Inverse Compton (IC)

Question 1

Core idea of IC?

Answer 1

Relativistic electron scatters low-energy photon and boosts its energy.

Question 2

Energy Boost

Answer 2

E final ~ gamma^2 E initial

Photon gains roughly gamma^2 energy (electron Lorentz factor)

Question 3

Power Scaling

Answer 3

P ic ~ gamma^2 Urad

where Urad is radiation energy density.

Question 4

Spectrum Shape in relation to Synchrotron?

Answer 4

If electron distribution is:
N(E) ~ E^-p, then Fv ~ v^-(p-1).2 same slope as synchrotron if same electrons.

If two power law bumps with same slope —> IC + Synchrotron from same population.

Question 5

What determines whether synchrotron or inverse Compton dominates?

Answer 5

Compare energy densities!

P ic/ P sync = Urad/ UB

So if U rad > UB —> IC dominates
If UB > Urad —> synchrotron dominates

Question 6

What is cooling time for IC?

Answer 6

t ~ 1/ gamma Urad

Question 7

Klein-Nishina Regime

Answer 7

When gamma E seed > me c^2

Cross section drops. Spectrum becomes softer, IC less efficient. Slope streams beyond (p-1)/2.