1. The LOFAR Cosmic Ray KSP
Heino Falcke
LOFAR International Project Scientist Radboud University, Nijmegen ASTRON, Dwingeloo
+ LOFAR CR KSP

2. LOFAR CKP: Main Motivation
Exploring the sub-second transient radio sky:
Extensive Air showers as guaranteed signal
Radio flashes from the moon (UHECR and other?)
Identify and understand other sporadic signals (“RFI”, lightning, SETI, astrophysical sub-ms pulses with TKP)
Develop the techniques to work on raw time series data (transient buffer board & tied-array beam) in near field and far-field.

3. Astroparticle Physics: Radio Detection of Particles
Cosmic Rays in atmosphere:
Geosynchrotron emission ( MHz)
Radio fluorescence and Bremsstrahlung (~GHz)
Radar reflection signals (any?)
VLF emission, process unclear (<1 MHz)
Neutrinos and cosmic rays in solids: Cherenkov emission (100 MHz - 2 GHz)
polar ice cap (balloon or satellite)
inclined neutrinos through earth crust (radio array)
CRs and Neutrinos hitting the moon (telescope)

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 eV
Interaction of UHECRs with cosmic microwave background (“GZK cut-off”)?
UHECRs are extragalactic
Auger 2007, ICRC divided by E-3
The spectral index obtained is =2.62±0.03(stat)±0.02(sys). The system-
atic error is given by the error on the calibration curve in [5]. The number of events
expected from such a single power-law flux
above eV and 1020 eV are 132±9 and
30±2.5 respectively whereas we observe only
51 events and 2 events.
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”!
1set until May 24: 12/15 correlate
2ns set until May 24- August: 8/12 correlate (2.7 expected)
For combined set: 20 out of 27 cosmic rays events
236 correlate with at least one of the 442 selected AGN (292 in the eld of view
237 of the Observatory), while only 5.6 are expected on average to do so if the
238 ux were isotropic (p = 0:21)
µG B-fields and kpc scales needed
AUGER Collaboration (2007), Science
9. Nov. (2007)

7. 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)

8. LOFAR Moon experiment
Detectability of super-GZK cosmic rays and neutrinos hitting the moon

9. What are UHECRs made of? Current 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

10. Coherent Geosynchrotron Radio Pulses in Earth Atmosphere
Earth B-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 front e± ~50 MeV
Geo- synchrotron
coherent E-Field
Falcke & Gorham (2003), Huege & Falcke (2004,2005) Tim Huege, PhD Thesis 2005 (MPIfR+Univ Bonn

11. Radio CR Simulation Results: Extraction of Energy & Nmax
Huege et al. (in preparation)
Shower-to-Shower fluctuation is only 5%!

12. Radio Pulse Shape: Imprint of Shower Evolution
Tim Huege et al. (2007)
|E| (µV/m)
t (ns)

13. Extraction of Composition and Xmax from Curvature
Huege et al. (2008)
Lafebre et al. (2008), PhD

14. 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

15. Experimental Methods
UHEP – in-beam triggered radio observations of the moon
VHECR – antenna-based triggered detections in atmosphere
Data from all station for bright events
Search for isotropic signals, passive radar
Data only from triggering stations
HECR – in-beam triggered detection of CRs
Sub-Second Transients:
Monitoring of radio noise (lightning, RFI, Jupiter bursts, etc.)

16. Experimental Realization: Transient Buffer Board
© ASTRON

17. Transient Buffering Local Control Unit G. trigger External trigger

18. Incoherent Station-Beam
Beam Forming
(Tied) Array-Beam
Station-Beam
Incoherent Station-Beam
Antenna-Beam

19. Phased Array Beam Steering
LOFAR low-band element receives radiation from all directions.
Phased Arrays have a virtual steerable “focal surface” which can be adapted “at will”.
Buffering raw-data in each antenna allows offline beam steering.
Normal far-field imaging is just inclining a plane.

20. Phased Array Beam Steering
Curving the virtual “focal surface” allows near-field imaging.
Offline processing allows one to scan an entire volume at all frequencies and time ranges.
Search for fast and unpredictable bursts.
Distinguish cosmic from terrestrial effects.

21. 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

22. 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)

23. Observing Time UHEP/Moon: VHECR mode A: VHECR mode B: HECR:
Initially 1 month of accumulated observing time under good ionospheric conditions
sensitivity that is orders of magnitude better than the sensitivity of existing experiments
Extend to three months to reach UHECR-extrapolation and show GZK cut-off
VHECR mode A:
About 1 month of accumulated observing time
1000 good events.
VHECR mode B:
Continuous observations, and at least 1/3 of the time with the low-band antennas.
HECR:
based on availability of resources
TS-mode: triggered by dynamic spectrum – indicating unusual radio conditions (e.g. lightning)
One-Second All Sky Survey (OSASS) – Take several full-buffer dumps and image entire sky (Flux calibration and transient search)
Map tied array data (Calibration for Moon and transient search)

24. Cosmic Rays in the Radio
νMoon
S. Lafebre

25. Summary
Technical goal of CKP: Tempo-spatial properties of sub-second radio flares
UHECRs:
Understand the radio emission properties of extensive airshowers in great detail
Precise composition analysis of CRs (“What are they?”)
Precise localization of UHECRs (“Where do they come from”?)
Closely interact with AUGER observatory MAXIMA).
Improve limits on super-GZK CRs to meaningful values.
Explore other methods (passive radar, isotropic emission?)
Be open for other and new fast radio phenomena:
Lightning investigation (with KNMI – Dutch Meteorological Inst.)
Lunar radio flares from meteorite impacts
Search for astrophysical sub-second radio bursts: One-Second All-Sky Survey (OSASS)
Transient SETI (here rely on open-source/open-data model)

26. 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 ...