43 GHz VLBA 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 $\hat{I}{´}_{\mathrm{var}}=28.5\pm 8.4$, a bulk Lorentz factor of $\hat{I}“=16.8_{-3.1}^{+3.6}$, and an intrinsic viewing angle of $\hat{I}{¸}_{\mathrm{v}}=1.42_{-0.52}^{+1.07}\text{ degrees}$. 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 $B_{\mathrm{SSA}}=15.3_{-14.0}^{+12.6}$ mG at the peak of the 2015 radio flare, which is comparable to the equipartition magnetic field strength of $B_{\mathrm{EQ}}=43.6_{-10.4}^{+10.6}$ 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.

13 pages, 11 figures, 4 tables; Accepted for publication in MNRAS