LUNASKA The Directional Dependence of the Lunar Cherenkov Technique in Regards to UHE Neutrino Detection -C.W. James (University of Adelaide) IF we want to test for anisotropies in the UHE neutrino flux, THEN the directional dependence of our instruments matters, ELSE those only interested in the spectra can sleep for 15 minutes.

Directional Dependence of LCT Definitions: (km2 sr) Effective aperture. (km2) Effective area. Directionally dependent effects: UHE cannot penetrate the Moon – ‘skimming’ geometry. Narrow Cherenkov cone (esp at high frequencies). Refraction at the surface, roughness etc. Beam selection effect

Instantaneous Sensitivity of Parkes Treat the Moon-Telescope System as an instrument. What is its ‘beam pattern’? Peak sensitivity to a point source is many times the solid-angle averaged value. Conclusion: we can make targeted observations!

Targeting Suspected Sources We can choose observation time and beam pointing position to maximise exposure to suspected sources of UHE nu. If the maximum cross-section is We defined the ‘directionality’ as the ratio: is highest for: Large dish sizes (small beams) High frequencies (narrow radiation pattern, small beams) Low energies (small range of geometries detectable). Limb-pointing. Where are current limits strongest? Write Integrate Parkes (GLUE, Kalyazin similar) 1021 eV 1022 eV 1023 eV Limb 28 20 15 Centre 10 8

Pre-ATCA LCT Limits at 1022 eV Target here! Contours are GLUE* + Parkes only (Kalyazin times unavailable) ANITA / ANITA-lite dominates, but confined to (yellow) FORTE kicks in at around 1023 eV. Qualitatively similar over the 1021 - 1023 eV range *(times from Williams 04)

Instantaneous Aperture of ATCA Limb-Pointing Centre-Pointing APPROXIMATE! km2 Here the isotropic aperture is less in limb-pointing mode, but the peak sensitivity is greater.

ATCA Cen A / Sg A Targeting APPROXIMATE! Exposure to UHE nu (km2 days) 1021 eV 1022 eV 1023 eV Sg A 0.5 14 175 4.2 90 740 Cen A 0.015 2.1 43 9.3 147 1010 Parkes & GLUE Parkes, GLUE & ATCA

Coverage for long-term observations Instantaneous aperture becomes less relevant as: Beam size increases, making pointing position irrelevant. Next gen instruments using small dishes. More focus on lower frequencies. Observations spread over an entire (or many) lunar cycles, eliminating choice of observation time. Long runs with current instruments (P. Kalberla) Next generation radio instruments (LOFAR, SKA) using aperture arrays reduce competition for time. But we are still confined to observing the Moon in its orbit! Integrate Potential sensitivity will depend on the angular offset to the lunar orbital plane.

Coverage of Future Experiments } SKA Lunar orbit: nodal precession period 18.6 years 5.50 inclination to ecliptic. Coverage of the SKA will not be uniform until 1021 eV. Gaps near ecliptic poles not covered by ANITA Other experiments not relevant above 1018 eV

Cosmic Rays UHE CR exist and are anisotropic at E>1019.6 eV Simulation more problematic surface roughness formation-zone effects (AUGER)

Summary UHE neutrinos are touted as allowing source identification. Current limits at ~ZeV energies are anisotropic for all experiments (future limits likely will be also) Observation dates / beam pointing positions can be chosen to optimise sensitivity to suspected UHE neutrino sources / areas of the sky with weak limits. More work needed for CR – we expect results to be qualitatively similar. QUESTION: From what directions do we expect UHE neutrinos to come?