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Photons and Neutrinos Originating from Accelerated Protons in GRBs

Photons and Neutrinos Originating from Accelerated Protons in GRBs. Katsuaki ASANO (National Astronomical Observatory of Japan). Collaborators: S.Inoue, S.Nagataki, F.Takahara. Abstract.

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Photons and Neutrinos Originating from Accelerated Protons in GRBs

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  1. Photons and Neutrinos Originating from Accelerated Protons in GRBs Katsuaki ASANO (National Astronomical Observatory of Japan) Collaborators: S.Inoue, S.Nagataki, F.Takahara

  2. Abstract • 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. We show results of our Monte Carlo Simulation.

  3. Gamma-Ray Burst

  4. Time Profile ΔT δT

  5. Energy Budget Shock Dissipated Energy ? Magnetic Field Acc. Electrons Acc. Protons Synchrotron Gamma-Rays

  6. Standard Picture of Electron Acceleration Thermal Electrons Electron number Non-thermal Energy

  7. 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

  8. Break Energy Break

  9. Observed Break Energy BATSE Data

  10. Problems in the Theory • Compactness problem＋Time Profile • Internal Shock Model is required. • Energy efficiency • Large dispersion in Γ is required. But, there are following problems; • Break energy problem • Lower-energy spectra • Energy transport • Particle acceleration

  11. 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, Γ, magnetic field etc. • If electrons are accelerated, protons should be also accelerated!! (see Asano & Takahara 2003)

  12. 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.

  13. Physical Condition in a Shell ΔR=R/Γ2 R Photons: Luminosity L In the comoving frame Energy Density: Magnetic Field:

  14. 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!

  15. Ultra-high energy cosmic ray（UHECR） If Up above 1019 eV～Ue, it can explain the flux of UHECRs. Waxman 1995 ４×１０44erg Mpc-3 yr-1

  16. Neutrino The assumption Ue～Up is checked with neutrino observations. ｐ＋γ→n+π＋ →p+π0 π＋→μ＋+νμ μ＋→e＋ + νμ+ νe Note: Even if protons are accelerated, there are cases that protons cool down via photo-pion production.

  17. Esh=1051erg, R=1013cm Asano 2005

  18. Esh=1051erg, R=1013cm

  19. Neutrino Spectra Pion-decay time and cooling time-> l=1010cm High Energy cut-off ∝l0.5 R Low Energy cut-off ∝R

  20. More detailed simulation E= 1054erg, N=1000, Γ=1000 R=1013 cm Magnetic Energy Density UB=0.1U GRB photon field n(ε)∝ε-1 for 1 eV<ε<1 keV n(ε)∝ε-2.2 for 1 keV<ε<10 MeV

  21. Mesons Asano & Nagataki 2006 See also Ando & Beacom

  22. Neutrino Spectra

  23. Detection number of neutrinos GRB at 30Mpc 1km2-detector

  24. 5 5 M u o n - d e c a y 4 4 3 3 P i o n - d e c a y 2 2 ] ) E K a o n - d e c a y ( 1 1 N 5 2 E 1 0 e r g x 1 0 0 [ 0 0 g G = 5 0 0 o l 1 4 R = 5 1 0 c m - 1 - 1 e e = 0 . 1 B e - 2 - 2 a t 1 G p c 5 2 b y 1 0 k m d e t e c t o r - 3 - 3 - 4 - 4 1 6 1 7 1 8 1 9 2 0 l o g E ( e V ) D t = 6 6 m s e c 5 3 L = 1 . 5 x 1 0 e r g / s EUSO case Neutrinos detected with EUSO may come from kaons! >1019eV detector

  25. 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.

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

  27. 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

  28. Assumption • Totally 1053erg burst • Redshift z=0.1 • Electron power-law index=3 (2.5 for photon) • γe,m is chosen to be Ebreak=300 keV

  29. Ue=UB=Up 40% amplified by protons

  30. Ue=UB=Up GeV Observation will determine Γ!

  31. Ue=UB=Up, Γ=300 E=1051erg x 100 shells R=1015 cm Inv. Compton dominates above GeV.

  32. Ue=UB=Up, More Luminous Case Target with Cherenkov Detectors

  33. Magnetic Field and Cascade Strong magnetic field enhances the cascade processes!

  34. Magnetic Field and GeV Photons

  35. Muon Synchrotron

  36. Proton Synchrotron

  37. Other Interesting Feature Heating Effect due to Self absorption

  38. Other Interesting Feature 2 B～250 G tcool>tdyn Proton Synchrotron

  39. 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.

  40. 予備スライド

  41. 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:

  42. ``f=1’’ is the most efficient case. • If f=1, efficient gamma-ray production from the dissipated kinetic energy of outflows is realized. • f<<1 is natural, but there is huge amount of unobserved energy（E=Eobs/f） in this case.

  43. 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

  44. Multiple Shells Multiple shells emit independetly of each other ⇒Internal Shock Model

  45. Fermi Acceleration v Shocked Region Magnetic Field u GRBs are also considered to be emission from non-thermal electrons… Particle Shock Front

  46. Degeneration of the parameters Eichler & Waxman ApJ 627, 861 If Total Energy Density of ISM Observables are same as the case of f=1.

  47. Kinematics Shock propagation: Blandford-McKee(1976) Shell width If E/n is constant, the kinematics is conserved.

  48. Spectrum Energy Transport from protons to non-thermal electrons In case of f=1: In case of f<1: is constant The 1st in LHS is neglected → Magnetic Field In order to keep the magnetic field

  49. Energy Efficiency Collision of a rapid shell and a slow shell Internal Energy Energy Conservation Momentum Conservation If equal masses

  50. Energy Efficiency(2) Efficiency equal mass If ⇒f=0.057 ⇒f=0.43 Large Γ-dispersion is required!

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