“Lunar UHE Neutrino Astrophysics with the Square Kilometre Array” LUNASKA Status Report and Future Prospects on LUNASKA Lunar Observations with ATCA R. Ekers (CSIRO ATNF) C. James (U. Adelaide) R. McFadden (U. Melbourne) C. Phillips (CSIRO ATNF) R. Protheroe (U. Adelaide) P. Roberts (CSIRO ATNF) “Lunar UHE Neutrino Astrophysics with the Square Kilometre Array”

The Australia Telescope Compact Array ATCA 6x22m dishes in NSW, Australia Aperture synthesis antenna 6km E-W Baseline We are using this to develop methods and technology scaleable to the SKA Why ATCA? Beamwidth at 1-2 GHz matched to lunar disk. Array RFI rejection Techniques scalable to SKA CABB upgrade FPGA-based back-end Current 600 MHz Bandwidth It’s close! Development Dedispersion Triggering (fast logic) RFI discrimination Observations!

Experimental Set-Up 1 Gbit Ethernet Link (TCP/IP) Offline Processing Data Channels: 3 antennas. Dual linear polarisation. 600 MHz Bandwidth (1.2-1.8 GHz). 8-bit, 2 GHz sampling Triggering: Independent at each antenna. Adjustable threshold trigger on each polarisation. If either polarisation exceeds the threshold, 128ns buffers from both are recorded. 256 MHz clock time also recorded. Saturation rate 1 kHz / antenna. 1 Gbit Ethernet Link (TCP/IP) Baseband Buffer Offline Processing

System Detail at Each Antenna LNA 1.5 Ghz 2.3 Ghz 1.5 GHz Polarisation and Band Splitter L-Band RF Splitter Module (F10) S-Band Splitter (C23) L-Band Splitter (C22) S-Band RF Splitter Module (F11) 1.2 – 2.5 Ghz Horn Pol A Pol B Receiver (we use L-band: nominal 1.2-1.8 GHz) Standard ATCA Receiving Path Customised Hardware Analogue De-dispersion Filters 3 – 8 ns (night – day) 2.048 Gs/s 8 bit ADC Buffer Ethernet Connection Adjustable Threshold Detection 5.1 σ 4096 samples, 2μs ATNF BCC Interface 100Mb/s CABB Sampler Board ( McFadden et al)

Dedispersion Method Typical Night-time Dispersion We cannot digitally de-disperse or measure TEC in real time. VTEC at ATCA during May 2006: The ionosphere is stable between sunset and sunrise. Mean vertical dispersion ~4ns over 1.2-1.8 Ghz for 10pm-6am Hardware De-dispersion Filter Designed by Paul Roberts Correct for dispersion using an analogue microwave filter with a continuously-changing profile. Filters set for characteristic VTEC at 600 elevation. Thick Thin

Dispersion as RFI Discrimination Observed Trigger Results from May 2007 We can use the dispersion to discriminate against terrestrial RFI E.g. we were observing regular, strong triggers of ~20ns duration (opposite). Was the origin: A) Terrestrial (no dispersion) B) Lunar (characteristic dispersion) C) Satellite bounce (double dispersion)? A) Terrestrial Impulse? B) True Event? C) Satelite-bounce? Predictions – from a 3am Analysis

Correlation Str (arb units) Timing Calibration: 3C273 Correlation Str (arb units) NOTE: x-scale should read ns

ATCA Run Summary May 5th-7th 2007 (5 hr) 2007 Data Reduction 10pm-6am. Simultaneous baseband recording (64 Mhz at 1.2 GHz). Targeted Sag A region. Centre-pointing. Only ms timing available! Feb 26th-28th 2008 (14 hr) Repeat of ’07 set-up. 14 hrs stable configuration. March 17th-19th 2008 (20 hr) Targeted Cen A. Pointed at limb to maximise Cen A sensitivity. 2007 Data Reduction 120,000 candidates per antenna. 300 remain after 1 ms coincidence and ‘dumb’ RFI cuts. 4 remain after polarisation + ‘smart’ RFI cuts. We expect ~6 false events. ASSUME: No neutrinos. 2008 Analysis Pending… Relative nanosecond timing will give 4/1012 chance of a false detection. More RFI shielding on equipment, faster network => more sensitivity.

ATCA Sensitivity ATCA Sensitivity Simulations results: 600 MHz Bandwidth (1.2-1.8 GHz) Dual Polarisation 3 Antennas Threshold F.O.M.: Parkes: 3000 MHz m2 /K GLUE: 4500 Mhz m2/K ATCA: 5000 MHz m2/K Other Factors: Beam views entire lunar limb. lower. Independent triggering! Sensitivity of approx 2 beams only. Simulations results: Threshold comparable to Parkes, GLUE, Kalyazin etc. Relative improvement with energy. Calculated explicitly for 2007 only. Slight improvement in 2008. (my calculations) PRELIMINARY!

Expected ATCA Limit ATCA We have not finished analysing 2008 data. Plot approximate limit on an isotropic flux assuming no detections. Range reflects the regolith depth (upper: 10m, lower: ~ ) ATCA PRELIMINARY!

Other Notes Triggering Next Steps: Future: Independent triggering now limits our sensitivity. We await improved methods to go to >3 antenna. The ns radio environment is strange Most short-duration RFI unexplained. Can dominate individual trigger rates. This makes it hard to predict experimental sensitivity in advance! Offline vs Real Time processing Offline data reduction is easy. Real-time logic is hard. Sensitivity is limited by triggering logic. Next Steps: Real-time coincidence detection between antennas, RFI filtering. 1 week planned Feb/March 09 Future: Utilise full 1-3 GHz bandwidth 28+ day observations. Coherent beamforming? >3 antenna? Parkes Multibeam: 13 separate receivers. Any 3 match the lunar limb. Use 500 Mhz b/w. 12,000 MHz m2/K

In Conclusion… Primary goal – to learn lessons which can be extended to the SKA. Our effective aperture is higher than previous experiments, and has been improving – but soon we will come against limits of technology. Isotropic sensitivity currently well below ANITA. (but as for targeted observations – see my next talk!) Sensitivity to UHE CR unknown – more theoretical work needed here. LUNASKA is an ongoing project – we’ll keep you posted.