The jets emanating from the centers of active galactic nuclei (AGN) are among the most energetic objects in the universe. Investigating how the morphology of the jets synchrotron emission depends on the magnetic nature of the jets relativistic plasma
is fundamental to the comparison between numerical simulations and the observed polarization of relativistic jets. Through the use of 3D relativistic magnetohydrodynamic (RMHD) jet simulations (computed using the PLUTO code) we study how the jets synchrotron emission depends upon the morphology of the jets magnetic field structure. Through the application of polarized radiative transfer and ray-tracing (via the RADMC-3D code) we create synthetic radio maps of the jets total intensity as well as the linearly and circularly polarized intensity for each jet simulation. In particular, we create synthetic ray-traced images of the jets polarized synchrotron emission when the jet carries a predominantly poloidal, helical, and toroidal magnetic field. We also explore several scaling relations in which the underlying electron power-law distribution is set proportional to: (i) the jets thermal plasma density, (ii) the jets internal energy density, and (iii) the jets magnetic energy density. We find that: (i) the jet emission is edge brightened when the magnetic field is toroidal in nature and spine brightened when the magnetic field is poloidal in nature, (ii) the circularly polarized emission exhibits both negative and positive signs for the toroidal magnetic field morphology at an inclination of 45{deg} as well as 5{deg}, and (iii) the relativistic jets emission is largely independent of different emission scaling relations when the ambient medium is excluded.
Low ($lesssim 1%$) levels of circular polarization (CP) detected at radio frequencies in the relativistic jets of some blazars can provide insight into the underlying nature of the jet plasma. CP can be produced through linear birefringence, in which
initially linearly polarized emission produced in one region of the jet is altered by Faraday rotation as it propagates through other regions of the jet with varying magnetic field orientation. Marscher has begun a study of jets with such magnetic geometries using the Turbulent Extreme Multi-Zone (TEMZ) model, in which turbulent plasma crossing a standing shock in the jet is represented by a collection of thousands of individual plasma cells, each with distinct magnetic field orientations. Here we develop a radiative transfer scheme that allows the numerical TEMZ code to produce simulated images of the time-dependent linearly and circularly polarized intensity at different radio frequencies. In this initial study, we produce synthetic polarized emission maps that highlight the linear and circular polarization expected within the model.
Blazars exhibit flares across the entire electromagnetic spectrum. Many $gamma$-ray flares are highly correlated with flares detected at longer wavelengths; however, a small subset appears to occur in isolation, with little or no correlated variabili
ty at longer wavelengths. These orphan $gamma$-ray flares challenge current models of blazar variability, most of which are unable to reproduce this type of behavior. Macdonald et al. have developed the Ring of Fire model to explain the origin of orphan $gamma$-ray flares from within blazar jets. In this model, electrons contained within a blob of plasma moving relativistically along the spine of the jet inverse-Compton scatter synchrotron photons emanating off of a ring of shocked sheath plasma that enshrouds the jet spine. As the blob propagates through the ring, the scattering of the ring photons by the blob electrons creates an orphan $gamma$-ray flare. This model was successfully applied to modeling a prominent orphan $gamma$-ray flare observed in the blazar PKS 1510$-$089. To further support the plausibility of this model, Macdonald et al. presented a stacked radio map of PKS 1510$-$089 containing the polarimetric signature of a sheath of plasma surrounding the spine of the jet. In this paper, we extend our modeling and stacking techniques to a larger sample of blazars: 3C 273, 4C 71$.$01, 3C 279, 1055$+$018, CTA 102, and 3C 345, the majority of which have exhibited orphan $gamma$-ray flares. We find that the model can successfully reproduce these flares, while our stacked maps reveal the existence of jet sheaths within these blazars.
Blazars exhibit flares across the electromagnetic spectrum. Many $gamma$-ray flares are highly correlated with flares detected at optical wavelengths; however, a small subset appears to occur in isolation, with little or no variability detected at lo
nger wavelengths. These orphan $gamma$-ray flares challenge current models of blazar variability, most of which are unable to reproduce this type of behavior. We present numerical calculations of the time-variable emission of a blazar based on a proposal by Marscher et al. (2010) to explain such events. In this model, a plasmoid (blob) propagates relativistically along the spine of a blazar jet and passes through a synchrotron-emitting ring of electrons representing a shocked portion of the jet sheath. This ring supplies a source of seed photons that are inverse-Compton scattered by the electrons in the moving blob. The model includes the effects of radiative cooling, a spatially varying magnetic field, and acceleration of the blobs bulk velocity. Synthetic light curves produced by our model are compared to the observed light curves from an orphan flare that was coincident with the passage of a superluminal knot through the inner jet of the blazar PKS 1510$-$089. In addition, we present Very Long Baseline Array polarimetric observations that point to the existence of a jet sheath in PKS 1510$-$089, thus providing further observational support for the plausibility of our model. An estimate of the bolometric luminosity of the sheath within PKS 1510$-$089 is made, yielding $L_{rm sh} sim 3 times 10^{45} ~ rm erg ~ rm s^{-1}$. This indicates that the sheath within PKS 1510$-$089 is potentially a very important source of seed photons.
