Photons and Neutrinos Originating from Accelerated Protons in GRBs

1
Photons and Neutrinos Originating from
Accelerated Protons in GRBs

• Katsuaki ASANO
• (National Astronomical Observatory of Japan)

Collaborators S.Inoue, S.Nagataki, F.Takahara
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Abstract
We show results of our Monte Carlo Simulation.

• There are many ambiguous points in the standard
  GRB model Emission mechanisms, proton
  acceleration efficiency etc.
• Future observations of gamma-rays and neutrinos
  from mesons will justify the standard model, and
  determine the proton acceleration efficiency.

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Gamma-Ray Burst
4
Time Profile
?T
dT
5
Energy Budget
Shock Dissipated Energy
?
Magnetic Field
Acc. Electrons
Acc. Protons
Synchrotron
Gamma-Rays
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Standard Picture of Electron Acceleration
Thermal Electrons
Electron number
Non-thermal
Energy
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Electron-acceleration in the GRB Standard Model
Protons possess most of internal energy
Energy transport and electron-acceleration

• The energy transport process is unknown.
• No thermal electrons!!

Thermal
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Break Energy
Break
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Observed Break Energy
BATSE Data
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Problems in the Theory

• Compactness problemTime Profile
• Internal Shock Model is required.
• Energy efficiency
• Large dispersion in G is required.

But, there are following problems

• Break energy problem
• Lower-energy spectra
• Energy transport
• Particle acceleration

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In order to justify the model

• There are some serious problems in the standard
  model.
• We want to justify the assumed physical
  situation the size, G, magnetic field etc.
• If electrons are accelerated, protons should be
  also accelerated!!

(see Asano Takahara 2003)
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Maximum Energy of UHECRs
Maximum energy of protons may be limited by The
following condition

• Larmor radius should be smaller than the size of
  the shocked region.
• The cooling time(Synchrotron) should be longer
  than the acceleration time scale.

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Physical Condition in a Shell
?RR/G2
R
Photons Luminosity L
In the comoving frame Energy Density
Magnetic Field
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Time Scales
Let us consider a proton of 1019eV
In the comoving frame,
Acceleration Time Scale
Dynamical Time Scale
Cooling Time Scale
GRBs can produce UHECRs!
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Ultra-high energy cosmic ray(UHECR)
If Up above 1019 eVUe, it can explain the
flux of UHECRs.
Waxman 1995
41044erg Mpc-3 yr-1
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Neutrino
The assumption UeUp is checked with neutrino
observations.
p??np ?pp0
p?µ ?µ
µ ?e ?µ ?e
Note Even if protons are accelerated, there are
cases that protons cool down via photo-pion
production.
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Esh1051erg, R1013cm
Asano 2005
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Esh1051erg, R1013cm
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Neutrino Spectra
Pion-decay time and cooling time-gt
l1010cm
High Energy cut-off ?l0.5 R Low Energy cut-off
?R
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More detailed simulation
E 1054erg, N1000,
G1000
R1013 cm
Magnetic Energy Density
UB0.1U
GRB photon field
n(e)?e-1 for 1 eVltelt1 keV
n(e)?e-2.2 for 1 keVltelt10 MeV
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Mesons
Asano Nagataki 2006
See also Ando Beacom
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Neutrino Spectra
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Detection number of neutrinos
GRB at 30Mpc 1km2-detector
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EUSO case
Neutrinos detected with EUSO may come from kaons!
gt1019eV detector
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GLAST Era

• Practically, it is very hard to observe neutrinos
  from each event.
• Future gamma-ray observations with GLAST may
  bring us information on accelerated protons.

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Physical Condition
In the standard model
But, there is possibilities of
So, we consider various cases without prejudice.
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Microphysics in Our Simulation

• Photo-pion production
• Pion-decay
• Muon-decay
• Synchrotron radiation from electron, positron,
  muon, pion, and proton
• Photon scattering (Inv. Compton) with electron,
  positron, muon, pion, and proton
• Electron-positron pair creation
• Synchrotron self-absorption

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Assumption

• Totally 1053erg burst
• Redshift z0.1
• Electron power-law index3 (2.5 for photon)
• ?e,m is chosen to be Ebreak300 keV

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UeUBUp
40 amplified by protons
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UeUBUp
GeV Observation will determine G!
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UeUBUp, G300
E1051erg x 100 shells R1015 cm
Inv. Compton dominates above GeV.
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UeUBUp, More Luminous Case
Target with Cherenkov Detectors
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Magnetic Field and Cascade
Strong magnetic field enhances the cascade
processes!
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Magnetic Field and GeV Photons
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Muon Synchrotron
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Proton Synchrotron
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Other Interesting Feature
Heating Effect due to Self absorption
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Other Interesting Feature 2
B250 G
tcoolgttdyn
Proton Synchrotron
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Conclusion

• Future observations in neutrinos and GeV photons
  will be important to determine the model
  parameter.
• If protons are accelerated sufficiently,
  characteristic feature, such as muon or proton
  synchrotron etc., may be observed.

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??????
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The standard Model
Lorents factor of the shock
Proton temperature
Electron Temperature
Number fraction of non-thermal electrons
Energy fraction of non-thermal electrons
Energy fraction of magnetic field
Average energy of non-thermal electrons
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f1 is the most efficient case.

• If f1, efficient gamma-ray production from the
  dissipated kinetic energy of outflows is
  realized.
• fltlt1 is natural, but there is huge amount of
  unobserved energy(EEobs/f) in this case.

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Compactness Problem
If gamma-rays are emitted isotropically, the
fireball becomes optically thick because of
electron-positron pairs created via photon-photon
collision.
?Inconsistent with obs.
We need a Lorentz factor more than
100
X-ray
In the comoving frame
No high energy photons
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Multiple Shells
Multiple shells emit independetly of each other
?Internal Shock Model
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Fermi Acceleration
v
Shocked Region
Magnetic Field
u
GRBs are also considered to be emission from
non-thermal electrons
Particle
Shock Front
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Degeneration of the parameters
Eichler Waxman ApJ 627, 861
If
Total Energy
Density of ISM
Observables are same as the case of f1.
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Kinematics
Shock propagation Blandford-McKee(1976)
Shell width
If E/n is constant, the kinematics is conserved.
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Spectrum
Energy Transport from protons to non-thermal
electrons
In case of f1
In case of flt1
is constant
The 1st in LHS is neglected ?
Magnetic Field
In order to keep the magnetic field
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Energy Efficiency
Collision of a rapid shell and a slow shell
Internal Energy
Energy Conservation
Momentum Conservation
If equal masses
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Energy Efficiency(2)
Efficiency
equal mass
If ?f0.057 ?f0.43
Large G-dispersion is required!
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Expected Break Energy
Synchrotron
so that
Break Energy may have large dispersion.
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Small variation of break energy
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In numerical simulations
Asano Kobayashi 2003
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Problems

• Fundamental physical processes
• Energy efficiency
• Break energy
• Spectra in the lower energy band

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Many soft bursts should be observed
Similar Gs of the two shells lead to a soft burst.
Asano Kobayashi 2003
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Each pulse is independent?
Borgonovo and Ryde(2000)
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Spectra in the lower energy band
Emission from cooled enectrons may dominate in
the lower energy band.
Synchrotron spectra cannot be flatter than
Theoretical Prediction
Limit from synch.-theory
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Observer???
?
(???
)
???Ultra-Rela (?gt100)???
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Typical Electron Energy
Number Density
Energy Density
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Shell????????
1/?
Observer
?????????
dT?T???????
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?gt100????????????
?
Photon
Observer
R
c?T
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???????????
????
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??????????
?????????
???????? ???????
Smith Epstein(1993)
Compactness?????
??????????
???????????
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?????????
???????
?????????
???????????????
???????Optical Depth
????
f?????????????????? f??????????????????
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??
GRB 990123
X-ray
Optical
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Jump Condition
Shell???L???M? shell???????????G? ?????????????
??
Shocked???????
?????????
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?????
???