time dependent modeling of agn emission from inhomogeneous jets with particle diffusion and...
TRANSCRIPT
Time dependent modeling of AGN emission from inhomogeneous jets with
Particle diffusion and localized acceleration
Extreme-Astrophysics in an Ever-Changing Universe
19.06.2014, Ierapetra
Xuhui Chen
University of Potsdam & DESYCollaborators:
Martin Pohl (University of Potsdam; DESY, Germany);
Markus Boettcher (North-West Uni., South Africa )
Outline
● Introduction and model setup● Closed boundary scenario● Open boundary scenario● Discussion
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Ultra-fast flares in BL Lacs– small emission region (~10 -4 pc)
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(PKS 2155-304, HESS collaboration 2007)
FSRQs detected above 100 GeV– far away emission region (~pc)
(3C279, MAGIC collaboration, 2008)
Blazar Emission Region
4
Sketch of the 2D cylindrical geometry
2nd order Fermi AccelerationThrough Fokker-Planck equation:
Spatial diffusion of particlesThrough Fick's law:
(Chen et al. 2011,2014)
Radiation: Monte Carlo Comptonization
● Synchrotron radiation
● Synchrotron Self-Comptonization (SSC) including inter-zone illumination and light travel time effects (LTTEs)
Homogeneous magnetic fieldused in this study
Observer. Relativistic beaming
5(Chen et al. 2011,2014)
Outline
● Introduction and model setup● Closed boundary scenario● Open boundary scenario● Discussion
6(Solar Prominence,credit to ESA and NASA)
the acceleration region occupies 2x2 zones
Accelerator in the center--Electron energy density map evolution
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Closed boundary
Accelerator in the center--Zone specific electron energy distribution (EED)
Inner zone--accelerated
Outer zone--cooled
Mid zone
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Closed boundary
Comparison with Mrk 421 data (Abdo et al. 2011)
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Accelerator in the center--Total EED and spectral energy distribution (SED)
Closed boundary
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Closed boundary
Consequences:1. Energy dependent AGN emission region2. Weak pair creation compactness constraint3. SSC has harder spectrum than synchrotron
Accelerator in the center--Energy dependent inhomogeneity
Comparison with Mrk 421 data (Abdo et al. 2011)
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Accelerator in the center--Total EED and spectral energy distribution (SED)
Closed boundary
Spectral index: -0.71, -0.59
If the diffusion is slow...
Spectral hardening at high energy
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Closed boundary
Spectral index: -0.6, -0.51
Outline
● Introduction and model setup● Closed boundary scenario● Open boundary scenario● Discussion
13(Figure from Federrath et al. 2011)
Accelerator in the center
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Open boundary
EED develops into a steady broken power-law
Lower energy particles are injected in the acceleration region, to compensate for the particle loss through escape.
Accelerator in the center
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Open boundary
SED also shows broken power-law
Lower energy particles are injected in the acceleration region, to compensate for the particle loss through escape.
Accelerator away from the center
Spectral break smaller compared tothe 'center' case (magenta line)
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Open boundary
Injection not at the Accelerator
EED at high energy identicalto the 'away' case (orange line)
Open boundary
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Particles are injected in the center;but accelerated close to the boundary
Injection not at the Accelerator
Radio excess in the SED
Open boundary
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Particles are injected in the center;but accelerated close to the boundary
Summary● Localized particle acceleration with diffusive particle escape produces electron distribution that can explain AGN emissions
● Energy dependent inhomogeneity causes the SSC spectrum to be harder than the synchrotron spectrum
● Slow diffusion may lead to spectral hardening of the total EED at high energy
● Acceleration away from the emission center leads to atypical broken power-law electron spectrum with break less than 1.
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Future work
● Simulation of flares with similar setup
● Energy dependent diffusion and acceleration
● Anisotropic diffusion
● Use random acceleration to replace continuous acceleration
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