0 April 22, 2013 A. Romero-Wolf Interferometry in UHE particle astrophysics Andres Romero-Wolf Jet Propulsion Laboratory, California Institute of Technology April 22, 2012 Interferometric Techniques for Impulsive Signals at Radio/Microwave Frequencies

1 April 22, 2013 A. Romero-Wolf Interferometry in UHE particle astrophysics Andres Romero-Wolf Jet Propulsion Laboratory, California Institute of Technology April 22, 2012 Interferometric Techniques for Impulsive Signals at Radio/Microwave Frequencies

2 April 22, 2013 A. Romero-Wolf Motivation First detection of ultra-high energy neutrinos are expected to lie close to the detector threshold. Increased demands for higher sensitivity techniques to reduce the detection threshold. Interferometric techniques have been applied for decades to detect weak signals.

3 April 22, 2013 A. Romero-Wolf Radio Interferometry Applied to Imaging and Astrometry

4 April 22, 2013 A. Romero-Wolf Imaging Image credit: M87 VLA VLBA Image Credit:

5 April 22, 2013 A. Romero-Wolf Astrometry Very Long Baseline Interferometry applied to identifying a source location. 200 µas (1 nanoradian) resolution. Applied to spacecraft navigation catalogues, measuring Earth motion parameters, plate tectonics, etc. Image Credit: O. Sovers, J. Fanselow, and C.S. Jacobs, Reviews of Modern Physics, Vol. 70, No. 4, October 1998 Delay and delay rate are partial derivatives of the phase.

6 April 22, 2013 A. Romero-Wolf Astrometry Astrometric Density Astrometric time-series display typical source location variations of 200 µas for the most compact sources. Image Credit: Image Credit: C.M. King, JPL / UH Manoa

7 April 22, 2013 A. Romero-Wolf Ultra-high Energy Particle Astrophysics

8 April 22, 2013 A. Romero-Wolf Ultra-high Energy Cosmic Rays 1 per 1000 km 2 per year 1 per 10 km 2 per year Charged particles of cosmic origin constantly bombard the Earth’s atmosphere. Protons and nucleons are observed with the energy of a well thrown fastball.

9 April 22, 2013 A. Romero-Wolf What are the sources of the highest energy particles observed in the Universe? Particles with energies > eV require very powerful and efficient accelerators. Active Galactic Nucleus Gamma Ray Bursts Supernova Remnants Inter-galactic magnetic shocks Magnetic Field Amplitude, Gauss Size, cm What Are The Sources of the Highest Energy Particles in the Universe?

10 April 22, 2013 A. Romero-Wolf Extended Air Showers Ultra-high energy cosmic rays interact with the Earth’s atmosphere to produce showers of secondary particles. These extended air showers are observed with particle counters on the ground and by UV fluorescence.

11 April 22, 2013 A. Romero-Wolf Geosynchrotron Radiation q=-|e| B q=+|e| Transverse current gives polarization vector. x z y v  v e- v e+ Magnetic field Shower Axis The extended air shower contains a significant quantity of positrons and electrons moving at nearly the speed of light. The Earth’s geomagnetic field separates the charges producing coherent synchrotron radiation

12 April 22, 2013 A. Romero-Wolf Radio Detection of Extended Air Showers Radio image produced by cosmic ray impulse data from the LOPES detector. First observed in the 1960’s by Jelley. Active field during the 1960’s and 1970’s. The technique has been revived in the last decade with modern radio detection techniques.

13 April 22, 2013 A. Romero-Wolf Cosmic Rays and Neutrinos Cosmic photon backgrounds attenuate UHECR energy Interaction threshold at 4x10 19 eV UHECRs observed with E>4x10 19 eV must be within 100 MPc Cosmic Distance Scales Milkyway: 30 kpc Andromeda: 800 kpc away. Cen A: 4Mpc Virgo Cluster: 17 Mpc Coma Cluster: 90 Mpc

14 April 22, 2013 A. Romero-Wolf Neutrino Radio Detection Cosmic Neutrino Target Dense and RF Transparent Interaction point Particle shower 20% charge excess Radio Emission Coherent Cherenkov Radiation Cone Antenna Detector in Target Antenna Detector Outside of Target L< RICE Dipole antennas in South Pole ice. SALSA Antennas in salt domes ARA Large detector antenna network in South Pole GLUE Lunar regolith target with DSN antenna.

15 April 22, 2013 A. Romero-Wolf The ANITA Ultra-high Energy Particle Telescope 15 Synoptic horn antenna array ( MHz) Circumpolar trajectory on a balloon.

16 April 22, 2013 A. Romero-Wolf Neutrino Limits with ANITA ANITA provides the strongest limits to ultra-high energy neutrino fluxes to date. Several models of ultra-high energy neutrino production have been ruled out.

17 April 22, 2013 A. Romero-Wolf Geosynchrotron Radiation Detected with ANITA. Detected with ANITA in UHF band ( MHz). ANITA-3 (2013) will be tuned to detect hundreds. Radar backscatter amplitude

18 April 22, 2013 A. Romero-Wolf Interferometry in Ultra-high Energy Particle Astrophysics

19 April 22, 2013 A. Romero-Wolf Impulse Response Time Frequency Time Frequency Electric Field Electric Field Voltage Impulse response Or Effective Height v = E ★ h ANITA horn antenna effective height

20 April 22, 2013 A. Romero-Wolf Geometric Delay Beam forming combines the signals from multiple antennas. The geometric delay is the basic quantity that connects multiple observations of the same signal.

21 April 22, 2013 A. Romero-Wolf The ANITA Array ANITA antenna array observes the same impulse with multiple channels. The array is unusual in that the antennas are not all pointed in the same direction. The arrangement is designed for full azimuthal coverage.

22 April 22, 2013 A. Romero-Wolf Beam-forming The signals from the previous slide are aligned in time according to the true geometric delay of the signal. The directional response of the antennas does not affect the phase of the signal and it can be added coherently.

23 April 22, 2013 A. Romero-Wolf Coherently Summed Waveform Power Global image of the coherently summed power for each assumed direction of the incident radiation. The direction of true incidence presents itself as a sharp peak. The diametrically opposed direction sees the thermal noise background.

24 April 22, 2013 A. Romero-Wolf Beam-forming with Cross-correlations Cross-correlations of an impulsive signal event. The time-domain cross-correlation is mapped to incident direction via the geometric delay relation.

25 April 22, 2013 A. Romero-Wolf Beam-forming with Cross-correlations Example of a global coherence map derived from the sum of cross-correlations. The true direction of the signal presents itself as a sharp peak. The map is analogous to the dirty map of radio interferometry.

26 April 22, 2013 A. Romero-Wolf Beam-forming with Cross-correlations Examples of signals and background s detected with ANITA.

27 April 22, 2013 A. Romero-Wolf Angular Error The ANITA array has < 1-degree angular errors. This is due to the ultra-wideband signals used in the correlation. ANITA-I

28 April 22, 2013 A. Romero-Wolf Angular Error The ANITA array has < 1-degree angular errors. This is due to the ultra-wideband signals used in the correlation. ANITA-II

29 April 22, 2013 A. Romero-Wolf Summed Waveforms vs. Cross-Correlations The relation between the summed waveform signal to noise ratio and cross- correlation coefficient reveals features that are specific to each kind of signal and background.

30 April 22, 2013 A. Romero-Wolf Thermal Noise Rejection A discriminant formed by the linear combination of the cross correlation coefficient and the peak of the summed waveform provides a highly efficient filter.

31 April 22, 2013 A. Romero-Wolf Discrimination Techniques Thermal noise and carrier wave signal backgrounds both have comparable peak and secondary lobes.

32 April 22, 2013 A. Romero-Wolf Signal Strength The peak of the coherent waveform sum provides additional efficient discrimination between signals of interest and thermal noise.

33 April 22, 2013 A. Romero-Wolf Imaging the Sun Averaging events in a sun-centered coordinate system reveals a radio image of the sun along with its reflection on the ice. These images can be used to measure the surface roughness of the ice. See talk by J. Stockham.

34 April 22, 2013 A. Romero-Wolf Imaging Anthropogenic Backgrounds Clusters of events that pass all cuts provide locations of anthropogenic backgrounds. Not all clusters originate from identified field camps.

35 April 22, 2013 A. Romero-Wolf Imaging Anthropogenic Backgrounds Average Correlation Coefficient ANITA-1 Imaging of all data, including thermal noise, provides a complementary view of the Antarctic noise sources.

36 April 22, 2013 A. Romero-Wolf Imaging Anthropogenic Backgrounds Average Correlation Coefficient ANITA-2

37 April 22, 2013 A. Romero-Wolf Conclusions Pulse-phase interferometry offers highly sensitive techniques for analysis of ultra-high energy particle transients. Implementation of this technique into a real-time digitization and triggering scheme can yield improvements in detection sensitivity. Research described herein done under contract with NASA. Copyright ©2013 Jet Propulsion Laboratory, California Institute of Technology. Government sponsorship acknowledged.