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

Light Curve

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

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

Standard Picture

1000100 Internal Shock External Shock

ISM

Afterglow

Nardini et al. 2009Racusin et al. 2009

tf X

Evidence of Collimated Jet

Stanek et al. 2000

Sideway Expansion

/1

//3/

0

com0 RtcctR

Jet Break

Apparent Energy >1053erg ->Actual Energy 1051 erg?

The most distant object ever confirmed

GRB 090423 z=8.2, t=0.6 billion yrsLyαEmitter z=6.964, t=0.78 bill. yrs

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

2008/6/11

GRB 080916C; Spectra

Classical Energy Range

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

Lorentz Invariant Violation

Constraints on

Measuring the Speed of Light

GRBs: Bright Distant Objectswith Emissions of Wide Energy Ranges -> Ideal to measure the difference of “c”!

NYTimes ’09 Oct. 28

Loop quantum gravity?

MotivationHow 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

2

2QG,2

ph

2QG,1

phph 2

31

cM

E

cM

Ecv

Photon velocity

CPT symmetry kills the term.

Quantum Gravity Test

nQGcMEEf )/()( 2

高エネルギー光子が遅れてくる？

PlQG MM ?

2& mm10for TeV d.RM

Smaller MQG -> large time delay?

(LHC BH??)

GRB 090510

Short GRB Precursor Delay

z=0.903 (traveling 7.3 Bill. yrs)Eiso=1053erg

8keV-260keV

260keV-5MeV

>100MeV

>1GeV31GeV, 3.4GeV

At least MQG,1>Mpl !

“c” is the same with 18 digits!

29979245800.0000000?? cm/s depends on E?

CTA

We can expect 1000 photons @ 10 GeV from a GRB.

10 GeV pulse shape～ keV pulse shape

Much stronger constraint

Jet Acceleration

Ultra-relativistic…

GRB 080916C

>100MeV

>1GeV

260keV-5MeV

8keV-260keV

z=4.35Eiso=8.8x1054erg

Long GRB Delay

3GeV

13GeV

～ 5xMsunc2

Compactness Problem

X-ray

No high energy photons

In the comoving frame…If the sources are ultra-relativistic…(We have observed blue-shifted photons)

If gamma-rays are emitted isotropically, GeV photons cannot escape because electron-positron pairs should be created via photon-photon collision.

→Inconsistent with obs.

Minimum Lorentz factor

1000 GRB 090510 > 1200GRB 080916C > 900

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:

rTr /1 , 1000/ 2 McE is required.

Central Engine

Macfadyen & Woosley

How to deposit energy without much baryons?

Neutrino pair annihilation?

Collimated energy injection can evacuate baryons and make a fireball.

Lack of Thermal Emission

Zhang & Pe’er 2009

GRB090102 Optical polarization is reported. -> Strongly Magnetized Plasma?

GRB 080916C The fireball becomes optically thin as it expands. -> Thermal Photons

Poynting Flux Dominated Jet?

McKinney & Blandford 2009

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??

Particle Acceleration

Ultra High Energy Cosmic Rays

Ultra High Energy Cosmic Ray (UHECR)

Energy distribution

>1020eV

n(E)∝E-3

Where is the accelerator?? (Strong magnetic field or large size to confine particles)

Ref: 7 TeV by LHC

AGN? (low number density)

Highest Accelerator=GRB?

eV10@ 19

We need 6-8 1043 ergs/Mpc3/yr to explain UHECRs

epacc UU /ξ

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?

GRB 090510; Spectra

Band+ Extra PL

Extra Component=Afterglow?

GRB 090510

2009

GeV-MeV correlate?

Abdo et al. 2009 Supporting material

Signature of Proton Acceleration?

• 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

Hadronic Cascade

Cascade due to photopion production

3.4GeV

R=1014 cm=1500

200/

10/ 3

LL

UU

p

B

Synchrotron and Inverse Compton due to secondary electron-positron pairs

Band component

-absorption

Asano, Guiriec & Meszaros 2009

Proton Synchrotron

R=1014 cm

300// LLLL Bp 310

Even in this case, secondary pairs contribute

Proton Dominated GRBsFavorable for ultra high-energy cosmic ray production

10keV 1MeV 1GeV

GRB 090510

Asano, Inoue & Meszaros 2009 UU p

The extra component: Hard spectrum: Index -1.6 Comparable flux to the Band flux Excess @ 10 keV

Neutrinos from GRB 090510

[eV]

f() [erg/cm2/s]

Muon-decay

Pion-decay

Pair Cascade

Proton Synchrotron

1014 1015 1016 1017 101810-7

10-6

10-5

We may need >10-2 erg/cm2 to detect with IceCube.

“Bright” Neutrino

GRB 090902B

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