So you Think you can Explain GRB? David Eichler

1. So you Think you can Explain GRB? David Eichler

2. My collaborators: Amir Levinson Jonathan Granot Dafne Guetta Hadar Manis Samir Mandal

3. Outstanding Questions about GRB

4. Outstanding Questions about GRB (to be shot out rapid fire, and punctuated with “Huh?..Huh?...)

5. Why are GRB not squelched by baryon contamination? • Strange matter sources (Paczynski and coworkers, Usov) • 2) Axion decay (Kluzniak) • 3) Event horizons, GR needed (Levinson and Eichler) • 4) Centrifugal barrier, GR unnecessary, (several authors) • 5) Patience, wait ~100 s for baryons to settle down, (as for magnetars) then use magnetocentrifugal ejection (Thompson….?)

6. Why does spectrum typically peak at several hundred KeV? Selection effects? Coincidence? Photospheric emission? pair controlled? * (DE 1994, Thompson 1995, Levinson and Eichler 2000, Ryde,2004, Meszaros and Rees 2000, 2005, Pe’er, Meszaros and Rees 2008) *e.g.Cavalo and Rees 1978

7. What carries the energy from the collapsed object to the emitting radius – EM flux or baryonic material? Does the photon pair fireball derive from or provide the kinetic energy of the baryons? Do the photons and baryons in GRB always coincide in direction?If not, then photons with hardly any baryons is possible. ?

8. Did the matter that the gamma ray photons last interact with come from the collapsed object or from the host environment? If from host environment, what is the nature of the interaction? How do the baryons acquire energy from the fireball

9. Does Lorentz factor saturate before or after photosphere? Rsat >, < Rph? If prompt gamma ray energy comes from kinetic energy in matter, then probably Rsat < Rph If Rsat > Rph, it means that the matter is still accelerating at the photosphere, hence kinetic energy of baryonic matter probably comes from EM /pair pressure. Are there any observational clues?

10. Why do Fermi LAT /EGRET detections show soft to hard evolution?Harder emission made further downstream?

11. Why do subpulses show hard to soft evolution? Why are spectral lagsinversely correlated with luminosity L for long bursts? Why the spectral lag -L correlation for long bursts, not short ones? Why is the Amati “relation” one sided? Why does it not apply to afterglow fluences, i.e. why does it apply to photon flux but not baryonic kinetic energy? Why does duration of flat phase of afterglow correlate with spectrum?

12. Why are short GRB so far off the Amati relation? If short GRB are due to short central engine activity, why do many of them have long X-ray tails? Why not all of them?

13. Why is GRB 060218 both the longest duration burst (longer than this talk) and one of the closest? What are the odds it is just a coincidence?

14. Basic picture of central engine “Slow” sheath of Baryons Ultrarelativistic fireball, nearly baryon free, except for neutron leakage e.g. Levinson and Eichler 1993

15. Rossweg and Ramirez-Ruiz

16. How sharp is the distinction between the baryon poor and baryon rich parts of a GRB event? Event horizon is either/or, and might provide sharper transverse gradients than a Newtonian centrifugal barrier in the presence of strong viscosity. Needs careful theoretical study. Could there be opportunity for observational investigation? Can we probe the transition from baryon rich to baryon poor? Can we probe the transition from GRB to NQGRB depending on viewing angle?

17. One possible observational consequence: Neutrons can decouple from protons at some radius (Derishev 1999). If parameters vary sharply at some magnetic surface, then pickup ex- neutrons receive enormous energies in lab frame (Eichler and Levinson 1999)– get harder neutrino spectrum than from shock acceleration. Most of the GRB energy could come out as UHE neutrinos.

18. Collisional Avalanche Neutron mist n n n n Neutron free streaming boundary Nn about A/ =1049A12

19. Collisional Avalanche n n n n

20. Collisional Avalanche n 1015 eV neutrinos n n n

21. Collisional Avalanche- solves s problem conversion efficiency problem, gives very hard spectra n 1015 eV neutrinos Could be the main output. Spectrum much harder than for shock acceleration n n n

22. What do NQGRBs look like? Dirty fireballs? Kinematically softened gamma rays ? Was the dominant emitting matter beamed directly at the observer?

23. Rossweg and Ramirez-Ruiz

24. What do NQGRBs look like? Dirty fireballs? Kinematically softened gamma rays ? Was the dominant emitting matter beamed directly at the observer? The Amati relation may provide clues.

26. The Amati relation interpreted as a viewing angle effect. Soft photons always spray out beyond 1/G cone. Near perimeter observers see Amati relation 1/G cone

27. Patchy jet also works if patches have sharp edges

28. Amati relation according to Butler et al 2007 Head on Pencil beam Detection threshold Harder Extended source, near perimeter viewing brighter

29. Amati relation according to Butler et al 2007

30. Amati relation according to Butler et al 2007 Detection threshold Scattering of slow material Extended source, near perimeter viewing

31. Amati relation according to Butler et al 2007 Pencil beam Detection threshold Constant photon number. e..g. dirty fireballs

32. WHERE ARE THE NQGRBs?? ??? g-ray X-ray

33. Observer Jet So if you believe the viewing angle interpretation of the Amati relation, then you have to believe that the directly oriented emission is subdominant, i.e. sharp edge

34. Amati relation according to Butler et al 2007 Pencil beam Detection threshold Constant photon number

35. Photospheric emission does not deny internal shocks Non-thermal emission in GRB beyond disputesince SMM.

36. Is the emission at 300 KeV from a pair- controlled photosphere?The baryons could come from the host environment after the fireball is going strong.

37. But wait: If there are enough baryons to account for non-thermal gamma rays via shock acceleration beyond the photosphere, (even if injected beyond photosphere), why do they not obscure the photospheric emission?

38. But wait: If there are enough baryons to account for non-thermal gamma rays via shock acceleration beyond the photosphere, (even if injected beyond photosphere), why do they not obscure the photospheric emission? I’m glad you asked.

39. But wait: If there are enough baryons to account for non-thermal gamma rays via shock acceleration beyond the photosphere, (even if injected beyond photosphere), why do they not obscure the photospheric emission? Partial coverage? (if all else fails).

40. But wait: If there are enough baryons to account for non-thermal gamma rays via shock acceleration beyond the photosphere, (even if injected beyond photosphere), why do they not obscure the photospheric emission? Maybe they do sometimes, so what?

41. But wait: If there are enough baryons to account for non-thermal gamma rays via shock acceleration beyond the photosphere, (even if injected beyond photosphere), why do they not obscure the photospheric emission? Back-end photospheres: slow baryon acceleration,hard to soft evolution, spectral lags, outliers to the Amati relation, subluminous events, short hard bursts with long X-ray tails, may all fit into a single picture that addresses this question

42. Back-facing photosphere Lorentz transformation

43. Sharply rising FRED’s Optically thick cloud? Observer Backscattered radiation in frame of cloud. Shadow in frame of cloud

44. shadow 1 Τ(t1) FRED’s Optically thick cloud accelerated by photon pressure of Poynting flux Observer Backscattered radiation relativistically beamed in observer frame

45. 1 Τ(t1) FRED’s Optically thick cloud accelerated by photon pressure of Poynting flux Observer shadow Backscattered radiation relativistically beamed in observer frame

46. 1 Τ(t1) FRED’s Optically thick cloud accelerated by photon pressure of Poynting flux Observer shadow Backscattered radiation relativistically beamed in observer frame

47. Optically thin scattering cloud

48. Optically thin scattering cloud

49. theory

50. Optically thick cloud Blocked by high optical depth Switches on just when q= 1/G.