LUNASKA

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

Radio Telescopes Radio Telescopes

Clancy W. James, University of Adelaide

(Supervisors: R. Protheroe, R. Ekers)

LUNASKA

?

GZK Neutrinos• UHE protons interact with

CMBR (GZK Interactions)

• Neutrino secondaries

What are these cosmic accelerators?

Is there a cut-off to the spectrum?

The ‘Ideal Messengers’The ‘Ideal Messengers’

Neutrinos:• Travel in strait lines – source

identification!• Rarely interact – observed

flux = source flux!

neutrino

protongamma

*

?

B-Fields

LUNASKA

Auger: CR-AGN Correlation Auger: CR-AGN Correlation Science 318 (2007)Science 318 (2007)

• CR can be used for astronomy• More statistics needed

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The Askaryan EffectThe Askaryan Effect

eV 1018

eV 102 17

10

,,10~

een

910~ eenn

2. Cascade of secondaries3. Negative charge

excess

22 qE

22 qE

4. Coherent Cherenkov radiation

O(3m)

O(1

0cm

)5. Dense medium: Coherency

in GHz regime.

1. UHE particle interaction

13 Sep 2004R. Ekers

6

LUNASKA

The Lunar Cherenkov TechniqueThe Lunar Cherenkov Technique

neutrino

radio waves(coherent Cherenkov radiation)

shower

cosmic ray

GRB? DM?AGN?

“A radio method to determine the origin of the highest-energy neutrinos and cosmic rays."

SKA

WSRTGoldstone ATCAParkes Kalyazin

LUNASKA

Signature• Nanosecond-duration pulses

• These are transients!

• Must be distinguished against a thermal and RFI background

• This requires non-standard methods!

Coherent Cherenkov RadiationCoherent Cherenkov Radiation

Spectrum• Broadband (peak < 5 GHz)

• 100% linearly polarised

• Coherent emission process

• Scaling in the coherent regime:– Voltage V:– Received power: 2

)(E

Spectrum PredictedObservation

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Experimental HistoryExperimental History

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)

NO UHE Neutrinos Observed.

How can we improve?

LUNASKA

SKA – the Square Kilometre ArraySKA – 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?

LUNASKA

LUNASKALUNASKA

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 Lunar UHE Neutrino Astrophysics with the Astrophysics with the

Square Kilometre Array”Square Kilometre Array”

LUNASKA

Experimental HurdlesExperimental Hurdles

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!

LUNASKA

Ionospheric DispersionIonospheric Dispersion

Low frequencies

High frequencies

Night, solar cycle min

Day, solar cycle max

• Ionospheric dispersion destroys the characteristic coherency of the pulses

• The effect is worse during the day, at low frequencies, and at solar cycle max

LUNASKA

DedispersionDedispersion

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

LUNASKA

DedispersionDedispersion

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?

Terrestrial Impulse? True Event? Satelite-bounce?

Predictions – from a 3am Analysis

Observed Trigger

LUNASKA

Timing Callibration: 3C273Timing Callibration: 3C273

• Point antennas at a point source (bright quasar)• Trigger off the noise cal pulse• Correlate resulting buffers between antennas.

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2007 Observations2007 Observations

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

Instantaneous Aperture

NO PULSES DETECTED

LUNASKA

Theoretical HurdlesTheoretical Hurdles

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.

LUNASKA

Limb BrighteningLimb Brightening

• Various geometrical effects mean we expect more signals from the lunar limb (limb brightening).

• The effect is greatest at:– Low energies

– High frequencies

Small dishes(large beams)

PAFs orMultibeams

LUNASKA

Instantaneous SensitivityInstantaneous 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!

LUNASKA

Current UHE LimitsCurrent UHE Limits

• 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)

10^22 eV

Target Here

LUNASKA

PolarisationSignal Exit PositionInstantaneous Aperture

Reconstructing Arrival DirectionReconstructing Arrival Direction

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.

5

This is a simplistic procedure

LUNASKA

SKA Sensitivity to UHE NeutrinosSKA Sensitivity to UHE Neutrinos

• UHE neutrino cross-section• Small scale surface roughness

Uncertainties:• Depth of the regolith

LUNASKA

SKA Sensitivity to UHE CRSKA Sensitivity to UHE CR

Uncertainties:• Large-scale surface roughness• ‘formation zone’ effects

LUNASKA

SummarySummary

• 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!