Andreas Horneffer

1
Radboud University Nijmegen
Experimental
Results from LOPES, an Overview

• Andreas Horneffer
• for the LOPES Collaboration

2
Radio Emission from Air Showers

• Air showers emit short, intense radio pulses
• Radiation due to geomagnetic emission process
  e.g. geosynchrotron
• Coherent emission at low frequencies
• Measuring the radio emission from air showers
  could give several benefits
• Higher duty cycle than fluorescence telescopes
• Effective RFI suppression allows measuring in
  polluted (populated) areas
• Data integrated over the shower evolution, can be
  complementary to particle detectors
• High angular resolution possible

3
LOPES(LOFAR Prototype Station)

• Set up at and working together with
  KASCADE-Grande
• Frequency range of 40 80 MHz
• Triggered by KASCADE or Grande large event
  trigger
• 10 antennas in the first phase
• 30 antennas in second phase
• reconfigured for dual-polarization
• plus LOPESSTAR antennas

• Goals
• Develop techniques to measure the radio emission
  from air showers
• Determine the radiation mechanism of air showers
• Measure the properties of the radio emission from
  air showers
• Calibrate the radio data with theoretical and
  experimental values from an existing air shower
  array

4
First detection of CR radio pulse by LOPES

• Strong coherent radio pulse coincident with air
  shower
• Shows direct association of radio with air shower
  geometry
• All-sky radio-only mapping
• Imaging (AZ-EL) with time resolution of 12.5 ns
• Total duration is 200 ns
• No cleaning was performed, side lobes still
  visible
• Location of burst agrees with KASCADE location to
  within 0.5.

Falcke et al. (LOPES collaboration) 2005, Nature,
435, 313
5
Radio Pulse Height Parametrisation

• Comparison with KASCADE data
• leads to parameterization formula
• eEWA(B-cos(a))cos(?)exp(R/R0)
• (E/1017eV)? µV/m MHz
• With A111 B1.160.025
• R0236 81 ?0.950.04

E
Horneffer et al. (LOPES coll.) ICRC(2007) Merida
6
Lateral Behavior

• Investigate the lateral behavior by
• Statistical analysis of many events
• Analysis of single antennas in strong events

R0236 81
110 events
single event
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Lateral BehaviorFlat Events Simulations

• Simulations predict systematically smaller scale
  parameters
• R0,simlt100m
• Some events show a flat behavior with large R0
• no flat distributions obtained in simulations

S. Nehls, PhD-Thesis 2008 Uni Karlsruhe
8
Lateral BehaviorFlat Events Simulations

• Possible explanation flat inner region
• Needs further study!

S. Nehls, PhD-Thesis 2008 Uni Karlsruhe
9
Frequency Spectrum

• Spectrum of the radio pulse from two methods
• sub-band filtering
• Fourier-transform of single pulses
• Can be fit with a power law of slope -1
• No dependence on direction, energy or distance
  found
• Consistent with simulations

power law slope a-10.3
Nigl et al. (LOPES coll.) AA accepted
10
Thunderstorm Effects

• Measured clear radio excess during thunderstorms
• For Egt100 V/cm E-field force dominates B-field
• Fair weather E1 V/cm
• Thunderstorms E1 kV/cm
• Electric fields have two main effects depending
  on geometry
• Additional curvature of e
• Linear acceleration of e
• B-field effect dominates under normal conditions
• gt90 duty cycle possible

Thunderstorm events
control sample
perfect weather sample
Buitink et al. (LOPES coll.) AA 467(2007)385
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Polarization

• Some events show strong polarization
• In general
• Events from East or West have stronger NS
  component
• Events from North or South have stronger EW
  component

EW Component
NS Component
Isar et al. (LOPES coll.) ICRC(2007) Merida
12
Preparing the Future

• LOFAR
• High sensitivity
• Excellent calibration
• Radio_at_Auger
• Development of autonomous antennas
• Self triggering
• Simulations!!!

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Summary

• Radio signal depends on angle to geomagnetic
  field.
• Confirmation of geomagnetic emission process.
• Pulse height scales about linearly with primary
  energy.
• Confirmation of coherent emission.
• Pulse height scales with distance eexp(R/R0)
• Larger R0 value found than in simulations,
  flattening at the center?
• Frequency spectrum is a decreasing power law or
  exponential.
• Compatible with simulations
• Amplified radio signal during thunderstorms.
• Strong electric fields can influence the emission
  process.
• Polarization shows azimuthal dependence.
• Similar to simulations.
• Not shown
• LOPES is more sensitive to inclined air showers
  than KASCADE.
• The angular resolution of LOPES increases with
  primary energy.

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LOPES Collaboration
ASTRON, The Netherlands H. Butcher G. de
Bruyn C.M. de Vos G.W. Kant Y. Koopman H.J.
Pepping G. Schoonderbeek W. van Capellen S.
Wijnholds
Dept of Astrophysics, Nijmegen, The
Netherlands L. Bähren S. Buitink
H. Falcke J.R. Hörandel A. Horneffer J.
Kuijpers S. Lafèbre A. Nigl J. Petrovic K. Singh
Dipartimento di Fisica Generale dell'Universita,
Torino, Italy M. Bertaina A. Chiavassa F. Di
Pierro G. Navarra
Institut für Kernphysik, FZK, Germany W.D.
Apel J.C. Arteaga A.F. Badea K. Bekk J.
Blümer H. Bozdog K. Daumiller P. Doll R.
Engel M. Finger A. Haungs D. Heck T.
Huege P.G. Isar H.J. Mathes H.J. Mayer S.
Nehls J. Oehlschläger T. Pierog H. Rebel M.
Roth H. Schieler F. Schröder H. Ulrich A.
Weindl J. Wochele M. Wommer
Univ Wuppertal, Germany J. Auffenberg D.
Fuhrmann R. Glasstetter K.H. Kampert J.
Rautenberg
Universität Siegen, Germany M. Brüggemann P.
Buchholz C. Grupen D. Kickelbick Y. Kolotaev S.
Over W. Walkowiak
Max-Planck-Institut für Radio- astronomie, Bonn,
Germany P.L. Biermann J.A. Zensus
IPE, FZK, Germany T. Asch H. Gemmeke O.
Krömer M. Manewald L. Petzold A. Schmidt
Istituto di Fisica dello Spazio Interplanetario,
Torino, Italy E. Cantoni P.L. Ghia C.
Morello G.C. Trinchero
National Inst of Physics and Nuclear Engineering
Bucharest,Romania I.M. Brancus B. Mitrica M.
Petcu A. Saftoiu O. Sima G. Toma
Univ Karlsruhe, Germany F. Cossavella V. De
Souza M. Ender D. Kang K. Link M.
Ludwig M. Melissas N. Palmieri
Soltan Institute for Nuclear Studies, Lodz,
Poland P. Luczak J. Zabierowski
15
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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SimulationsExtraction of Xmax
Huege et al. (2008)
Lafebre et al. (2008), in prep.