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High-Energy Gamma-Rays and Physical Implication for GRBs in Fermi Era
Katsuaki Asano (Tokyo Institute of Technology)
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Particle Acceleration
Outline Introduction Limit on LIV Jet Acceleration Particle Acceleration
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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
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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
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Standard Picture ISM External Shock Internal Shock
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Afterglow Racusin et al. 2009 Nardini et al. 2009
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Evidence of Collimated Jet
Sideway Expansion Jet Break Stanek et al. 2000 Apparent Energy >1053erg ->Actual Energy erg?
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The most distant object ever confirmed
GRB z=8.2, t=0.6 billion yrs LyαEmitter z=6.964, t=0.78 bill. yrs
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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
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2008/6/11
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GRB C; Spectra Classical Energy Range
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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
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Constraints on Lorentz Invariant Violation
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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
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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.
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Quantum Gravity Test 高エネルギー光子が遅れてくる? ? (LHC BH??)
Smaller MQG -> large time delay?
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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
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“c” is the same with 18 digits!
?? cm/s depends on E? At least MQG,1>Mpl !
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CTA We can expect 1000 photons @ 10 GeV from a GRB. 10 GeV pulse shape
~keV pulse shape Much stronger constraint
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Ultra-relativistic… Jet Acceleration
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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
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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
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Minimum Lorentz factor
GRB > 1200 GRB C > 900
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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.
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Central Engine How to deposit energy without much baryons?
Neutrino pair annihilation? Collimated energy injection can evacuate baryons and make a fireball. Macfadyen & Woosley
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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
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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
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Ultra High Energy Cosmic Rays
Particle Acceleration
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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)
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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?
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GRB ; Spectra Band+ Extra PL
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Extra Component=Afterglow?
2009 GRB
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GeV-MeV correlate? Abdo et al Supporting material
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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
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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
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Proton Synchrotron R=1014 cm Even in this case,
secondary pairs contribute
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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
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Neutrinos from GRB 090510 “Bright” Neutrino
We may need >10-2 erg/cm2 to detect with IceCube.
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GRB B
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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
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