Abstract
Abstract 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 × 109 M ⊙. 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.
Highlights
Blazars are a class of jet-dominated Active Galactic Nuclei (AGN) in which one of the jets is closely aligned to our line of sight, leading to strongly Doppler boosted emission received by the observer
The model was fitted to contemporaneous Las Cumbres Observatory (LCO) optical photometry and Southern African Large Telescope (SALT) spectropolarimetry data, complemented by archival radio through UV data of 4C+01.02 in its flaring state from 2016 and quiescent state from 2017
In this paper we describe the development of a code to simultaneously fit the low-frequency Spectral Energy Distribution (SED) and spectropolarimetry data of blazars
Summary
Blazars are a class of jet-dominated (radio-loud) Active Galactic Nuclei (AGN) in which one of the jets is closely aligned to our line of sight, leading to strongly Doppler boosted emission received by the observer. Electron synchrotron emission dominates at low-frequencies and protons are assumed to be accelerated to sufficiently high energies to radiate appreciably. The BH mass estimate by Ghisellini et al (2011), stemmed from a fit to the optical regime in the SED that was strongly dominated by direct AD emission, and expected to yield low degrees of polarization. The transition from low-polarization AD-dominated emission to synchrotron-dominated high-polarization emission is accessible to spectropolarimetry and provides an important constraint unavailable with the SED alone We have detected such a transition in spectropolarimetric observations with SALT, motivating a joint fit to the SED and the spectropolarimetry. The spectropolarimetry observations are fitted simultaneously with the SED to disentangle the spectrum of the synchrotron and AD components and thereby, indirectly, constraining the mass of the BH.
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