Radio Detection of UltraHigh Energy Cosmic Rays

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Radio Detection of Ultra-High Energy Cosmic Rays
Here Theory of Radio Air Shower Detection For
rest see subsequent talks by Dallier Buitink

• Heino Falcke
• LOFAR International Project ScientistRadboud
  University, NijmegenASTRON, Dwingeloo
• LOPES LOFAR CR Collaborations

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Radio Images of Cosmic Accelerators
Cygnus A
Cas A
NRAO/AUI
Fornax A
1.4 , 5, 8.4 GHz
... is there anything else that radio astronomy
can offer?
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Cosmic Ray Energy Spectrum

• Cosmic rays are very energetic particles (vc)
  accelerated in the cosmos
• The differential Cosmic Ray spectrum is described
  by an almost universal power law with a E-2.75
  decline.
• Low-energy cosmic rays can be directly measured.
• High-energy cosmic rays are measured through
  their air showers.

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Randomization of charged particles

• Charged particles are randomized by
• the interstellar magnetic field in the Milky Way
  (around the knee)
• the intergalactic magnetic field at the highest
  energies
• Projected view of 20 trajectories of proton
  primaries emanating from a point source for
  several energies. Trajectories are plotted until
  they reach a physical distance from the source of
  40Mpc.
• At 1020 eV one could perhaps do cosmic ray
  astronomy in the nearby universe.

1EeV 1018 eV
Cronin (2004)
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What we (dont) know about UHECRs

• We know
• their energies (up to 1020 eV).
• their overall energy spectrum
• We dont know
• where they are produced
• how they are produced
• what they are made off
• exact shape of the energy spectrum

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Auger UHECR Spectrum

• Reliable energy spectrum up to gt1020 eV from
  surface detectors (SD)
• Evidence for a suppresion above 1019.6 eV
• Interaction of UHECRs with cosmic microwave
  background (GZK cut-off)?
• UHECRs are extragalactic

Auger 2007, ICRCdivided by E-3
30 expected for E-2.6, 2 seen
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Auger Clustering of UHECRs
New data confirms correlation with AGN
clustering. Chance probability 2 10-3 The
beginning of charged particle astronomy!
AUGER Collaboration (2007), Science
9. Nov. (2007)
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Current Detection MethodsCan we do even better?

• Fluorescence
• Sees entire shower evolution
• Oversees large volume
• Only works during clear, moonless nights (10
  duty cycle)
• Light absorption by aerosols
• Cherenkov particle detectors
• Works 100 of time
• Well studied
• Only sees particles reaching ground
• Expensive cumbersome

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Current Detection Methods
Longitudinal Shower Profile

• Fluorescence
• Sees entire shower evolution
• Oversees large volume
• Only works during clear, moonless nights (10
  duty cycle)
• Light absorption by aerosols
• Cherenkov particle detectors
• Works 100 of time
• Well studied
• Only sees particles reaching ground
• Local detection only

Depth in Atmosphere
Particle Number
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Advantages of Radio Emission from Air Showers

• Cheap detectors
• High duty cycle (24 hours/day)
• Low attenuation, good calibratability (also
  distant and inclined showers)
• Bolometric, i.e. good energy measurement
  (integral over shower evolution)
• Interferometry gives precise directions
• Complementarity with SD gives composition
• But, does it work?
• Problems before 2001
• No theoretical understanding
• No experimental understanding since 1974
• .

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Radio Emission from Air Showers A Very Brief
History
Oscilloscope traces of CR radio pulses

• Initial motivation through prediction of
  Cherenkov-like radio emission process (Askaryan
  1962).
• Radio pulse discovery at Jodrell Bank at 44 MHz
  (Jelley et al. 1965).
• Various experiments around the world but problems
  with data acquisition (oscilloscopes!) and
  interference.
• Death and resurrection of radio detection
• ICRC 1975, Watson radio obituary it is clear
  that experimental work on radio signals has been
  terminated elsewhere'.
• ICRC 1977, Harold 'The logical decision is to
  abandon radio emission as a tool in air shower
  investigations
• ICRC 2007, plenary lecture on Radio Detection of
  UHECRs and many other contributions
• 2001 Peter Biermann points out potential
  relevance for LOFAR radio telescope

Jelley et al. (1965)
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Coherent Geosynchrotron Radio Pulses in Earth
Atmosphere
EarthB-Field0.3 G

• UHECRs produce particle showers in atmosphere
• Shower front is 2-3 m thick wavelength at 100
  MHz
• e emit synchrotron in geomagnetic field
• Emission from all e (Ne) add up coherently
• Radio power grows quadratically with Ne
• EtotalNeEe
• Power ? Ee2 ? Ne2
• GJy flares on 20 ns scales

shower fronte 50 MeV
Geo-synchrotron
coherentE-Field
Falcke Gorham (2003), Huege Falcke
(2004,2005) Tim Huege, PhD Thesis 2005
(MPIfRUniv Bonn
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Different Approaches
Buitink 2008, PhD Nijmegen, in prep.
Radiation Formulae for transversal acceleration
or current
GeosynchrotronFalcke Gorham, Huege Falcke
Particle-based
Current-based
Kahn Lerche, Werner Scholten
The difference lies in the approximation of the
current
Here no emission from shower maximum dN/dt0!
Falcke Gorham, Huege Falcke
Kahn Lerche, Werner Scholten
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Simulation design
T. Huege REAS2 radio code

• Monte Carlo simulation
• Calculate electric field from a single
  particleat different positions on the ground
• Add pulses from many electrons and positrons
• Separation of particle and radiation codes
• Intermediate step saves calculation time
• Different sources of particle distributionsParam
  eterizations,Corsika, Seneca,

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Frequency spectrum
20 m
Huege et al. (2005)
140 m
260 m
E (µV/m/MHz)
380 m
500 m
v (MHz)
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Corsika histograms
S. Lafebre LOFAR air shower library on BlueGene
Supercomputer

• Corsika simulations with 50 slicesat equidistant
  shower depths
• Record e/e characteristics
• Energy
• Lateral distance
• Arrival time
• Momentum angles

20 g/cm2
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Extraction of Energy Nmax
Huege et al. (in preparation)
Shower-to-Shower fluctuation is only 5.
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Pulse shape
Raw radio pulse of a 1019 eV proton shower as
seen north of the shower core
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Contributions in terms of energy
Huege et al. (2007)
E (µV/m)
t (ns)
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Contributions in terms of depth
Huege et al. (2007)
E (µV/m)
t (ns)
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Curvature
Lafebre et al. (2008), in prep.
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Extraction of Xmax
Huege et al. (2008)
Lafebre et al. (2008), in prep.
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LOPESLOFAR Prototype Station
250 particle detector huts
30 Radio Antennas40-80 MHzraw RF data buffer
LOPES Collaboration MPIfR Bonn, ASTRON, FZ
Karlsruhe, RU Nijmegen, KASCADE Grande
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Imaging of CR radio pulses with LOPES
A. Nigl 2007, PhD
Horneffer, LOPES30 event
See also Falcke et al. (LOPES collaboration)
2005, Nature, 435, 313
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Cross Calibration of LOPES10 and KASCADE
UHECR Particle Energy
B-field
Distance
Horneffer-Formula 2006/2007
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Nanosecond Radio Imaging in 3D
Actual 3D radio mapping of a CR burst No
simulation!

• Off-line correlation of radio waves captured in
  buffer memory
• We can map out a 5D image cube
• 3D space
• 2D frequency time
• Image shows brightest part of a radio airshower
  in a 3D volume at ttmax and all freq.

Bähren, Horneffer, Falcke et al. (RU Nijmegen)
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Positional Accuracy
Particle Detectors vs. Radio Antennas
Interferometry gives excellent position
information! The radio emission from normal
showers is directly associated with the particle
shower within our beamsize.
Air showers are amplified and modified in
thunderstorm electric field!
averagebeamsize
linear improvement with SNR
Nigl 2007, PhD, RU Nijmegen
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Thunderstorm Events

• CORSIKA simulations with thunderstorm electric
  fields
• Electrons and positrons are accelerated and
  deflected (Electron rain)
• This can lead to increased radio emission
• The shower is modified in thunderstorms not the
  radio emission
• Does this have relevance for CR lightning
  initiation?

CORSIKA air shower simulation with thunderstorm
electric fields
Vertical E-Field
Positron Rain
Buitink et al. (LOPES coll.) 2007, (ICRC)
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Thunderstorm Events

• CORSIKA simulations with thunderstorm electric
  fields
• Electrons and positrons are accelerated and
  deflected (Electron rain)
• This can lead to increased radio emission
• The shower is modified in thunderstorms not the
  radio emission
• Does this have relevance for CR lightning
  initiation?

CORSIKA air shower simulation with thunderstorm
electric fields
Buitink et al. (LOPES coll.) 2007, (ICRC)
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CRs with LOFAR (100xLOPES)
Every dipole has a 1s Transient Buffer storing
the full electro-magnetic wave information
(all-sky, all-frequency)!
LOFAR 900 dipoles will see one shower
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LOFAR advantages

• 900 dual-polarized dipoles within 2x2 km
• 900 dual-polarized dipoles out to 50 km
• Antennas are grouped in station fields and are
  synchronized and triggered centrally
• Antennas can be combined later to see radio out
  to large distances (SNR increase by factor 100
  over LOPES antenna)!
• Precise shower front and hence accurate
  composition direction
• Excellent energy resolution
• Limited to energies around a few 1015-18 eV

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Auger Expansion (MAXIMA) advantages

• 20 km2 dual polarized test array (100 antennas)
• Gives high duty cycle for hybrid events (SD)
• Combination with surface detectors and
  fluorescence telescopes will allow triple
  coincidences (tri-brid events)
• Cross-calibration between methods
• Eventually will need complete Auger with radio
  antennas
• Accurate determination of all UHECR parameters
  with 100 hybrid events
• LOFAR Radio_at_Auger Beginning of High-Precision
  UHECR Astrophysics

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Ultra-High Energy (Super-GZK) Neutrino Detections

• Ultra-high energy particle showers hitting the
  moon produce radio Cherenkov emission (Zas,
  Gorham, ).
• This provides the largest and cleanest particle
  detector available for direct detections at the
  very highest energies.
• In the forward direction (Cherenkov cone) the
  maximum of the emission is in the GHz range.
• Current Experiments
• ANITA
• GLUE
• FORTE
• RICE

radio from neutrinos hitting the moon
from Gorham et al. (2000)
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Cosmic Rays in the Radio
?Moon
S. Lafebre
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Conclusions

• Challenges for UHECRs in the future
• getting better composition and energy analysis
  (to reduce uncertainty in GZK cut-off
  determination estimate)
• Get even better directional information to
  improve clustering analysis identify sources
• Get to the super-GZK particles
• Become bigger, better, cheaper, smarter
• Radio emission of UHECR should give
• excellent energy resolution (5?)
• precise 3D localization and imaging (0.1)
• Composition from shower front and pulse shape
• high duty cycle
• With Auger charged particle astronomy has
  begun GZK cutoff, AGN correlation,
• With Radio high-precision particle astronomy will
  begin
• But this requires still a significant
  experimental effort ...