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1April 22, 2013 A. Romero-Wolf
Interferometry in UHE particle astrophysics
Andres Romero-WolfJet Propulsion Laboratory,
California Institute of Technology
April 22, 2012
Interferometric Techniques for Impulsive Signals at Radio/Microwave Frequencies
2April 22, 2013 A. Romero-Wolf
Interferometry in UHE particle astrophysics
Andres Romero-WolfJet Propulsion Laboratory,
California Institute of Technology
April 22, 2012
Interferometric Techniques for Impulsive Signals at Radio/Microwave Frequencies
3April 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.
4April 22, 2013 A. Romero-Wolf
Radio Interferometry Applied to Imaging and Astrometry
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Imaging
Image credit: http://www.nrao.edu/images/M87_trifold.jpg
M87
VLA
VLBA
Image Credit: http://www.vlba.nrao.edu/sites/
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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.
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Astrometry
Astrometric Density
Astrometric time-series display typical source location variations of 200 µas for the most compact sources.
Image Credit: http://astrogeo.org/images/J2236+2828/J2236+2828_X_2003_05_07_pus_map.ps
Image Credit: C.M. King, JPL / UH Manoa
Image Credit: C.M. King, JPL / UH Manoa
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Ultra-high Energy Particle Astrophysics
9April 22, 2013 A. Romero-Wolf
Ultra-high Energy Cosmic Rays
1 per 1000 km2 per year
1 per 10 km2 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.
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What are the sources of the highest energy particles observed in the Universe?
Particles with energies > 1020 eV require very powerful and efficient accelerators.
Active Galactic Nucleus
Gamma Ray Bursts
Supernova Remnants
Inter-galactic magnetic shocks
Mag
netic
Fie
ld A
mpl
itude
, Gau
ss
Size, cm
What Are The Sources of the Highest Energy Particles in the Universe?
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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.
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Geosynchrotron Radiation
q=-|e|
B
q=+|e|
Transverse current gives polarization vector.
xz
y
v
ve- ve+
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
13April 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.
14April 22, 2013 A. Romero-Wolf
Cosmic Rays and Neutrinos
• Cosmic photon backgrounds attenuate UHECR energy
• Interaction threshold at 4x1019 eV
• UHECRs observed with E>4x1019 eV must be within 100 MPc
Cosmic Distance ScalesMilkyway: 30 kpcAndromeda: 800 kpc away.Cen A: 4MpcVirgo Cluster: 17 MpcComa Cluster: 90 Mpc
15April 22, 2013 A. Romero-Wolf
Neutrino Radio Detection
CosmicNeutrino
TargetDense and RF Transparent
Interactionpoint
Particle shower20% charge excess
Radio EmissionCoherent Cherenkov Radiation Cone
Antenna Detector in Target
Antenna Detector Outside of Target
L<
RICE Dipole antennas in South Pole ice.
SALSAAntennas in salt domes
ARALarge detector antenna network in South Pole
GLUELunar regolith target with DSN antenna.
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The ANITA Ultra-high Energy Particle Telescope
16
• Synoptic horn antenna array (200-1200 MHz)
• Circumpolar trajectory on a balloon.
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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.
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Geosynchrotron Radiation Detected with ANITA.
• Detected with ANITA in UHF band (200-1200 MHz).• ANITA-3 (2013) will be tuned to detect hundreds.
Radar backscatter amplitude
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Interferometry in Ultra-high Energy Particle Astrophysics
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Impulse Response
Time
Frequency
Time
Frequency
Ele
ctric
F
ield
Ele
ctric
F
ield
Vo
ltag
eV
olta
ge
Impulse response Or Effective Height
v = E ★ h
ANITA horn antenna effective height
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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.
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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.
23April 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.
24April 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.
25April 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.
26April 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.
27April 22, 2013 A. Romero-Wolf
Beam-forming with Cross-correlations
Examples of signals and backgrounds detected with ANITA.
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Angular Error
The ANITA array has < 1-degree angular errors.
This is due to the ultra-wideband signals used in the correlation.
ANITA-I
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Angular Error
The ANITA array has < 1-degree angular errors.
This is due to the ultra-wideband signals used in the correlation.
ANITA-II
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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.
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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.
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Discrimination Techniques
Thermal noise and carrier wave signal backgrounds both have comparable peak and secondary lobes.
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Signal Strength
The peak of the coherent waveform sum provides additional efficient discrimination between signals of interest and thermal noise.
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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.
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Imaging Anthropogenic Backgrounds
Clusters of events that pass all cuts provide locations of anthropogenic backgrounds.
Not all clusters originate from identified field camps.
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Imaging Anthropogenic Backgrounds
Average Correlation Coefficient
ANITA-1
Imaging of all data, including thermal noise, provides a complementary view of the Antarctic noise sources.
37April 22, 2013 A. Romero-Wolf
Imaging Anthropogenic Backgrounds
Average Correlation Coefficient
ANITA-2
38April 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.
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