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High-Energy Gamma-Rays and Physical Implication for GRBs in Fermi Era

High-Energy Gamma-Rays and Physical Implication for GRBs in Fermi Era. Katsuaki Asano (Tokyo Institute of Technology). Outline. Introduction Limit on LIV Jet Acceleration Particle Acceleration. Gamma-Ray Burst. The most luminous explosion in the universe. 10 52 -10 54 erg/s. Reference:

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High-Energy Gamma-Rays and Physical Implication for GRBs in Fermi Era

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

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

  3. Gamma-Ray Burst The most luminous explosion in the universe 1052-1054 erg/s • Reference: • Sun 3.9 1033 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 1051 erg?

  8. The most distant object ever confirmed GRB 090423 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 080916C; Spectra Classical Energy Range

  12. Famous Fermi/LAT GRBs • GRB 080825C • First LAT GRB, delay for>100MeV • GRB 080916C • Eiso=8.8x1054 erg @ z=4.35, delay • GRB 081024B • First short LAT GRB, delay • GRB 090510 • Short @ z=0.903, delay?, extra component • GRB 090902B • Eiso=4x1054 erg @ 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 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! 29979245800.0000000?? 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 8keV-260keV 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 090510 > 1200 GRB 080916C > 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 080916C 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 6-8 1043 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 090510; Spectra Band+ Extra PL

  32. Extra Component=Afterglow? 2009 GRB 090510

  33. GeV-MeV correlate? Abdo et al. 2009 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. 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 090510 10keV 1MeV 1GeV The extra component: Hard spectrum: Index -1.6 Comparable flux to the Band flux Excess @ 10 keV

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

  39. GRB 090902B

  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 080916C GRB 090510

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