1. High-Energy Gamma-Rays and Physical Implication for GRBs in Fermi Era
Katsuaki Asano
(Tokyo Institute of Technology)

2. Particle Acceleration
Outline
Introduction
Limit on LIV
Jet Acceleration
Particle Acceleration

3. Gamma-Ray Burst The most luminous explosion in the universe
erg/s
Reference:
Sun erg/s
Ｘ-ray star 1038 erg/s
Supernova, Galaxy 1043 erg/s
AGN 1046 erg/s
SGR 1047 erg/s
Light Curve

4. GRB rate Supernova rate ～ 2.4x105 Gpc-3yr-1 (60% II, 30% Ia,
10% type Ib/c)
Hypernova ～500 Gpc-3yr-1
GRB （Jet corrected） ～20 Gpc-3yr-1
～1 detection/day

5. Standard Picture
ISM
External Shock
Internal Shock

6. Afterglow
Racusin et al. 2009
Nardini et al. 2009

7. Evidence of Collimated Jet
Sideway Expansion
Jet Break
Stanek et al. 2000
Apparent Energy >1053erg ->Actual Energy erg?

8. The most distant object ever confirmed
GRB z=8.2, t=0.6 billion yrs
LyαEmitter
z=6.964, t=0.78 bill. yrs

9. Open Problems Emission Mechanism (Synchrotron?)
High Efficiency
Spectrum
Central Engine (Death of Massive Star?)
Progenitor
Energy Release
Jet Acceleration & Collimation
Afterglow (External Shock?)
Spectrum & Time Evolution

10. 2008/6/11

11. GRB C; Spectra
Classical Energy Range

12. Famous Fermi/LAT GRBs GRB 080825C GRB 080916C GRB 081024B GRB 090510
First LAT GRB, delay for>100MeV
GRB C
Eiso=8.8x1054 z=4.35, delay
GRB B
First short LAT GRB, delay
GRB
z=0.903, delay?, extra component
GRB B
Eiso=4x1054 z=1.822 , extra component

13. Constraints on
Lorentz
Invariant
Violation

14. Measuring the Speed of Light
GRBs: Bright Distant Objects
with Emissions of Wide Energy Ranges
-> Ideal to measure the difference of “c”!
Loop quantum gravity?
NYTimes
’09 Oct. 28

15. Motivation How to reconcile gravitation with quantum mechanics?
-> Classical symmetric properties will be sacrificed?
(Spontaneously? Effectively in 4-D?)
Effective Field Theory (Colladay & Kostelecky 1998)
CPT violating
CPT conserving
Photon velocity
CPT symmetry kills the term.

16. Quantum Gravity Test 高エネルギー光子が遅れてくる？ ? (LHC BH??)
Smaller MQG -> large time delay?

17. GRB 090510 Short GRB Precursor Delay z=0.903 (traveling 7.3 Bill. yrs)
8keV-260keV
260keV-5MeV
z=0.903
(traveling 7.3 Bill. yrs)
Eiso=1053erg
>100MeV
>1GeV
31GeV, 3.4GeV

18. “c” is the same with 18 digits!
?? cm/s
depends on E?
At least MQG,1>Mpl !

19. CTA We can expect 1000 photons @ 10 GeV from a GRB. 10 GeV pulse shape
～keV pulse shape
Much stronger constraint

20. Ultra-relativistic…
Jet
Acceleration

21. GRB 080916C Long GRB Delay z=4.35 Eiso=8.8x1054erg ～5xMsunc2 13GeV
8keV-260keV
GRB C
260keV-5MeV
Long GRB
Delay
z=4.35
Eiso=8.8x1054erg
>100MeV
～5xMsunc2
>1GeV
13GeV
3GeV

22. Compactness Problem
If gamma-rays are emitted isotropically, GeV photons cannot escape because electron-positron pairs should be created via photon-photon collision.
→Inconsistent with obs.
In the comoving frame…
If the sources are
ultra-relativistic…
(We have observed
blue-shifted photons)
X-ray
No high energy photons

23. Minimum Lorentz factor
GRB > 1200
GRB C > 900

24. Fireball Acceleration
Radiation dominated plasma; huge amount of electron-positron pairs and photons, and small amount of protons.
Adiabatic Expansion; Thermal Energy -> Bulk Kinetic Energy
Ｆｉｒｅｂａｌｌ Evolution:
is required.

25. Central Engine How to deposit energy without much baryons?
Neutrino pair annihilation?
Collimated energy injection can evacuate baryons and make a fireball.
Macfadyen & Woosley

26. Lack of Thermal Emission
The fireball becomes optically thin as it expands.
-> Thermal Photons
GRB C
GRB090102
Optical polarization is reported.
-> Strongly Magnetized Plasma?
Zhang & Pe’er 2009

27. Poynting Flux Dominated Jet?
Magnetic Energy dominates the bulk kinetic energy
-> can be relativistic.
MHD turbulences (MRI) enhance the magnetic field.
Weak points:
Hard to produce shocks
Hard to induce magnetic reconnection
How to convert kinetic energy into photons??
McKinney & Blandford 2009

28. Ultra High Energy Cosmic Rays
Particle
Acceleration

29. Ultra High Energy Cosmic Ray (UHECR)
Where is the accelerator??
(Strong magnetic field or large size to confine particles)
n(E)∝E-3
Energy
distribution
>1020eV
Ref:
7 TeV by LHC
AGN? (low number density)

30. Highest Accelerator=GRB?
We need ergs/Mpc3/yr to explain UHECRs
See e.g. Murase et al. 2008
We may need Up/Ue>20.
If GRB rate is 0.05 Gpc-3/yr, Up/Ue>100
Hidden Energy?

31. GRB ; Spectra
Band+ Extra PL

32. Extra Component=Afterglow?
2009
GRB

33. GeV-MeV correlate?
Abdo et al Supporting material

34. Signature of Proton Acceleration?
Hadronic Cascade
p＋γ→p(n)＋π0(π+)
p＋γ→p+ e＋ + e-
π0→γ＋γ, π＋→μ＋ +νμ
μ＋ →e＋ + νμ + νe
Synchrotron from π＋ ,μ＋, e±
Inverse Compton from π＋ ,μ＋, e±
γ＋γ→ e＋ + e-
Synchrotron Self Absorption

35. Cascade due to photopion production
Asano, Guiriec & Meszaros 2009
Cascade due to photopion production
gg-absorption
R=1014 cm
G=1500
Band component
3.4GeV
Synchrotron and Inverse Compton due to secondary electron-positron pairs

36. Proton Synchrotron R=1014 cm Even in this case,
secondary pairs contribute

37. Proton Dominated GRBs
Favorable for ultra high-energy cosmic ray production
Asano, Inoue & Meszaros 2009
GRB
10keV
1MeV
1GeV
The extra component: Hard spectrum: Index -1.6
Comparable flux to the Band flux
10 keV

38. Neutrinos from GRB 090510 “Bright” Neutrino
We may need >10-2 erg/cm2 to detect with IceCube.

39. GRB B

40. Conclusion LIV with n=1 may be excluded.
Lorentz factor of GRB Jets > 1000.
Possible signature of UHECR production.
New Theoretical Challenge:
Delayed onset of GeV Emission
GRB C
GRB