Numerical Modeling of Electromagnetic Radiation from AGN Jets

Based on

-ray emission and spectral evolution of pair plasmas in AGN jets

Bottcher et al. Astronomy and Astrophysics Vol. 324 1997

Giridhar Nandikotkur

Numerical Modeling of Electromagnetic Radiation from AGN Jets

• What are Active Galactic Nuclei (AGN)? Structure Historical Existence

• Physical Processes Experiment leading to theory

a chronological journey Current Status of theoretical methods

• First step- a small one

What are Active Galactic Nuclei (AGNs)?

• Historical Existence Extra-galactic

measured redshifts Extremely bright and violent

presence of jets at all wavelengths

Estimated energy more than of order of 10^60 ergs!

Something gravitational in nature Sharp rise in Luminosity towards the center

Massive object at the center-black hole?

What are Active Galactic Nuclei (AGNs)?

• Structure Black hole at the center Accretion disc Jet Clouds at some distance Ordered magnetic filed lines emanating from BH

Physical Processes• Synchrotron Radiation

suggested by polarization measurements

Experimentally observation: Power law energy spectrum

can be produced by power law distribution of electrons

Physical Processes Photon Scattering by Inverse Comton

emission

Thompson scattering - non-relativistic

Compton Scattering - relativistic: Klein-Nishina

Physical Processes• Broadband Spectrum

Synchrotron radiation has a peak and (dF/dlog) = F vs. will show a peak. Peak around optical-UVfalls towards UV, Xrays

• Compton Gamma Ray Observatory Launch 1991 Detection of sources with high energy gamma ray emission Bulk of their luminosity in Gamma rays A second peak in the broad band spectrum

Explanation by Inverse Compton emission

Torus

BLR

Ac. Disk B. Hole

Electrons

Photons

SED for FSRQ

Peak 1: Synchrotron Radiation

Peak 2. Accretion Disk Black Body

Peak 3. Self Synchrotron Emission (SSC)

Peak 4. External Comption Disk (ECD)

Peak 5. External Compton clouds (ECC)

Theoretical ApproachesNumerical Model.

Assume an injected leptonic (e+ e-)

plasma blob with power law distribution.

Evolution of photon and electron distributions using emission and absorption processes.

Power Law: N()d = C -s dC: Normalization constant N()d = No

Energy Losses

(d /dt)synchrotron ; (d /dt)SSC ; Numerical Integration

(d /dt)ECD ; (d /dt)ECC ;

Change in particle distribution

t = 0 + t * (d /dt)ECD Forward Euler

Photon Spectrum at each time step

Power Law distribution. Log-Log Plot

-1.50

-1.00

-0.50

0.00

0.50

0.0 2.0 4.0 6.0 8.0

Log(Gamma)

Lo

g(N

)

Power Law Distribution

0.0

2.0

4.0

6.0

0 5000 10000 15000 20000 25000

Gamma: Lorentz factor

N(G

am

ma

)

Simulation of ECD process

Scattering of accretion disk photons of electrons

mathematica postscript

Convergence of Trapezoidal Rule

-20

-15

-10

-5

0

5

10

0 2000 4000 6000 8000 10000 12000

Number of steps

Lo

g (

Dif

fere

nce

)

Cos(x) (0-Pi/2)

Cos(x) (0,Pi)

2x + 3x^2 +5x^4

Power Law

Energy Loss Rate from Compton Scattering of Disk Radiation

-1

0

1

2

3

4

5

6

3 3.5 4 4.5 5 5.5 6 6.5

Lorentz factor of electrons

En

erg

y L

oss

Ra

te

ELR

Has to match exactly with the paper.If not, find the parameter that is differentin the initialization

Future Work

• Include other processes.

• Generate Photon Spectrum

• Explore Gaussian Quadrature to Numerically integrate.

• Ambitious Target: 3 months!