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

2

Ultra-fast flares in BL Lacs– small emission region (~10 -4 pc)

3

(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

7

Closed boundary

Accelerator in the center--Zone specific electron energy distribution (EED)

Inner zone--accelerated

Outer zone--cooled

Mid zone

8

Closed boundary

Comparison with Mrk 421 data (Abdo et al. 2011)

9

Accelerator in the center--Total EED and spectral energy distribution (SED)

Closed boundary

10

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)

11

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

12

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

14

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

15

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)

16

Open boundary

Injection not at the Accelerator

EED at high energy identicalto the 'away' case (orange line)

Open boundary

17

Particles are injected in the center;but accelerated close to the boundary

Injection not at the Accelerator

Radio excess in the SED

Open boundary

18

Particles are injected in the center;but accelerated close to the boundary

Outline

● Introduction● Closed boundary scenario● Open boundary scenario● Discussion

19

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.

20

Future work

● Simulation of flares with similar setup

● Energy dependent diffusion and acceleration

● Anisotropic diffusion

● Use random acceleration to replace continuous acceleration

21

Reference

Abdo et al. 2011, ApJ, 736,131Chen et al. 2011, MNRAS, 416, 2368Chen et al. 2014, MNRAS, in pressFederrath et al. 2011, ApJ, 731, 62HESS collaboration, ApJ, 664, 71MAGIC collaboration, science, 2008, 320, 1752