We present observations of the blazar 3C 279 at 22 GHz by the space-based very long baseline interferometry mission RadioAstron from January 15, 2018. We reconstructed images in both total intensity and fractional polarization using the regularized maximum likelihood method implemented in the eht-imaging library. The electric vector position angles are found to be mostly aligned with the general jet direction, suggesting a predominantly toroidal magnetic field and in agreement with the presence of a helical magnetic field. Ground-space fringes were detected up to a projected baseline length of ∼8 Gλ, achieving an angular resolution of around 26 μas. The fine-scale structure of the relativistic jet is found in our study to extend to a projected distance of ∼180 parsec from the radio core. However, the filamentary structure reported by previous RadioAstron observations from 2014 is not detected in our current study. We discuss potential causes for this phenomenon and present a comparison using public 43 GHz data from the BEAM-ME program showing a significant drop in the jet’s total intensity. We observe that the optically thick core has a brightness temperature of 1.6 × 10¹² K, consistent with equipartition between the energy densities of the relativistic particles and the magnetic field. This yields an estimated magnetic field strength of 0.2 G.

We present total intensity and linear polarization images of OJ 287 at 1.68 GHz, obtained through space-based very long baseline interferometry (VLBI) observations with RadioAstron on April 16, 2016. The observations were conducted using a ground array consisting of the Very Long Baseline Array (VLBA) and the European VLBI Network (EVN). Ground-space fringes were detected with a maximum projected baseline length of ∼5.6 Earth's diameter, resulting in an angular resolution of ∼530 μas. With this unprecedented resolution at such a low frequency, the progressively bending jet structure of OJ 287 has been resolved up to ∼10 parsec of the projected distance from the radio core. In comparison with close-in-time VLBI observations at 15, 43, 86 GHz from MOJAVE and VLBA-BU-BLAZAR monitoring projects, we obtain the spectral index map showing the opaque core and optically thin jet components. The optically thick core has a brightness temperature of ∼1013 K, and is further resolved into two sub-components at higher frequencies labeled C1 and C2. These sub-components exhibit a transition from optically thick to thin, with a synchrotron self-absorption (SSA) turnover frequency estimated to be ∼33 and ∼11.5 GHz, and a turnover flux density ∼4 and ∼0.7 Jy, respectively. Assuming a Doppler boosting factor of 10, the SSA values provide the estimate of the magnetic field strengths from SSA of ∼3.4 G for C1 and ∼1.0 G for C2. The magnetic field strengths assuming equipartition arguments are also estimated as ∼2.6 G and ∼1.6 G, respectively. The integrated degree of linear polarization is found to be approximately ∼2.5%, with the electric vector position angle being well aligned with the local jet direction at the core region. This alignment suggests a predominant toroidal magnetic field, which is in agreement with the jet formation model that requires a helical magnetic field anchored to either the black hole ergosphere or the accretion disk. Further downstream, the jet seems to be predominantly threaded by a poloidal magnetic field.