0 April 22, 2013 A. Romero-Wolf Interferometry in UHE particle astrophysics Andres Romero-Wolf Jet Propulsion Laboratory, California Institute of Technology

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


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


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.


Radio Interferometry Applied to Imaging and Astrometry


Imaging

Image credit: http://www.nrao.edu/images/M87_trifold.jpg

M87

VLA

VLBA

Image Credit: http://www.vlba.nrao.edu/sites/


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.


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


Ultra-high Energy Particle Astrophysics


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.


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?


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.


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


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.


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


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.


The ANITA Ultra-high Energy Particle Telescope

16

• Synoptic horn antenna array (200-1200 MHz)

• Circumpolar trajectory on a balloon.


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.


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


Interferometry in Ultra-high Energy Particle Astrophysics


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


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.


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.


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.


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.


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.



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.



Examples of signals and backgrounds detected with ANITA.


Angular Error

The ANITA array has < 1-degree angular errors.

This is due to the ultra-wideband signals used in the correlation.

ANITA-I


Angular Error

The ANITA array has < 1-degree angular errors.

This is due to the ultra-wideband signals used in the correlation.

ANITA-II


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.


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.


Discrimination Techniques

Thermal noise and carrier wave signal backgrounds both have comparable peak and secondary lobes.


Signal Strength

The peak of the coherent waveform sum provides additional efficient discrimination between signals of interest and thermal noise.


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.


Imaging Anthropogenic Backgrounds

Clusters of events that pass all cuts provide locations of anthropogenic backgrounds.

Not all clusters originate from identified field camps.



Average Correlation Coefficient

ANITA-1

Imaging of all data, including thermal noise, provides a complementary view of the Antarctic noise sources.



Average Correlation Coefficient

ANITA-2


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.

Documents

0 April 22, 2013 A. Romero-Wolf Interferometry in UHE particle astrophysics Andres Romero-Wolf Jet Propulsion Laboratory, California Institute of Technology