251 research outputs found
A Search for AGN sources of the IceCube Diffuse Neutrino Flux
The origin of the diffuse astrophysical neutrino flux measured by the IceCube
Observatory remains largely unknown. Although NGC 1068 and TXS 0506+056 have
been identified as potential neutrino sources, the diffuse flux of neutrinos
must have additional sources that have not yet been identified. Here we
investigate potential correlations between IceCube's neutrino events and the
Fermi and MOJAVE source catalogs, using the publicly-available IceCube data
set. We perform three separate spatially-dependent, energy-dependent, and
time-dependent searches, and find no statistically significant sources outside
of NGC 1068. We find that no more than 13% of IceCube's neutrino flux
originates from blazars over the whole sky. Then, using an energy-dependent
likelihood analysis, the limit on neutrinos originating from blazars reduces to
9% in the Northern hemisphere. Finally, we set limits on individual sources
from the MOJAVE radio catalog after finding no statistically significant
time-flaring sources.Comment: 18 pages, 7 figure
Development Toward a Ground-Based Interferometric Phased Array for Radio Detection of High Energy Neutrinos
The in-ice radio interferometric phased array technique for detection of high
energy neutrinos looks for Askaryan emission from neutrinos interacting in
large volumes of glacial ice, and is being developed as a way to achieve a low
energy threshold and a large effective volume at high energies. The technique
is based on coherently summing the impulsive Askaryan signal from multiple
antennas, which increases the signal-to-noise ratio for weak signals. We report
here on measurements and a simulation of thermal noise correlations between
nearby antennas, beamforming of impulsive signals, and a measurement of the
expected improvement in trigger efficiency through the phased array technique.
We also discuss the noise environment observed with an analog phased array at
Summit Station, Greenland, a possible site for an interferometric phased array
for radio detection of high energy neutrinos.Comment: 13 Pages, 14 Figure
Measurements and Modeling of Near-Surface Radio Propagation in Glacial Ice and Implications for Neutrino Experiments
We present measurements of radio transmission in the 100 MHz range
through a m deep region below the surface of the ice at Summit
Station, Greenland, called the firn. In the firn, the index of refraction
changes due to the transition from snow at the surface to glacial ice below,
affecting the propagation of radio signals in that region. We compare our
observations to a finite-difference time-domain (FDTD) electromagnetic wave
simulation, which supports the existence of three classes of propagation: a
bulk propagation ray-bending mode that leads to so-called "shadowed" regions
for certain geometries of transmission, a surface-wave mode induced by the
ice/air interface, and an arbitrary-depth horizontal propagation mode that
requires perturbations from a smooth density gradient. In the non-shadowed
region, our measurements are consistent with the bulk propagation ray-bending
mode both in timing and in amplitude. We also observe signals in the shadowed
region, in conflict with a bulk-propagation-only ray-bending model, but
consistent with FDTD simulations using a variety of firn models for Summit
Station. The amplitude and timing of our measurements in all geometries are
consistent with the predictions from FDTD simulations. In the shadowed region,
the amplitude of the observed signals is consistent with a best-fit coupling
fraction value of % (0.06% in power) or less to a surface or horizontal
propagation mode from the bulk propagation mode. The relative amplitude of
observable signals in the two regions is important for experiments that aim to
detect radio emission from astrophysical high-energy neutrinos interacting in
glacial ice, which rely on a radio propagation model to inform simulations and
perform event reconstruction.Comment: 14 pages, 13 figures, version accepted to PR
High-Precision Scanning Water Vapor Radiometers for Cosmic Microwave Background Site Characterization and Comparison
The compelling science case for the observation of B-mode polarization in the
cosmic microwave background (CMB) is driving the CMB community to expand the
observed sky fraction, either by extending survey sizes or by deploying
receivers to potential new northern sites. For ground-based CMB instruments,
poorly-mixed atmospheric water vapor constitutes the primary source of
short-term sky noise. This results in short-timescale brightness fluctuations,
which must be rejected by some form of modulation. To maximize the sensitivity
of ground-based CMB observations, it is useful to understand the effects of
atmospheric water vapor over timescales and angular scales relevant for CMB
polarization measurements. To this end, we have undertaken a campaign to
perform a coordinated characterization of current and potential future
observing sites using scanning 183 GHz water vapor radiometers (WVRs). So far,
we have deployed two identical WVR units; one at the South Pole, Antarctica,
and the other at Summit Station, Greenland. The former site has a long heritage
of ground-based CMB observations and is the current location of the Bicep/Keck
Array telescopes as well as the South Pole Telescope. The latter site, though
less well characterized, is under consideration as a northern-hemisphere
location for future CMB receivers. Data collection from this campaign began in
January 2016 at South Pole and July 2016 at Summit Station. Data analysis is
ongoing to reduce the data to a single spatial and temporal statistic that can
be used for one-to-one site comparison.Comment: Published in Proc. SPIE. Presented at SPIE Astronomical Telescopes
and Instrumentation Conference 10708: Millimeter, Submillimeter, and
Far-Infrared Detectors and Instrumentation for Astronomy XI, June 2018. 10
pages, 11 figure
Accelerator measurements of magnetically-induced radio emission from particle cascades with applications to cosmic-ray air showers
For fifty years, cosmic-ray air showers have been detected by their radio
emission. We present the first laboratory measurements that validate
electrodynamics simulations used in air shower modeling. An experiment at SLAC
provides a beam test of radio-frequency (RF) radiation from charged particle
cascades in the presence of a magnetic field, a model system of a cosmic-ray
air shower. This experiment provides a suite of controlled laboratory
measurements to compare to particle-level simulations of RF emission, which are
relied upon in ultra-high-energy cosmic-ray air shower detection. We compare
simulations to data for intensity, linearity with magnetic field, angular
distribution, polarization, and spectral content. In particular, we confirm
modern predictions that the magnetically induced emission in a dielectric forms
a cone that peaks at the Cherenkov angle and show that the simulations
reproduce the data within systematic uncertainties.Comment: 5 pages, 7 figure
Observational Constraints on the Ultra-high Energy Cosmic Neutrino Flux from the Second Flight of the ANITA Experiment
The Antarctic Impulsive Transient Antenna (ANITA) completed its second
long-duration balloon flight in January 2009, with 31 days aloft (28.5 live
days) over Antarctica. ANITA searches for impulsive coherent radio Cherenkov
emission from 200 to 1200 MHz, arising from the Askaryan charge excess in
ultra-high energy neutrino-induced cascades within Antarctic ice. This flight
included significant improvements over the first flight in the payload
sensitivity, efficiency, and a flight trajectory over deeper ice. Analysis of
in-flight calibration pulses from surface and sub-surface locations verifies
the expected sensitivity. In a blind analysis, we find 2 surviving events on a
background, mostly anthropogenic, of 0.97+-0.42 events. We set the strongest
limit to date for 1-1000 EeV cosmic neutrinos, excluding several current
cosmogenic neutrino models.Comment: 6 pages, 5 figures, submitted to Phys. Rev.
BICEP3: a 95 GHz refracting telescope for degree-scale CMB polarization
BICEP3 is a 550 mm-aperture refracting telescope for polarimetry of radiation
in the cosmic microwave background at 95 GHz. It adopts the methodology of
BICEP1, BICEP2 and the Keck Array experiments - it possesses sufficient
resolution to search for signatures of the inflation-induced cosmic
gravitational-wave background while utilizing a compact design for ease of
construction and to facilitate the characterization and mitigation of
systematics. However, BICEP3 represents a significant breakthrough in
per-receiver sensitivity, with a focal plane area 5 larger than a
BICEP2/Keck Array receiver and faster optics ( vs. ).
Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive
cold alumina filters and lenses were developed and implemented for its optics.
The camera consists of 1280 dual-polarization pixels; each is a pair of
orthogonal antenna arrays coupled to transition-edge sensor bolometers and read
out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15
season, BICEP3 will have survey speed comparable to Keck Array 150 GHz (2013),
and will significantly enhance spectral separation of primordial B-mode power
from that of possible galactic dust contamination in the BICEP2 observation
patch.Comment: 12 pages, 5 figures. Presented at SPIE Astronomical Telescopes and
Instrumentation 2014: Millimeter, Submillimeter, and Far-Infrared Detectors
and Instrumentation for Astronomy VII. To be published in Proceedings of SPIE
Volume 915
Observation of Ultra-high-energy Cosmic Rays with the ANITA Balloon-borne Radio Interferometer
We report the observation of sixteen cosmic ray events of mean energy of 1.5
x 10^{19} eV, via radio pulses originating from the interaction of the cosmic
ray air shower with the Antarctic geomagnetic field, a process known as
geosynchrotron emission. We present the first ultra-wideband, far-field
measurements of the radio spectral density of geosynchrotron emission in the
range from 300-1000 MHz. The emission is 100% linearly polarized in the plane
perpendicular to the projected geomagnetic field. Fourteen of our observed
events are seen to have a phase-inversion due to reflection of the radio beam
off the ice surface, and two additional events are seen directly from above the
horizon.Comment: 5 pages, 5 figures, new figure adde
- …