Lunar Radio Cerenkov Observations of UHE Neutrinos Ron Ekers CSIRO ARENA 2008 Rome, 25-27 June 2008 Invited talk at XXIII Texas Symposium on Relativistic Astrophysics 2006 23 June 2008

Lunar Cherenkov emission neutrino photon shower

Summary History of lunar Cerenkov experiments Basic technology Low or High frequency Telescope arrays Future developments and UHE neutrino sensitivity 23 June 2008

First radio experiment Parkes 64m radio telescope Jan 1995 Triggered by Adelaide ICRC meeting Receiver: 1.2 – 1.9 GHz. (SETI receiver) Used existing pulsar equipment Bandwidth: 475 MHz 2 sec time resolution. Beamwidth: 13 arc min. Moon ~ 30 arc min, hence reduced sensitivity at Moon’s limb ! Hankins, Ekers & O’Sullivan MNRAS 283, 1996

Basic requirements Radio receivers (0.1-3GHz) Sensitivity 10-300cm Sensitivity aperture >> 20m diameter Observing time >> weeks GHz bandwidth and η sec time resolution Radio Frequency Interference (RFI) discrimination Good site Real time pulse detection logic and data recorder Post trigger data processing 23 June 2008

Terrestrial Interference Forte satellite: 131MHz FORTÉ satellite: 131 MHz 10 Dec 2006

Pulse dispersion effects  t =  .  ne dl . -3 ionosphere t = 20 sec interstellar medium t = 10 sec E M Galactic radio pulse t = 10 sec Moon bounce t = 2x 20 sec Lunar Cherenkov t = 20 sec Terrestrial interference t = 0 -( 10 Dec 2006

Ionospheric Dispersion Estimation TEC (total electron content) is derived from dual frequency GPS Provided on line by NASA crustal dynamics program Not available in real time Some model error for a given line of site Use simultaneous measurement of the Faraday Rotation of polarised lunar limb emission Model field distribution => TEC in realtime 23 June 2008

Goldstone Lunar Neutrino Search 1998 GLUE NASA 70m DSN antenna Peter Gorham, David Saltzberg, Dawn Williams First observations late 1998: approach based on Hankins et al. 1996 results from Parkes 1999: add 2nd 34 m antenna DSS13 Dual trigger from both antenna Removes local interference updated 10 Dec 2006

Neutrino Flux Limits Goldstone ~30 hrs Goldstone No events above net 5 sigma Gorham, Saltzberg et al RADHEP-2000, 177 (2001). New Monte Carlo estimates: Full refraction raytrace, including surface roughness, absorption Parkes Sensitivity 2.5x Goldstone But only 1hr on limb 2003: 120 hours on source Gorham et al, Phys Rev Lett 93, 41101 (2004) Updated version needs more updates with new (GLUE) sensitiovity limits which have changed and which are still wrong ~30 hrs Goldstone No events above net 5 sigma 10 Dec 2006

Historical Limits on total UHE neutrino flux James and Protheroe arXiv:0802.3562v2 23 June 2008

Detecting the pulse Minimum neutrino energy Determined by pulse detection threshold, hence radio telescope sensitivity GHz frequencies better Moves curve to left Neutrino flux limit determined by Volume of neutrino detector Acceptance solid angle Lower frequency better Observing time Moves curve down 10 Dec 2006

pulse detection threshold Signal antenna gain proportional to antenna area but.... bandwidth Noise thermal emission from moon Moon unresolved (7m-22m) – increases with antenna size Moon resolved (>20m) - independent of dish size Correlated between elements sky noise becomes dominant at about 100MHz (moon then colder than sky)! receiver noise not very important for this experiment Ionospheric dispersion can be fully corrected and can help if few bit sampling used will increase detection threshold if too uncertain 23 June 2008

Sensitivity v Antenna Diameter Modify title 10 Dec 2006

Balancing trigger and post processing sensitivity At GHz bandwidth raw data rates exceed current computer capacity x10 now but decreasing A trigger and data dump strategy is necessary The experimental sensitivity is almost entirely determined by the trigger level Requires real-time coherent ionospheric dispersion Requires sophisticated high speed real-time logic 23 June 2008

Some Hardware Issues Wideband transistor receivers Usually cryogenically cooled in radio telescopes Dual orthogonal polarizations (linear or circualar) Wide bandwidth system Avoid reflections (unwanted modes) Fast detection logic State of art FPGA’s Careful circuit design 23 June 2008

Sensitivity v Antenna Diameter multiplex Modify title 10 Dec 2006

Seeing all the moon Event rates highest at the limb 30’ Event rates highest at the limb Noise contribution from all moon We want to observe the entire lunar limb 20m dish 64m dish array 23 June 2008

Imaging antenna

Beamforming Array  t Phased array ( Vi )2 I() ( Vi )2 I x2 Split signal no S/N loss t Phased array ( Vi )2 I() ( Vi )2 I

Coherent Beamforming Arrays Noise dominated by thermal emission from moon Increasing antenna size doesn’t help Aperture plane or Focal plane Arrays of small antenna (eg ATCA-SKA) Form multiple beams from multiple antennas Coherent addition of signals Enough beams to cover all moon Multiple beams in a large dish Eg Parkes + focal plane array Max signal from limb of moon Needs fully sample focal plane array Beam former to illuminate whole limb New version – with corrected beamforming 23 June 2008

Radio Experiments some issues to consider Broadband continuum pulse 1-3GHz , Δt = 0.5 ηsec Ionospheric dispersion 10-50 ηsec at 2 GHz, 10-50 μsec at 0.2 GHz Coherent de-dispersion necessary Avoid solar maximum? Linearly polarised signal Measure both orthogonal polarizations φ gives position around cone, hence position on sky Pulse detection on each beam at 0.5nS resolution Real time dump and store events Coincidence detection for Interference rejection Pulse coincidence detection for spaced antennas Anti-coincidence using multiple beams in one antenna modified 23 June 2008

Position determination Interferometer measures position of pulse Source lies on the Cherenkov cone (56o) Linear polarization with radial distribution * Includes intensity variation around the cone which removes the amiguity Measure polarization Two possible positions One less probable 10 Dec 2006

Radio Lunar Cerenkov Experiments Parkes 64m 1.5 GHz 1995 Goldstone 70+32m 2.2 GHz 1998- Kalyazin 64m 1.4-8 GHz 2005 WSRT 14x25m 0.15 GHz 2006 observing ATCA 6x22m 1.5 GHz 2007 observing LOFAR phased array 0.1 GHz Future ASKAP 30x12m 1.0 GHz Future SKA 1500x20m 1.0 GHz Proposed ELVIS lunar orbiter Proposed LORD lunar orbiter Proposed

Effective Aperture James and Protheroe , 2008 23 June 2008

Low Frequency Experiments <500MHz Scholten et al astoph/0508580 Weaker pulses but large acceptance angle Higher energy cutoff - 1022 eV Flux limit lower (x10-100) Many issues Modest bandwidth so easier signal processing Cheaper collecting area Strong assumption about depth of regolith (500 v 10m) UHE Cosmic ray “contamination” No positional information Huge ionospheric dispersion correction needed Radio frequency interference

Square Kilometre Array 2015-2020 23 June 2008

SKA Aperture Array 70-500MHz 23 June 2008

SKA Poster 10 Dec 2006

SKA configuration Trigger off core Keep long baselines in a buffer Inner core Station Keep long baselines in a buffer Combine high and low frequency triggers

UHE neutrino models and future experimental limits James and Protheroe arXiv:0802.3562v2 23 June 2008

China FAST Karst region for array of large Arecibo-like Telescopes Diameter 600 m Add a video clip

Phased Array Feeds Full aperture Whole moon 23 June 2008

Installing the Parkes 21cm Multibeam Receiver 10 Dec 2006

Conclusions Fruitful interaction between radio astronomy and high energy particle communities Some culture differences Big improvements in signal processing technology Significant sensitivity improvements since 1995 Sensitivity estimates have been improved Sensitivity estimates don’t all agree (many assumptions) High v low frequency? Future sensitivity improvements will need antenna arrays or focal plane arrays Proposed future radio facilities will probe all UHE models Strategy for targeted experiments is different 23 June 2008