2022ApJ...925..139S

The optical radiation emitted by blazars contains contributions from synchrotron radiation by relativistic electrons in the jets, as well as thermal radiation emitted mainly by the accretion disk (AD), the broad-line region (BLR), and the host galaxy. The unpolarized radiation components from the AD, BLR, and host galaxy present themselves by decreasing the total polarization in the optical/ultraviolet (UV) spectrum. A combined model for the spectral energy distribution (SED) and degree of optical/UV polarization is constructed, enabling the disentanglement of the synchrotron and AD components. Our model is applied to the multiwavelength SED and spectropolarimetry observations of the flat-spectrum radio quasar 4C+01.02 (z = 2.1) in its 2016 July-August flaring state and 2017 July-August quiescent state, using data from the Fermi Large Area Telescope, the Southern African Large Telescope, and the Las Cumbres Observatory network of telescopes. By constraining the AD component, the mass of the supermassive black hole is obtained as ∼3 x 10⁹M_☉. Furthermore, the model retrieves the characteristics of the relativistic electron distribution in the jet and the degree of ordering of the magnetic field. Our results highlight the potential of spectropolarimetry observations for disentangling thermal from nonthermal (jet) emission components, thus revealing the physics of particle acceleration and high-energy emission in active galactic nucleus jets.