The Lunar Cherenkov Technique – From Parkes Onwards

1. LUNASKA LUNASKA The Lunar Cherenkov Technique – From Parkes Onwards UHE Neutrino Flux Limits - From Parkes Onwards The LUNAKSA Collaboration • R. Protheroe • C. James • R. Ekers • P. Roberts • C. Phillips • R. McFadden • S. Tingay • R. Bhat • J. Alvarez-Muniz • T. Stanev “Lunar UHE Neutrino Physics with the Square Kilometre Array”

2. Outline • Part 1: Simulation results from Parkes • The Parkes Lunar Cherenkov experiment • Simulation results on directional sensitivity • Directional dependence of current limits • Part 2: UHE Particle Astronomy • Resolution of arrival direction • Spectral information • The Square Kilometre Array (SKA) The Lunar Cherenkov Technique: From Parkes Onwards

3. The Parkes Lunar Cherenkov Experiment • Overview • Hankins et al 1996 • 1st use of the Lunar Cherenkov technique • Used Parkes 64m antenna • No aperture/limits calculated • Observations • Jan 18th-19th 1995 • 10.5 hours on-line • Only 2 hours at the limb • Signal Detection • 1.425 GHz RCP & LCP data • 500 MHz bandwidth recorded • Trigger from 2x100 MHz sub-bands • RFI discrimination: ionospheric delay The Lunar Cherenkov Technique: From Parkes Onwards

4. Parkes – Aperture and Limit Parkes UHE Neutrino Isotropic Flux Limit: • Instantaneous aperture comparable to GLUE, Kalyazin • Short observation time = weak constraints • Since surpassed by other experiments • What can we learn? APERTURE LIMIT C. W. James et al., 2007 The Lunar Cherenkov Technique: From Parkes Onwards

5. Directional Aperture Definition • Effective isotropic aperture (km^2-sr) usually quoted • But is calculated from: where is the directional aperture to neutrinos at coordinates (relative to the Moon) Origin of Directional Dependence • Lunar shadowing • Cherenkov geometry • Refraction and surface roughness • Beam pointing Beam centre The Lunar Cherenkov Technique: From Parkes Onwards

6. Parkes Directional Aperture Directional Aperture for • Centred 150 from the Moon • FWHM ~7-300 in , 300 in • Significant lunar ‘shadow’ Peak Sensitivity to a Point Source Define Directionality: Peak sensitivity (km2) Effective aperture (km2 sr) Total solid angle (sr) • For Parkes Limb-Pointing, d=28 • Sensitivity will be highly directional • Observation Times Matter! The Lunar Cherenkov Technique: From Parkes Onwards

7. Parkes Directional Sensitivity Sensitivity to 10 ZeV neutrinos of the Parkes experiment Directional sensitivity in celestial coordinates: The Lunar Cherenkov Technique: From Parkes Onwards

8. 0 5.8 11.5 17.4 23.2 29 Approximate combined sensitivity to 10 ZeV neutrinos of the Parkes and GLUE experiments (Dates from Kalyazin unavailable) GLUE GLUE Sensitivity • Goldstone Lunar UHE Neutrino Experiment • 120 hr over 3 yrs • Approx. times from Williams (2004) APPROXIMATE! The Lunar Cherenkov Technique: From Parkes Onwards

9. Approximate combined sensitivity to 10 ZeV neutrinos of the Parkes, GLUE, and ANITA-Lite ANITA-lite (note log scale) ANITA-Lite Sensitivity • Concentrated in (Barwick et al 2004) • Uniform coverage assumed in this region Missing: • ANITA • Kalyazin • Auger • Hi-Res • … APPROXIMATE! Other et al. 2004 The Lunar Cherenkov Technique: From Parkes Onwards

10. Part 1 Summary: From Parkes Parkes Limit • Aperture comparable to other lunar Cherenkov experiments • Isotropic limits now obsolete • Potentially strong point-source limit Directional Sensitivity • Apertures are highly directional • Current limits are anisotropic • Scope for targeted observations of suspected sources • Complimentary experimental sensitivities The Lunar Cherenkov Technique: From Parkes Onwards

11. Part 2: Onwards • Currently: • UHE neutrinos have not be discovered • Lunar Cherenkov pulses unobserved • Current aim: remedy this! • Ultimate Aim: Perform UHE particle astronomy • Energy Resolution • Arrival Direction • Particle Type (CR or Neutrino) • How can this be achieved? The Lunar Cherenkov Technique: From Parkes Onwards

12. Moon Unresolved Sensitivity annular Moon ‘shadow’ < 50 Very broad sensitivity! Resolution of Arrival Direction Worst Case Reconstruction • Assumes no signal spectral information • Use inverse likelihood of detection • This is the directional sensitivity Moon Resolved Restricts signal origin Sensitivity narrows CONCLUDE: Use information on signal origin to reconstruct arrival direction. The Lunar Cherenkov Technique: From Parkes Onwards

13. Apparent Signal Origin • Apparent Signal Origin • The apparent signal exit position from lunar surface • Will be resolved using radio-arrays • Can be used to constrain the arrival direction • Simulated using a -fn antenna beam • Results: • Good resolution in (~100) • Poor res in (~700 !) • Offset depends on pointing position: Offset angle Apparent signal exit radius Lunar radius Apparent Signal Origin Inverse Likelihood We require a further parameter to constrain The Lunar Cherenkov Technique: From Parkes Onwards

14. Using Signal Polarisation Detecting Polarisation • Cherenkov signals are linear polarised • Polarisation aligns with shower track • Some distortion by refraction & roughness • Will restrict arrival direction, esp. in The Lunar Cherenkov Technique: From Parkes Onwards

15. Signal Polarisation: Simulation Results Results for and -Beam • Combined resolution ~100x100 • Weak energy dependence • Similar for cosmic rays At lower frequencies: • Roughness decreases (better resolution) • Cherenkov cone is wider (worse resolution) • Combined effect: worse resolution. • The effective aperture to high energy particles is greater. How can we get around this? The Lunar Cherenkov Technique: From Parkes Onwards

16. Spectral Information: Angle from Cherenkov cone Angular Dependence • The Cherenkov cone has finite width, • Hence uncertainty in the arrival direction. • is larger at low frequencies: • How to eliminate this uncertainty? Using Spectral Information • We need to measure , the angle to the shower axis • This can be derived from the observed signal spectrum • Dependence: The Lunar Cherenkov Technique: From Parkes Onwards

17. Determining Particle Type Cosmic Rays vs Neutrinos • Both should produce detectable pulses • Both interact with similar geometries • How can they be distinguished? Spectral Information • Cosmic rays interact at the surface • Neutrinos penetrate deep into the regolith • Regolith absorbs radio-waves Signal strength (V/m/MHz) Frequency (GHz) Shower depth (absorption lengths at 1 GHz) The Lunar Cherenkov Technique: From Parkes Onwards

18. The Square Kilometre Array ‘The International Radio Telescope for the 21st Century’ Minimal Specifications: • 1 km2 collecting area at 1.4 GHz • Frequency range 100 MHz to 25 GHz • Wide Bandwidths (up to 4 GHz) • Resolving power < 0.1 arcsec at 1.4 GHz • Proposed locations: South Africa or Australia Timeline • 2009 Final technology decision • 2010 Construction of prototypes begin • 2014 Construction of full array begins • 2020 First observations with full SKA The Lunar Cherenkov Technique: From Parkes Onwards

19. Summary Part 2 UHE Particle Astronomy with the Lunar Cherenkov Technique • Arrival direction can be reconstructed on an individual event basis using • Apparent signal origin (can be done for marginal events; requires long baselines) • Polarisation (accuracy depends on signal/noise) • Measurement of the spectrum (requires broad bandwidths) • Cosmic rays and neutrinos can be distinguished with a broad-bandwidth instrument • Neutrino energies will be hard/impossible to determine for most events (unknown inelasticity). • Simultaneous observations over a wide frequency range are critical. The Square Kilometre Array • Potentially an extremely powerful instrument for UHE particle astronomy • Technology/design decisions being made now • We require the radio-astronomy community to be convinced by this technique (pre-2009 observation would help!). We’re not that kind of lunatic! The Lunar Cherenkov Technique: From Parkes Onwards