FilamenTATION INSTABILITIES IN RELATIVISTIC PLASMA

1. Almog Yalinewich FilamenTATION INSTABILITIES IN RELATIVISTIC PLASMA

2. Introduction Theoretical background Numerical results Conclusions Table of contents

3. 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 Gamma ray bursts

4. 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 GRB afterglow

5. Progenitor explodes Relativistic jets shoot out Afterglow model

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

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

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

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

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

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

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

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

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

15. Early time behaviour

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

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

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

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

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

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

22. Introduction Theoretical background Numerical results Conclusions Table of contents

23. 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 conclusions

24. Questions