Center for Astrophysics Research and Technologies Seminar Series
Kinetic- vs Magnetic-driven Blazar Jet Models
Presented by Haocheng Zhang, UNM
Blazars are a type of active galaxy whose jets are directed close to our line of sight. They exhibit strong variability across the entire electromagnetic spectrum, from radio up to TeV gamma-rays. Their radio to optical polarization signatures, which originate from synchrotron emission in a partially ordered magnetic field, show strong variability as well. Two scenarios have been advanced to explain blazar variability: (1) the kinetic-driven model argues that the emission region can drain kinetic energy through shocks that accelerate non-thermal particles and generate flares; and (2) the magnetic-driven model suggests that the magnetic energy can dissipate through current-driven instabilities to fuel the variability. Both models have their merits in understanding blazar spectra and light curves during flares, thus they cannot readily be distinguished. We perform comprehensive polarization-dependent radiation modeling of shocks and kink instabilities in the blazar emission region, based on detailed relativistic magnetohydrodynamic (RMHD) simulations. Our approach involves self-consistent magnetic field evolution, non-thermal particle injection based on the energy release from the RMHD simulation, and detailed radiation transfer including all light travel time effects. Hence our method offers self-consistent time-dependent radiation and polarization signatures from first principles. By comparing the shock and the kink models, we find that while both can interpret the light curves well, the shock model generally creates polarization variations that are too strong compared to the observations. On the other hand, the kink model fits the general polarization fluctuations and polarization angle swings better. We conclude that by coupling first-principle simulations and detailed polarization-dependent radiation modeling, polarization signatures can probe the origin of the blazar jet variability, and offer a general diagnostic of the jet physics, including the energy composition, the particle acceleration, and the magnetic field evolution in the emission region.
2:00 pm, Thursday, October 27, 2016
PAIS-2540, PAIS
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