LUNASKA: Towards UHE Particle Astronomy with the Moon and Radio Telescopes

1. LUNASKA LUNASKA: Towards UHE Particle Astronomy with the Moon and Radio Telescopes Clancy W. James, University of Adelaide (Supervisors: R. Protheroe, R. Ekers)

2. What are these cosmic accelerators? Is there a cut-off to the spectrum? GZK Neutrinos • UHE protons interact with CMBR (GZK Interactions) • Neutrino secondaries ?

3. proton gamma neutrino The ‘Ideal Messengers’ Neutrinos: • Travel in strait lines – source identification! • Rarely interact – observed flux = source flux! * B-Fields ?

4. Auger: CR-AGN Correlation Science 318 (2007) • CR can be used for astronomy • More statistics needed

5. The Askaryan Effect 1. UHE particle interaction 2. Cascade of secondaries 3. Negative charge excess 4. Coherent Cherenkov radiation 5. Dense medium: Coherency in GHz regime. O(3m) O(10cm)

6. The Lunar Cherenkov Technique neutrino Parkes Kalyazin Goldstone WSRT ATCA radio waves (coherent Cherenkov radiation) cosmic ray shower SKA “A radio method to determine the origin of the highest-energy neutrinos and cosmic rays." AGN? GRB? DM? R. Ekers

7. Predicted Observation Coherent Cherenkov Radiation Spectrum Signature • Nanosecond-duration pulses • These are transients! • Must be distinguished against a thermal and RFI background • This requires non-standard methods! Spectrum • Broadband (peak < 5 GHz) • 100% linearly polarised • Coherent emission process • Scaling in the coherent regime: • Voltage V: • Received power:

8. Lunar Radio: Parkes 1995 (10 hrs) Goldstone 2000-2003 (120 hrs) Kalyazin ~(2000?)-2004 (~35 hrs) ATCA 2006- (~40 hrs) Westerbork 2007- (24 hrs) Other experiments: FORTE (satelite) ANITA (Antarctic balloon) Auger (hybrid CR) Experimental History NO UHE Neutrinos Observed. How can we improve?

9. SKA – the Square Kilometre Array • A giant next-generation radio array to be built in either western Australia or southern Africa by 2020. • How can we use this to detect UHE particles? • What can we do in the meantime?

10. Collaboration R. Protheroe C. James R. McFadden R. Ekers P. Roberts C. Phillips With credits to: D. Jones, R. Crocker, S. Tingay, R. Bhat, J. Alvarez-Muniz, J. Bray A theoretical and experimental project for UHE neutrino astrophysics using a giant radio observatory. Use ATCA (Australia Telescope Compact Array) as an SKA test-bed. Simulate detection to improve sensitivity. “Lunar UHE Neutrino Astrophysics with the Square Kilometre Array” LUNASKA

11. Triggering η sec time resolution Data rates too high for baseband recording: we must search for pulses in real time This requires fast (η sec) trigger logic Sensitivity Coherent addition of signals from: A large collection area A wide bandwidth Large antenna will only see a fraction of the Moon – use many small dishes or PAF Significant beamforming requirements RFI Discrimination Some terrestrial RFI still appears as a η sec pulse car engines internal electronics unknown sources??? How to determine real events with a few nanoseconds of data? Ionospheric Dispersion The Earth’s ionosphere smears our signals & destroys the coherency This drastically reduces sensitivity We must correct for this in real time! Experimental Hurdles

12. Ionospheric Dispersion • Ionospheric dispersion destroys the characteristic coherency of the pulses • The effect is worse during the day, at low frequencies, and at solar cycle max Night, solar cycle min Day, solar cycle max High frequencies Low frequencies

13. Dedispersion Ultimate Goal: • We must measure and correct for ionospheric dispersion in real time. • Must be performed coherently across the band • Both steps are currently impossible. Final Technique: ‘the McFadden Method’ • Lunar thermal emission few % polarised at limb • This gets rotated in the Earth’s B-Field • Measure Faraday rotation • Model Earth’s B-field • Derive dispersion measure • We can use our source as our calibrator! B

14. A Hardware Implementation Design an analogue dedispersion filter set for our 1.2-1.8 GHz band Set for typical night-time dispersion (5.5 ns inc slant angle) Results We can use the dispersion to discriminate against terrestrial RFI Q: Could this have lunar origin? Predictions – from a 3am Analysis True Event? Satelite-bounce? Terrestrial Impulse? Dedispersion Observed Trigger

15. Timing Callibration: 3C273 • Point antennas at a point source (bright quasar) • Trigger off the noise cal pulse • Correlate resulting buffers between antennas.

16. Observations 3 days May 5-7th 2007 (completed) Primarily hardware testing 5 hrs stable configuration ‘Targeted’ galactic centre region Next run: Feb 26-28th 2008 Method 3 Antennas 1.2-1.8 GHz bandwidth 8-bit sampling Dual linear polarisation Independent Triggers (3x10 Hz) – at the time only millisecond relative timing was possible 1 μ sec (2048 sample) buffers recorded Data Reduction 120,000 candidates ~300 remain after dumb coincidence and RFI cuts Polarisation + ‘smart’ RFI cuts: 4 remain (expect ~6 thermal events) 2008: η sec timing would give 4/1012 chance of a false detection 2007 Observations NO PULSES DETECTED Instantaneous Aperture

17. Maximising Sensitivity Do we point at the centre of the Moon or at the limb? What frequency to use? What dish size? Directionality To which directions are we most sensitive? What parts of the sky currently have low limits? Cosmic Rays These generate showers very similar to that of neutrinos. Are the differences important? Reconstruction If we see a signal, what was the primary particle Type (CR or nu)? Energy? Arrival direction? Surface Roughness The Moon is rough on all size scales: large (hills, craters) and small (rocks & perturbations ~ 1 wavelength) These effects are currently not well modelled. Theoretical Hurdles

18. Limb Brightening • Various geometrical effects mean we expect more signals from the lunar limb (limb brightening). • The effect is greatest at: • Low energies • High frequencies PAFs or Multibeams Small dishes (large beams)

19. Instantaneous Sensitivity • Relative instantaneous sensitivity of Parkes antenna to 10^22 eV neutrinos for (left) limb-pointing and (right) centre-pointing. • Peak sensitivity to a point source is 20 times the solid-angle averaged value. Conclusion: we can make targeted observations!

20. Goldstone Lunar UHE neutrino Experiment (GLUE) (plotted) Kalyazin observations (likely to be northern) ANITA & ANITA-lite (confined w/in yellow band) FORTE (threshold 10^23 eV, similar coverage to ANITA) Current UHE Limits 10^22 eV Target Here

21. UHE Particle Astronomy Neutrinos & the highest energy cosmic rays travel in straight lines Arrival directions correlate with the source. How do we determine this? Assumptions: 100-300 MHz Observations Resolution: 5” polarisation Remaining Uncertainty Lunar surface roughness Width of Cherenkov cone Determining Arrival Direction Instantaneous aperture is large Apparent signal exit position correlates with particle arrival direction. Polarisation aligns with the shower axis. Signal Exit Position Instantaneous Aperture Polarisation Reconstructing Arrival Direction This is a simplistic procedure

22. UHE neutrino cross-section Small scale surface roughness SKA Sensitivity to UHE Neutrinos Uncertainties: • Depth of the regolith

23. SKA Sensitivity to UHE CR Uncertainties: • Large-scale surface roughness • ‘formation zone’ effects

24. Summary • Lunar Cherenkov Technique provides a method to detect the highest energy neutrinos and cosmic rays with ground-based radio-telescopes • The SKA could use this technique to be a powerful instrument for UHE particle astronomy • Cosmic Ray Detection: ~one Auger-year in one night • Even a single detection of an UHE neutrino would open a new era in astronomy and become a key SKA science driver • Ongoing observations w ATCA – keep your fingers crossed!