The Primary Output of GRBs David Eichler

1. The Primary Output of GRBs David Eichler

2. My collaborators: Amir Levinson Jonathan Granot Hadar Manis Don Ellison (if time)

3. Which came first, g-rays or baryonic jet?

4. “Slow” sheath of Baryons Ultrarelativistic fireball e.g. Levinson and Eichler 1993

5. Offset observer sees kinematically dimmed, softened emission Prompt Gamma Rays 1/Γ(t) Afterglow Cone baryons

6. Hypothesis The primary output of GRB is gamma rays and pairs. GRB spectra are intrinsically similar – peaking at about 1 MeV, and the apparent difference is due to viewing angle effects.

7. Eiso- peak correlation (Amati et al 2002, Atteia et al 2003) Eiso proportional to peak2

8. Butler et al 2007 threshold

9. Horizontal purple line is Amati relation

10. X-ray flashes predicted to be as frequent as GRB if beam has a non-trivial morphology e.g. annulus. Observer outside of extended beam – offset angle less than or comparable to opening angle of beam - sees diminished Eiso and npeak as per the Amati et al relation, However, there must be many such viewers. So consider a beam shape that accommodates many such viewers by having lots of perimeter relative to solid angle….e.g. annulus.

11. Off-axis Viewing as Grand Eiso- peak Correlate Viewer outside annulus annulus Pencil beam 

12. Inside annulus

13. Choosing an annulus with outer opening angle about 0.1 radians , thickness about 0.03, and G ~ 102 , and standard cosmology gives a distribution of ( cosmological redshift uncorrected ) Epeak that is flat, as observed (Eichler and Levinson 2004).

15. XRF’s GRB’s 10 KeV 1 MeV

16. Apparent Gamma ray efficiencies (i.e. apparent gamma ray energy E to . apparent blast energy EK)

17. Plotting gamma ray efficiency Eg/EB– gamma ray energy to inferred blast energy - with and without viewing angle correction shows a qualitative difference in the ordering of the data. (Eichler and Jontof-Hutter 2005) With the viewing angle correction the gamma rayefficiencies separate into two classes. The majority (17/22, pre-Swift) has Eg/EB ~ 7, much higher than estimate without a viewing angle correction.

18. The other - 5 outliers of total sample of 22 (pre-Swift) GRB’s with known redshifts - has Eg/EB ~102. (Even higher) Note that all outliers have Eg/EB >> 1. No outliers in the other direction yet. So even though X-ray afterglow is almost always seen, it does not always show a baryonic output that compares in total energy to the prompt gamma ray emission.

19. So viewing angle correction, assuming universality among primary GRB output, • reduces scatter in Eprompt,g/EK • raises its value

20. 20% “expected” from inner shocks

21. Efficiencies with viewing angle correction

22. Without viewing angle correction, the scatter in gamma ray efficiency is much larger

23. Iuside 1/G afterglow cone Outside 1/G afterglow cone Inside 1/G prompt emission cone Head-on Apparent Eg/7.1Ek

24. Ek estimate from X-ray afterglow depends on time of X-ray measurement Apparent

25. Why is the Ghirlanda relation different from the Amati relation? Eisoproportional to E2peak Eg proportional to E1.5peak

26. Inferred opening angle (x-axis) overbiased for soft GRB?

27. If afterglow theory is correct INFERRED opening angle is overestimated for off-beam viewing by npeak1/4 . This explains the npeak1/2 difference between the Amati and Ghirlanda relations (Levinson and Eichler 2005).

28. Eiso- peak2 correlation (Amati et al 2002, Atteia et al 2003) Eigmma - peak1.5 (Ghirlanda et. al 2004)

29. q = K tb3/8EB-1/8, so the “beaming correction” made by Frail, [K tb3/8Eiso-1/8 ]2, should be proportional to (Eiso/EB)1/4 or npeak1/2. which is exactly the difference between the Amati and Ghirlanda relations!. Does this support the physical interpretations of q =K tb3/8EB-1/8 and Eiso/ npeak2 ? What we know is that Eiso [K tb3/8Eiso-1/8 ]2 and Eiso/ npeak2 each have considerably less scatter thanEiso, npeak2 separately. If you believe that each has a physical basis, then you probably have to believe that the Ghirlanda relation differs from the Amati one by npeak1/2

30. What we know is that (Frail) Eiso [K tb3/8Eiso-1/8 ]2, (i.e. tb3/4Eiso3/4) and (Amati et al) Eiso/npeak2 (Eiso3/4/npeak3/2 ) each have considerably less scatter thanEiso, npeak2 separately. If you believe each separately, then you probably have to believe the Ghirlanda relation, tb3/4Eiso3/4 /npeak3/ 2 .

31. Although this is a mathematical tautology, it makes sense that opening angle (function of host star?) and viewing angle should vary from one GRB to the next, even if spectra and primary energy output are universal. Accounting for each reduces the scatter; accounting for both reduces scatter even more. .

32. So, with the viewing angle interpretation, most everybody should be happy. Amati et al and Ghirlanda et al should both be happy because they are both right. Frail et al should be happy that an additional effect, besides opening angle correction, explains residual dispersion in Eiso.

33. Viewing angle proponents should be happy that no ad hoc intrinsic dependence of npeak needs to be invoked to understand Amati et al relations and the like.

34. Why is X-ray afterglow almost always seen within several hours?

35. Because the 1/G spread in the afterglow emission cone is wider, after several hours, than that of the prompt emission, and is wide enough to cover most relevant viewing angles.

36. High E/EK outlier Off set viewer sees slower decline (or possibly rise) in X-ray afterglow during several minutes to hours than on beam viewer. (Eichler 2005)

37. ENTER SWIFT

38. Eichler and Granot, 2006

39. Eichler and Granot, 2006

40. Many authors had predicted delayed afterglow for offset viewers. The surprise from Swift was that is came even when the gamma ray emission was bright and hard (e.g. GRB 050315). One interpretation: Gamma-ray bright, baryon poor line of sight (not expected if baryon KE is primary). Supported by Dec. 27, 2004 giant flare from SGR 1806-20. Prompt gamma rays could not have been seen if they had been mixed in with the baryons.

41. 1 Τ(t1) Fast Rise, Slow Decay Subpulses from scattering off slow, accelerating baryonic clouds. Cloud accelerated by photons pressure of Poynting flux Observer

42. 1 Τ(t2) FRED’s Later, Observer

43. 1 Τ(t3) FRED’s Still later… Observer

46. Optically thin scattering cloud

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

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

49. 1 Τ(t1) FRED’s Optically thick cloud accelerated by photon pressure of Poynting flux Observer shadow Backscattered radiation relativistically beamed in observer frame

50. 1 Τ(t1) FRED’s Optically thick cloud accelerated by photon pressure of Poynting flux Observer shadow Backscattered radiation relativistically beamed in observer frame