1. 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.

2. 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

3. 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!

4. 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

5. 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 eV range
*(times from Williams 04)

6. 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.

7. 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

8. 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.

9. 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

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

11. 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?