Radio Detection of Ultra-High Energy Cosmic Rays

1. 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

2. 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?

3. Cosmic Ray Energy Spectrum • Cosmic rays are very energetic particles (v~c) 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.

4. What we (don’t) know about UHECRs • We know: • their energies (up to 1020 eV). • their overall energy spectrum • We don’t know: • where they are produced • how they are produced • what they are made off • exact shape of the energy spectrum

5. Auger: UHECR Spectrum • Reliable energy spectrum up to >1020 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

6. 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)

7. 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

8. 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

9. 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 .

10. Coherent Geosynchrotron Radio Pulses in Earth Atmosphere EarthB-Field~0.3 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 • Etotal=Ne*Ee • 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 (MPIfR+Univ Bonn

11. Different Approaches Buitink 2008, PhD Nijmegen, in prep. Radiation Formulae for transversal acceleration or current Geosynchrotron:Falcke & 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/dt=0! Falcke & Gorham, Huege & Falcke Kahn & Lerche, Werner & Scholten

12. 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 distributions:Parameterizations,Corsika, Seneca, …

13. Frequency spectrum 20 m Huege et al. (2005) 140 m 260 m |E| (µV/m/MHz) 380 m 500 m v (MHz)

14. 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

15. Extraction of Energy & Nmax Huege et al. (in preparation) Shower-to-Shower fluctuation is only 5%.

16. Pulse shape Raw radio pulse of a 1019 eV proton shower as seen north of the shower core

17. Contributions in terms of energy Huege et al. (2007) |E| (µV/m) t (ns)

18. Contributions in terms of depth Huege et al. (2007) |E| (µV/m) t (ns)

19. Curvature Lafebre et al. (2008), in prep.

20. Extraction of Xmax Huege et al. (2008) Lafebre et al. (2008), in prep.

21. LOPES:LOFAR 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

22. 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

23. Cross Calibration of LOPES10 and KASCADE UHECR Particle Energy B-field Distance Horneffer-Formula 2006/2007

24. 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 t=tmax and all freq. Bähren, Horneffer, Falcke et al. (RU Nijmegen)

25. 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

26. 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)

27. 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)

28. CRs with LOFAR (100xLOPES): Every dipole has a 1s “Transient Buffer” storing the full electro-magnetic wave information (all-sky, all-frequency)! Antenna fields 2 x 2 km2 core area LOFAR: ~900 dipoles will see one shower

29. 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

30. 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@Auger: Beginning of High-Precision UHECR Astrophysics

31. 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)

32. Cosmic Rays in the Radio νMoon S. Lafebre

33. 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 ...