Propagation of UHE protons in magnetized large scale structure

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Propagation of UHE protons in magnetized large
scale structure
Santabrata Das
ARCSEC, Sejong University, South Korea.

• Collaborators
• Heysung Kang, PNU, Korea.
• Dongsu. Ryu, CNU, Korea.
• Jungyeon. Cho, CNU, Korea.

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Introduction

• Earths atmosphere is continuously bombarded by
  extremely high energetic particles.
• Such particles strikes every 100 sq.km/yr and
  form the tail of the cosmic-ray spectrum that
  extends from 1Gev to beyond 100EeV.
• We know little about them, in particular, we do
  not understand clearly how and where these
  particles gain their remarkable energies.

• They may be the evidence of unknown physics or
  of exotic particles formed in the early universe.

• They are possibly the only samples of
  extragalactic materials that can be detect
  directly.

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Observed energy spectrum of Cosmic Rays
Nagano, M. and Watson, A. A., 2000, Rev. Mod.
Phys., 72, 689
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Enigma of UHECRs
Gyroradius

• A cutoff in spectrum around 50 EeV is expected
  due to the interaction of particles with CMB
  photons (GZK limit).
• Observations establish particles with E gt 50EeV.
• This follows a nearby sources on cosmological
  scale.
• No nearby astronomical source have yet been
  identified.

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Composition of UHECRs

• Experimental studies of extended air shower
  establish the fact in favour of light composition
  above 10 EeV (Abbasi et al. 2005). This are in
  very good agreement with the HiRes, Yakutsk,
  Haverah Park data (Ave, M., et al, Astropart.
  Phys., 2003, 19, 47 Abu-Zaayad, T., et al,
  PRL., 2005, 84. 4276 Glushkov, A. V., et al,
  JETP Lett., 2000, 71, 97).
• UHECR composition is dominated by proton,
  although a mixed composition dominated by heavier
  nuclei cannot be ruled out.

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Origin of UHECRs

• UHECR sources need to satisfy few conditions
• Source must be strongly luminous and powerful.
• It must accelerate particles above E_max gt 1000
  EeV.

Astrophysical Sources

• Active Galactic Nuclei
• Gamma Ray Bursts
• Cosmological Shocks
• Etc.

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Extragalactic magnetic fields

• The strength and morphology of the
  intergalactic magnetic fields remain largely
  unknown as it is intrinsically difficult to
  observe. So far, direct evidence for the presence
  of the EGMFs has been found only in galaxy
  clusters.
• Geometry of cosmic magnetic field (special
  distribution of field strength and its
  orientation) is strongly correlated with large
  scale non-linear structures of the universe. This
  suggests, the field strength increases with the
  matter density.

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Numerical Simulation of large scale structure of
the universe
L cold dark matter cosmology ?L 0.73, ?DM
0.27, ?gas 0.043, h0.7, n 1, ?8
0.8 Computational box (100 h-1 Mpc)3
grid-based Eulerian TVD code.
(Ryu, Kang et al 2003, 2005)
6 sets of different realizations of initial
conditions are used.
EGMF model (Bx, By, Bz) are obtained from 1.
Passively evolving B fields in the simulations
? directional information
2. Vorticity of flows ? magnitude of B
fields (based on turbulent dynamo)
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Turbulent Dynamo model

• Magnetic field is assumed to result from the
  turbulent motion of the intergalactic gas.
• EGMFs are computed directly by equating magnetic
  energy to the suitable fraction of turbulent
  energy of intergalactic gas.

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Magnetic field strength in large scale structure
of the universe
Clusters
Filaments
Sheets
Voids

• inside clusters, B a few mG
• around clusters (T gt 107 K), B 0.1 mG
• in filaments (105 K lt T lt 107 K), B 10 nG
• in sheets (104 K lt T lt 105 K), B 10-10 G
• in voids (T lt 104 K), B 10-12 G

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2-D cuts of baryonic density EGMFs
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CR sources and observers

• CR Sources
• AGNs inside galaxy cluster with kT gt 1.0 keV.
• 20-30 sources in the simulated volume with source
  density
• Mean separation
• Most massive cluster with

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CR sources and Observers

• Observer locations
• Groups of galaxies with 0.05keV lt kT lt 0.5 keV.
• 1000 1300 observers in the simulated volume.
• Groups along filaments with

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Source-Observer locations inside Simulation Volume
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CR injection propagation through magnetized
universe

• CR injection
• for
• 30000 protons launched into random direction
  from sources.

• CR propagation
• Solve the equation of motion.
• B field our turbulent dynamo model.

Energy losses

• Pair-production

• Pion production

100EeV proton loses 1/e of its energy in 140 Mpc
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CR Injection propagation through magnetized
universe

• CR observation
• Passage within the observer sphere with
• Arrival direction (q) deflection angle from
  source position.
• Time delay relative to the rectilinear
  propagation.
• Continue its journey until proton loses energy
  down to 10EeV.
• Multiple visits observed events.

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Particle trajectories in EGMFs

• Random injection.
• 100h-1Mpc spatial distance propagation.
• Energy loss considered.

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Particle trajectories in EGMFs

• Random injection.
• 100h-1Mpc spatial distance propagation.
• Energy loss considered.

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Particle trajectories in EGMFs

• Random injection.
• 100h-1Mpc spatial distance propagation.
• Energy loss considered.

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Particle trajectories in EGMFs

• Random injection.
• 100h-1Mpc spatial distance propagation.
• Energy loss considered.

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Distribution of deflection angles
g 2.7
E gt 50 EeV
Kang, et al., ICRC, 2007
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Distribution of UHECR detection energy E and
deflection angle
g 2.7
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Distribution of time delay
g 2.7
E gt 10 EeV
E gt 100 EeV
Kang, et al., ICRC, 2007
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Distribution of UHECR detection energy E and Time
delay
g 2.7
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Energy spectrum of observed protons
Log E (eV)
Kang, et al., ICRC, 2007
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Summary

• Below GZK energy, the deflection angles and time
  delay are substantial.
• Around 20 of super-GZK events are expected to
  arrive at Earth within TWO degree.
• UHE charged particle astronomy may be possible
  for E gt 100 EeV.
• Predicted UHE proton spectrum with g 2.4-2.7
  fits HiRes data and exhibits the GZK cutoff.

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Thank you