1. FilamenTATION INSTABILITIES IN RELATIVISTIC PLASMA
Almog Yalinewich
FilamenTATION INSTABILITIES IN RELATIVISTIC PLASMA

2. Table of contents Introduction Theoretical background
Numerical results
Conclusions

3. Gamma ray bursts GRBs are the most luminous flashes since the Big Bang
They last between ~0.01 and ~100 seconds
The nature of their progenitor (engine) is unknown

4. GRB afterglow
The prompt flash is usually followed by a longer wavelength, longer lived afterglow
Can last for months
Though not always detected, it has been proposed that all GRBs are followed by an afterglow

5. Afterglow model
Progenitor explodes
Relativistic jets shoot out

6. Afterglow model – cont’d
Jet collides with ISM/Progenitor wind
Particles reflect from jet front
Jet

7. Afterglow model – cont’d
Electrons thermalise by the plasma instabilities
Plasma instabilities generate magnetic fields
Jet

8. Afterglow model – cont’d
Protons thermalise by the plasma instabilities
Jet

9. Synchrotron radiation
In a constant magnetic field, the trajectory of a charged particle is a helix
The particle radiates perpendicular to the magnetic field

10. Jitter radiation
If the field changes on a length scale smaller than the Larmor radius, the particle moves in a meandering trajectory

11. Afterglow emission
The afterglow emission is predicted quite well by a combination of synchrotron and jitter radiation

12. Weibel instability
Occurs in plasma with anisotropic momentum distribution
Amplifies certain disturbances in the electromagnetic field
Causes current filamentation

13. Table of contents Introduction Theoretical background
Qualitative description
Quantitative description
Numerical results
Conclusions

14. Late time behaviour
Isotropic momentum distribution is the preferred state (equipartition)
In “normal” matter, relaxation occurs via collisions
In collisionless plasma, relaxation occurs via the plasma instabilties

15. Early time behaviour

16. Other instabilities
Besides Weibel, other instabilities can develop in plasmas, e.g. two stream, Buneman, Oblique
They do not amplify magnetic fields

17. Table of contents Introduction Theoretical background
Numerical results
First stage (electron beams)
Secon stage (proton beams & electron bg)
Conclusions

18. Cold beam of equal densities
In the ultra – relativistic regime, the dominant mode is the Weibel mode

19. Cold beams of different densities
When the density ratio drops below ~ 0.6, the dominating instability becomes oblique and electrostatic

20. Cold beam, equal densities, hot bg
An electrostatic instability appears (Buneman)

21. Cold beam, different densities, hot bg
The previous profile is hardly effected by the density ratio

22. Table of contents Introduction Theoretical background
Numerical results
Conclusions

23. conclusions
Type of instability in counter streaming plasmas determined mainly by beam density ratio
Second stage involves simultaneous growth of two modes of instabilities
Magnetic field generation in GRB afterglows is more robust than previously thought

24. Questions