Search

Multispacecraft and multiwavelength observations of solar eruptions such as flares and coronal mass ejections are essential to understand the complex processes behind these events. The study of solar burst events in the radio-frequency spectrum has relied almost exclusively on data from ground-based radiotelescopes and dedicated heliophysics missions such as STEREO or Wind. Reanalysing existing data from the Mars Reconnaissance Orbiter (MRO) Shallow Radar (SHARAD) instrument, a Martian planetary radar sounder, we have detected 38 solar radio burst events with a correlated observation by at least one dedicated solar mission. The very high resolution of the instrument, both in temporal and frequency directions, its bandwidth, and its position in the solar system enable SHARAD to make significant contributions to heliophysics; it could inform on plasma processes on the site of the burst generation and also along the propagation path of associated fast electron beams. In this letter, we characterise the sensitivity of the instrument to type-III solar radio bursts through a statistical analysis of correlated observations, using STEREO and Wind as references. We establish the conditions under which SHARAD can observe solar bursts in terms of acquisition geometry, laying the foundation for its use as a solar radio-observatory. We also present the first analysis of type-III characteristic times at high resolution beyond 1 AU. The scaling laws are also comparable to results found on Earth, except for the fall time; a clearer distinction between fundamental and harmonic components of the bursts may be needed to resolve the discrepancy., Comment: 15 pages, 5 figures, 2 tables

The Beamforming Elevated Array for COsmic Neutrinos (BEACON) is a planned neutrino telescope designed to detect radio emission from upgoing air showers generated by ultrahigh energy tau neutrino interactions in the Earth. This detection mechanism provides a measurement of the tau flux of cosmic neutrinos. We have installed an 8-channel prototype instrument at high elevation at Barcroft Field Station, which has been running since 2018, and consists of 4 dual-polarized antennas sensitive between 30-80 MHz, whose signals are filtered, amplified, digitized, and saved to disk using a custom data acquisition system (DAQ). The BEACON prototype is at high elevation to maximize effective volume and uses a directional beamforming trigger to improve rejection of anthropogenic background noise at the trigger level. Here we discuss the design, construction, and calibration of the BEACON prototype instrument. We also discuss the radio frequency environment observed by the instrument, and categorize the types of events seen by the instrument, including a likely cosmic ray candidate event., 21 pages, 20 figures

Over the last several decades, radio detection of air showers has been widely used to detect ultra-high-energy cosmic rays. We developed an experiment under controlled laboratory conditions at SLAC with which we measured the radio-frequency radiation from a charged particle shower produced by bunches of electrons as primaries with known energy. The shower took place in a target made of High Density Polyethylene located in a strong magnetic field. The experiment was designed so that Askaryan and magnetically-induced components of the radio emission could be measured independently. At the same time, we performed a detailed simulation of this experiment to predict the radio signal using two microscopic formalisms, endpoint and ZHS. In this paper, we present the simulation scheme and make a comparison with data characteristics such as linearity with magnetic field and amplitude. The simulations agree with the measurements within uncertainties and present a good description of the data. In particular, reflections within the target that accounted for the largest systematic uncertainties are addressed. The prediction of the amplitude of Askaryan emission agrees with measurements to within 5% for the endpoint formalism and 11% for the ZHS formalism. The amplitudes of magnetically-induced emission agree to within 5% for the endpoint formalism and less than 1% for the ZHS formalism. The agreement of the absolute scale of emission gives confidence in state-of-the-art air shower simulations which are based on the applied formalisms.

We study in detail the sensitivity of the Antarctic Impulsive Transient Antenna (ANITA) to possible $\nu_\tau$ point source fluxes detected via $\tau$-lepton-induced air showers. This investigation is framed around the observation of four upward-going extensive air shower events very close to the horizon seen in ANITA-IV. We find that these four upgoing events are not observationally inconsistent with $\tau$-induced EASs from Earth-skimming $\nu_\tau$, both in their spectral properties as well as in their observed locations on the sky. These four events, as well as the overall diffuse and point source exposure to Earth-skimming $\nu_\tau$, are also compared against published ultrahigh-energy neutrino limits from the Pierre Auger Observatory. While none of these four events occurred at sky locations simultaneously visible by Auger, the implied fluence necessary for ANITA to observe these events is in strong tension with limits set by Auger across a wide range of energies and is additionally in tension with ANITA's Askaryan in-ice neutrino channel above $10^{19}$ eV. We conclude by discussing some of the technical challenges with simulating and analyzing these near horizon events and the potential for future observatories to observe similar events., Comment: 19 pages, 22 figures, will be published in Physical Review D (PRD)

We present a new technique to perform passive bistatic subsurface radar probes on airless planetary bodies. This technique uses the naturally occurring radio impulses generated when high-energy cosmic rays impact the body's surface. As in traditional radar sounding, the downward-beamed radio emission from each individual cosmic ray impact will reflect off subsurface dielectric contrasts and propagate back up to the surface to be detected. We refer to this technique as Askaryan radar after the fundamental physics process, the Askaryan effect, that produces this radio emission. This technique can be performed from an orbiting satellite, or from a surface lander, but since the radio emission is generated beneath the surface, an Askaryan radar can completely bypass the effects of surface clutter and backscatter typically associated with surface-penetrating radar. We present the background theory of Askaryan subsurface radar and show results from both finite-difference time-domain (FDTD) and Monte Carlo simulations that confirm that this technique is a promising planetary radar sounding method, producing detectable signals for realistic planetary science applications., Comment: 18 pages, 5 figures

Ultra-high-energy neutrinos serve as messengers of some of the highest energy astrophysical environments. Given that neutrinos are neutral and only interact via weak interactions, neutrinos can emerge from sources, traverse astronomical distances, and point back to their origins. Their weak interactions require large target volumes for neutrino detection. Using the Earth as a neutrino converter, terrestrial, sub-orbital, and satellite-based instruments are able to detect signals of neutrino-induced extensive air showers. In this paper, we describe the software code $\texttt{nuPyProp}$ that simulates tau neutrino and muon neutrino interactions in the Earth and predicts the spectrum of the $\tau$-lepton and muons that emerge. The $\texttt{nuPyProp}$ outputs are lookup tables of charged lepton exit probabilities and energies that can be used directly or as inputs to the $\texttt{nuSpaceSim}$ code designed to simulate optical and radio signals from extensive air showers induced by the emerging charged leptons. We describe the inputs to the code, demonstrate its flexibility and show selected results for $\tau$-lepton and muon exit probabilities and energy distributions. The $\texttt{nuPyProp}$ code is open source, available on Github., Comment: 42 pages, 21 figures, fixed typo in one of the author's name. Code available at https://github.com/NuSpaceSim/nupyprop

At any epoch, particle physics must be open to completely unexpected discoveries, and that is reason enough to extend the reach of searches for ultra-high energy (UHE) photons. The observation of a population of photons with energies $E \gtrsim 100$ EeV would for example imply the existence of either a completely new physical phenomena, or particle acceleration mechanisms heretofore never seen or imagined. But as we outline in this Letter of Interest, there are also good arguments for super-heavy dark matter (SHDM) in a parameter range such that it could be discovered via its decays to, in particular, UHE photons. Only ultra-high energy cosmic ray observatories have capabilities to detect UHE photons. We first investigate how current and future observations can probe and constrain SHDM models in important directions, and then outline some of the scenarios that motivate such searches. We also discuss connections between constraints on SHDM and on the parameter values of cosmological models., SNOWMASS 2021 LoI. Accepted for publication in Astroparticle Physics

The addition of an external starshade to the Nancy Grace Roman Space Telescope will enable the direct imaging of Earth-radius planets orbiting at ∼1 AU. Classification of any detected planets as Earth-like requires both spectroscopy to characterize their atmospheres and multi-epoch imaging to trace their orbits. We consider here the ability of the Starshade Rendezvous Probe to constrain the orbits of directly imaged Earth-like planets. The target list for this proposed mission consists of the 16 nearby stars best suited for direct imaging, around which ∼10 to 15 planets are expected to be discovered. Of these planets, ∼1 to 2 will be Earth-like in mass and temperature. The field of regard for the starshade mission is constrained by solar exclusion angles, resulting in four observing windows during a two-year mission. We find that for Earth-like planets that are detected at least three times during the four viewing opportunities, their semi-major axes are measured with a median precision of 7 mas, or a median fractional precision of 3%. Habitable-zone planets can be correctly identified as such 96.7% of the time, with a false positive rate of 2.8%. If a more conservative criteria are used for habitable-zone classification (95% probability), the false positive rate drops close to zero, but with only 81% of the truly Earth-like planets correctly classified as residing in the habitable zone.

The NASA supported High-Altitude Calibration (HiCal)-2 instrument flew as a companion balloon to the ANITA-4 experiment in December 2016. Based on a HV discharge pulser producing radio-frequency (RF) calibration pulses, HiCal-2 comprised two payloads, which flew for a combined 18 days, covering 1.5 revolutions of the Antarctic continent. ANITA-4 captured over 10,000 pulses from HiCal, both direct and reflected from the surface, at distances varying from 100-800 km, providing a large dataset for surface reflectivity measurements. Herein we present details on the design, construction and performance of HiCal-2., Comment: Published in NIM-A, final version

An array of low-frequency dipole antennas on the lunar farside surface will probe a unique, unexplored epoch in the early Universe called the Dark Ages. It begins at Recombination when neutral hydrogen atoms formed, first revealed by the cosmic microwave background. This epoch is free of stars and astrophysics, so it is ideal to investigate high energy particle processes including dark matter, early Dark Energy, neutrinos, and cosmic strings. A NASA-funded study investigated the design of the instrument and the deployment strategy from a lander of 128 pairs of antenna dipoles across a 10 kmx10 km area on the lunar surface. The antenna nodes are tethered to the lander for central data processing, power, and data transmission to a relay satellite. The array, named FARSIDE, would provide the capability to image the entire sky in 1400 channels spanning frequencies from 100 kHz to 40 MHz, extending down two orders of magnitude below bands accessible to ground-based radio astronomy. The lunar farside can simultaneously provide isolation from terrestrial radio frequency interference, the Earth's auroral kilometric radiation, and plasma noise from the solar wind. It is thus the only location within the inner solar system from which sky noise limited observations can be carried out at sub-MHz frequencies. Through precision calibration via an orbiting beacon and exquisite foreground characterization, the farside array would measure the Dark Ages global 21-cm signal at redshifts z~35-200. It will also be a pathfinder for a larger 21-cm power spectrum instrument by carefully measuring the foreground with high dynamic range., 14 pages, 3 figures, 1 table, response to DOE request for information on lunar farside radio telescope to explore the early universe. arXiv admin note: substantial text overlap with arXiv:1911.08649

Launching a starshade to rendezvous with the Nancy Grace Roman Space Telescope would provide the first opportunity to directly image the habitable zones of nearby sunlike stars in the coming decade. A report on the science and feasibility of such a mission was recently submitted to NASA as a probe study concept. The driving objective of the concept is to determine whether Earth-like exoplanets exist in the habitable zones of the nearest sunlike stars and have biosignature gases in their atmospheres. With the sensitivity provided by this telescope, it is possible to measure the brightness of zodiacal dust disks around the nearest sunlike stars and establish how their population compares to our own. In addition, known gas-giant exoplanets can be targeted to measure their atmospheric metallicity and thereby determine if the correlation with planet mass follows the trend observed in the Solar System and hinted at by exoplanet transit spectroscopy data. In this paper we provide the details of the calculations used to estimate the sensitivity of Roman with a starshade and describe the publicly available Python-based source code used to make these calculations. Given the fixed capability of Roman and the constrained observing windows inherent for the starshade, we calculate the sensitivity of the combined observatory to detect these three types of targets and we present an overall observing strategy that enables us to achieve these objectives., Accepted for publication in the Journal of Astronomical Telescopes, Instruments, and Systems (JATIS)

An accurate modeling of neutrino flux attenuation and the distribution of leptons they produce in transit through the Earth is an essential component to determine neutrino flux sensitivities of underground, sub-orbital and space-based detectors. Through neutrino oscillations over cosmic distances, astrophysical neutrino sources are expected to produce nearly equal fluxes of electron, muon and tau neutrinos. Of particular interest are tau neutrinos that interact in the Earth at modest slant depths to produce $��$-leptons. Some $��$-leptons emerge from the Earth and decay in the atmosphere to produce extensive air showers. Future balloon-borne and satellite-based optical Cherenkov neutrino telescopes will be sensitive to upward air showers from tau neutrino induced $��$-lepton decays. We present nuPyProp, a python code that is part of the nuSpaceSim package. nuPyProp generates look-up tables for exit probabilities and energy distributions for $��_��\to ��$ and $��_��\to ��$ propagation in the Earth. This flexible code runs with either stochastic or continuous electromagnetic energy losses for the lepton transit through the Earth. Current neutrino cross section models and energy loss models are included along with templates for user input of other models. Results from nuPyProp are compared with other recent simulation packages for neutrino and charged lepton propagation. Sources of modeling uncertainties are described and quantified., 9 pages, 6 figures, PoS(ICRC2021)1203; for associated code, see https://github.com/NuSpaceSim/nupyprop

The zodiacal dust complex, a population of dust and small particles that pervades the Solar System, provides important insight into the formation and dynamics of planets, comets, asteroids, and other bodies. Here we present a new set of data obtained using a novel technique: direct measurements of momentum transfer to a spacecraft from individual particle impacts. This technique is made possible by the extreme precision of the instruments flown on the LISA Pathfinder spacecraft, a technology demonstrator for a future space-based gravitational wave observatory that operated near the first Sun-Earth Lagrange point from early 2016 through Summer of 2017. Using a simple model of the impacts and knowledge of the control system, we show that it is possible to detect impacts and measure properties such as the transferred momentum (related to the particle's mass and velocity), direction of travel, and location of impact on the spacecraft. In this paper, we present the results of a systematic search for impacts during 4348 hours of Pathfinder data. We report a total of 54 candidates with momenta ranging from 0.2$\,\mu\textrm{Ns}$ to 230$\,\mu\textrm{Ns}$. We furthermore make a comparison of these candidates with models of micrometeoroid populations in the inner solar system including those resulting from Jupiter-family comets, Oort-cloud comets, Hailey-type comets, and Asteroids. We find that our measured population is consistent with a population dominated by Jupiter-family comets with some evidence for a smaller contribution from Hailey-type comets. This is in agreement with consensus models of the zodiacal dust complex in the momentum range sampled by LISA Pathfinder., Comment: 22 pages, 14 figures, accepted in ApJ

Air showers, produced by the interaction of energetic cosmic rays with the atmosphere, are an excellent alternative to study particle physics at energies beyond any human-made particle accelerator. For that, it is necessary to identify first the mass composition of the primary cosmic ray (and its energy). None of the existing high energy interaction models have been able to reproduce coherently all air shower observables over the entire energy and zenith angle phase space. This is despite having tried all possible combinations for the cosmic ray mass composition. This proposal outlines a self-consistent strategy to study high energy particle interactions and identify the energy spectra and mass composition of cosmic rays. This strategy involves the participation of different particle accelerators and astrophysics experiments. This is important to cover the entire cosmic ray energy range and a larger phase-space of shower observables to probe the high energy interaction models., Snowmass2021 - Letter of Interest

ANITA's fourth long-duration balloon flight in late 2016 detected 29 cosmic-ray (CR)-like events on a background of $0.37^{+0.27}_{-0.17}$ anthropogenic events. CRs are mainly seen in reflection off the Antarctic ice sheets, creating a characteristic phase-inverted waveform polarity. However, four of the below-horizon CR-like events show anomalous non-inverted polarity, a $p = 5.3 \times 10^{-4}$ chance if due to background. All anomalous events are from locations near the horizon; ANITA-IV observed no steeply-upcoming anomalous events similar to the two such events seen in prior flights., Comment: 6 pages, 4 figures, to appear in Physical Review Letters. Supplemental material (reference 17) available from corresponding author

We present a semi-analytical method for the calculation of coherent Askaryan radiation in showers induced by neutrinos of any flavor in ice. We compare our results with those of a full Monte Carlo simulation based on the ZHAireS code. This approach is able to reproduce the vector potential and hence electric field at any experimentally relevant observer position in the time domain. This work extends published results only valid for electron-induced showers. We establish the validity of the semi-analytical calculation of the radio signal produced by all types of neutrino-induced showers in ice. The method is computationally efficient and only requires as inputs the longitudinal charge excess profile of the showers and a parameterization of the vector potential in the far-field region of the shower at the Cherenkov angle that we also provide. Our methodology avoids tracking the contributions to the electric field from millions of particles every time the radio pulse has to be calculated at a given observer position. These results can be readily used in the interpretation of the data taken by experiments, and in the planning and design of future initiatives based on the radio technique in ice., 18 pages, 11 figures. Accepted in Phys. Rev. D

The ANITA balloon experiment was designed to detect radio signals initiated by neutrinos and cosmic ray air showers. These signals are typically discriminated by the polarization and phase inversions of the radio signal. The reflected signal from cosmic rays suffer phase inversion compared to a direct tau neutrino event. In this paper we study sub-surface reflection, which can occur without phase inversion, in the context of the two anomalous up-going events reported by ANITA. We find that subsurface layers and firn density inversions may plausibly account for the events, while ice fabric layers and wind ablation crusts could also play a role. This hypothesis can be tested with radar surveying of the Antarctic region in the vicinity of the anomalous ANITA events. Future experiments should not use phase inversion as a sole criterion to discriminate between downgoing and upgoing events, unless the subsurface reflection properties are well understood., 4+2 pages, 3 figures

High-energy astrophysical neutrinos, recently discovered by IceCube up to energies of several PeV, opened a new window to the high-energy Universe. Yet much remains to be known. IceCube has excellent muon flavor identification, but tau flavor identification is challenging. This limits its ability to probe neutrino physics and astrophysics. To address this limitation, we present a concept for a large-scale observatory of astrophysical tau neutrinos in the 1-100 PeV range, where a flux is guaranteed to exist. Its detection would allow us to characterize the neutrino sources observed by IceCube, to discover new ones, and test neutrino physics at high energies. The deep-valley air-shower array concept that we present provides highly background-suppressed neutrino detection with pointing resolution, 15 pages, 6 figures, white paper submitted to the Latin American Strategy Forum for Research Infrastructure (LASF4RI)

The ANtarctic Impulsive Transient Antenna (ANITA) long-duration balloon experiment is sensitive to interactions of ultra high-energy (E > 10^{18} eV) neutrinos in the Antarctic ice sheet. The third flight of ANITA, lasting 22 days, began in December 2014. We develop a methodology to search for energetic neutrinos spatially and temporally coincident with potential source classes in ANITA data. This methodology is applied to several source classes: the TXS 0506+056 blazar and NGC 1068, the first potential TeV neutrino sources identified by IceCube, flaring high-energy blazars reported by the Fermi All-Sky Variability Analysis, gamma-ray bursts, and supernovae. Among searches within the five source classes, one candidate was identified as associated with SN 2015D, although not at a statistically significant level. We proceed to place upper limits on the source classes. We further comment on potential applications of this methodology to more sensitive future instruments., 23 pages, 7 figures, version accepted to JCAP

Tau neutrinos are expected to comprise roughly one third of both the astrophysical and cosmogenic neutrino flux, but currently the flavor ratio is poorly constrained and the expected flux at energies above $10^{17}$ eV is low. We present a detector concept aimed at measuring the diffuse flux of tau neutrinos in this energy range via a high-elevation mountaintop detector using the radio technique. The detector searches for radio signals from upgoing air showers generated by Earth-skimming tau neutrinos. Signals from several antennas in a compact array are coherently summed at the trigger level, permitting not only directional masking of anthropogenic backgrounds, but also a low trigger threshold. This design takes advantage of both the large viewing area available at high-elevation sites and the nearly full duty cycle available to radio instruments. We present trade studies that consider the station elevation, frequency band, number of antennas in the array, and the trigger threshold to develop a highly efficient station design. Such a mountaintop detector can achieve a factor of ten improvement in acceptance over existing instruments with 100 independent stations. With 1000 stations and three years of observation, it can achieve a sensitivity to an integrated $\mathcal{E}^{-2}$ flux of $, 26 pages, 11 figures

The Payload for Ultrahigh Energy Observations (PUEO) long-duration balloon experiment is designed to have world-leading sensitivity to ultrahigh-energy neutrinos at energies above 1 EeV. Probing this energy region is essential for understanding the extreme-energy universe at all distance scales. PUEO leverages experience from and supersedes the successful Antarctic Impulsive Transient Antenna (ANITA) program, with an improved design that drastically improves sensitivity by more than an order of magnitude at energies below 30 EeV. PUEO will either make the first significant detection of or set the best limits on ultrahigh-energy neutrino fluxes., Comment: 40 pages, 17 figures. Version accepted to JINST

Recently, the ANITA collaboration reported on two upward-going extensive air shower events consistent with a primary particle that emerges from the surface of the ice. These events may be of $\nu_\tau$ origin, in which the neutrino interacts within the Earth to produce a $\tau$ lepton that emerges from the Earth, decays in the atmosphere, and initiates an extensive air shower. In this paper we estimate an upper bound on the ANITA acceptance to a diffuse $\nu_\tau$ flux detected via $\tau$-lepton-induced air showers within the bounds of Standard Model (SM) uncertainties. By comparing this estimate with the acceptance of Pierre Auger Observatory and IceCube and assuming SM interactions, we conclude that a $\nu_\tau$ origin of these events would imply a neutrino flux at least two orders of magnitude above current bounds., Comment: 12 pages, 7 figures

The ANtarctic Impulsive Transient Antenna (ANITA) NASA long-duration balloon payload completed its fourth flight in December 2016, after 28 days of flight time. ANITA is sensitive to impulsive broadband radio emission from interactions of ultra-high-energy neutrinos in polar ice (Askaryan emission). We present the results of two separate blind analyses searching for signals from Askaryan emission in the data from the fourth flight of ANITA. The more sensitive analysis, with a better expected limit, has a background estimate of $0.64^{+0.69}_{-0.45}$ and an analysis efficiency of $82\pm2\%$. The second analysis has a background estimate of $0.34^{+0.66}_{-0.16}$ and an analysis efficiency of $71\pm6\%$. Each analysis found one event in the signal region, consistent with the background estimate for each analysis. The resulting limit further tightens the constraints on the diffuse flux of ultra-high-energy neutrinos at energies above $10^{19.5}$ eV., 11 pages, 7 figures

FARSIDE (Farside Array for Radio Science Investigations of the Dark ages and Exoplanets) is a Probe-class concept to place a low radio frequency interferometric array on the farside of the Moon. A NASA-funded design study, focused on the instrument, a deployment rover, the lander and base station, delivered an architecture broadly consistent with the requirements for a Probe mission. This notional architecture consists of 128 dual polarization antennas deployed across a 10 km area by a rover, and tethered to a base station for central processing, power and data transmission to the Lunar Gateway. FARSIDE would provide the capability to image the entire sky each minute in 1400 channels spanning frequencies from 100 kHz to 40 MHz, extending down two orders of magnitude below bands accessible to ground-based radio astronomy. The lunar farside can simultaneously provide isolation from terrestrial radio frequency interference, auroral kilometric radiation, and plasma noise from the solar wind. This would enable near-continuous monitoring of the nearest stellar systems in the search for the radio signatures of coronal mass ejections and energetic particle events, and would also detect the magnetospheres for the nearest candidate habitable exoplanets. Simultaneously, FARSIDE would be used to characterize similar activity in our own solar system, from the Sun to the outer planets, including the hypothetical Planet Nine. Through precision calibration via an orbiting beacon, and exquisite foreground characterization, FARSIDE would also measure the Dark Ages global 21-cm signal at redshifts z=50-100. The unique observational window offered by FARSIDE would enable an abundance of additional science ranging from sounding of the lunar subsurface to characterization of the interstellar medium in the solar system neighborhood., Comment: 13 pages, 9 figures, 2 tables, Astro2020 Decadal Survey whitepaper

We report an error found during independent review of the NuTauSim publicly available code \url{https://github.com/harmscho/NuTauSim} that forms the basis of this publication. The error in the code was in tracking the density of the medium during particle propagation. After the first interaction, the code was referencing the depth of penetration back to the surface of the Earth rather than the location of the last interaction. The results were obtained using densities that were systematically underestimated when the particle was traversing the inner layers of the Earth by assigning the density of either ice or bedrock, depending on the particle energy or ice thickness of the simulation. This error was fixed and the repository updated on September 29, 2018., Comment: erratum to arXiv:1707.00334

Bulletin of the American Astronomical Society 51, 215 (2019)., High-energy cosmic neutrinos can reveal new fundamental particles and interactions, probing energy and distance scales far exceeding those accessible in the laboratory. This white paper describes the outstanding particle physics questions that high-energy cosmic neutrinos can address in the coming decade. A companion white paper discusses how the observation of cosmic neutrinos can address open questions in astrophysics. Tests of fundamental physics using high-energy cosmic neutrinos will be enabled by detailed measurements of their energy spectrum, arrival directions, flavor composition, and timing., Published by American Institute of Physics (AIP), New York, NY

This is the final report submitted to NASA for a Probe-class concept study of the "Farside Array for Radio Science Investigations of the Dark ages and Exoplanets" (FARSIDE), a low radio frequency interferometric array on the farside of the Moon. The design study focused on the instrument, a deployment rover, the lander and base station, and delivered an architecture broadly consistent with the requirements for a Probe mission. This notional architecture consists of 128 dipole antennas deployed across a 10 km area by a rover, and tethered to a base station for central processing, power and data transmission to the Lunar Gateway, or an alternative relay satellite. FARSIDE would provide the capability to image the entire sky each minute in 1400 channels spanning frequencies from 150 kHz to 40 MHz, extending down two orders of magnitude below bands accessible to ground-based radio astronomy. The lunar farside can simultaneously provide isolation from terrestrial radio frequency interference, auroral kilometric radiation, and plasma noise from the solar wind. This would enable near-continuous monitoring of the nearest stellar systems in the search for the radio signatures of coronal mass ejections and energetic particle events, and would also detect the magnetospheres for the nearest candidate habitable exoplanets. Simultaneously, FARSIDE would be used to characterize similar activity in our own solar system, from the Sun to the outer planets. Through precision calibration via an orbiting beacon, and exquisite foreground characterization, FARSIDE would also measure the Dark Ages global 21-cm signal at redshifts from 50-100. It will also be a pathfinder for a larger 21-cm power spectrum instrument by carefully measuring the foreground with high dynamic range., Comment: 50 pages, NASA Probe final study report. arXiv admin note: text overlap with arXiv:1907.05407

A Monte Carlo simulation program for the radio detection of Ultra High Energy (UHE) neutrino interactions in the Antarctic ice as viewed by the Antarctic Impulsive Transient Antenna (ANITA) is described in this article. The program, icemc, provides an input spectrum of UHE neutrinos, the parametrization of the Askaryan radiation generated by their interaction in the ice, and the propagation of the radiation through ice and air to a simulated model of the third and fourth ANITA flights. This paper provides an overview of the icemc simulation, descriptions of the physics models used and of the ANITA electronics processing chain, data/simulation comparisons to validate the predicted performance, and a summary of the impact of published results.

A successful ground array Radio Frequency (RF)-only self-trigger is demonstrated with 256 dual-polarization antennas of the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), yielding 10 high-energy cosmic ray candidates. This RF-only capability is predicated on novel techniques for Radio Frequency Interference (RFI) identification and mitigation with an analysis efficiency of approximately 45% for shower-driven events with a Signal-to-noise ratio ≳ 5 against the galactic background noise power of individual antennas. Radio self-triggering enables more efficient detection of cosmic rays over a wider range of zenith angles than possible via triggers from in-situ particle detectors and the method presented here can be easily adapted to neutrino experiments relying on RF-only detection. This paper discusses the system design, RFI characterization and mitigation techniques, and initial results from 10 cosmic ray candidate events identified within a 40-hour observing window. A design for a future optimized commensal cosmic-ray detector for the OVRO-LWA is presented, as well as recommendations for developing a similar capability for other experiments — these designs either reduce data-rate or increase sensitivity by an order of magnitude for many configurations of radio instruments.

We report on an upward traveling, radio-detected cosmic-ray-like impulsive event with characteristics closely matching an extensive air shower. This event, observed in the third flight of the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload, is consistent with a similar event reported in a previous flight. These events may be produced by the atmospheric decay of an upward-propagating $\tau$-lepton produced by a $\nu_{\tau}$ interaction, although their relatively steep arrival angles create tension with the standard model (SM) neutrino cross section. Each of the two events have $a~posteriori$ background estimates of $\lesssim 10^{-2}$ events. If these are generated by $\tau$-lepton decay, then either the charged-current $\nu_{\tau}$ cross section is suppressed at EeV energies, or the events arise at moments when the peak flux of a transient neutrino source was much larger than the typical expected cosmogenic background neutrinos., Comment: 5 pages, 4 figures. Supplemental material available from corresponding author by request

The Antarctic Impulsive Transient Antenna (ANITA), a NASA long-duration balloon payload, searches for radio emission from interactions of ultra-high-energy neutrinos in polar ice. The third flight of ANITA (ANITA-III) was launched in December 2014 and completed a 22-day flight. We present the results of three analyses searching for Askaryan radio emission of neutrino origin. In the most sensitive of the analyses, we find one event in the signal region on an expected a priori background of $0.7^{+0.5}_{-0.3}$. Though consistent with the background estimate, the candidate event remains compatible with a neutrino hypothesis even after additional post-unblinding scrutiny., Comment: 15 pages, 15 figures, Accepted to PRD

The Space Technology 7 Disturbance Reduction System (ST7-DRS) is a NASA technology demonstration payload that operated from January 2016 through July of 2017 on the European Space Agency's LISA Pathfinder spacecraft. The joint goal of the NASA and ESA missions was to validate key technologies for a future space-based gravitational wave observatory targeting the source-rich milliHertz band. The two primary components of ST7-DRS are a micropropulsion system based on colloidal micro-Newton thrusters (CMNTs) and a control system that simultaneously controls the attitude and position of the spacecraft and the two free-flying test masses (TMs). This paper presents our main experimental results and summarizes the overall the performance of the CMNTs and control laws. We find that the CMNT performance to be consistent with pre-flight predictions, with a measured system thrust noise on the order of $100\,\textrm{nN}/\sqrt{\textrm{Hz}}$ in the $1\,\textrm{mHz}\leq f \leq 30\,\textrm{mHz}$ band. The control system maintained the TM-spacecraft separation with an RMS error of less than 2$\,$nm and a noise spectral density of less than $3\,\textrm{nm}/\sqrt{\textrm{Hz}}$ in the same band. Thruster calibration measurements yield thrust values consistent with the performance model and ground-based thrust-stand measurements, to within a few percent. We also report a differential acceleration noise between the two test masses with a spectral density of roughly $3\,\textrm{fm}/\textrm{s}^2/\sqrt{\textrm{Hz}}$ in the $1\,\textrm{mHz}\leq f \leq 30\,\textrm{mHz}$ band, slightly less than twice as large as the best performance reported with the baseline LISA Pathfinder configuration and below the current requirements for the Laser Interferometer Space Antenna (LISA) mission.

The balloon-borne HiCal radio-frequency (RF) transmitter, in concert with the ANITA radio-frequency receiver array, is designed to measure the Antarctic surface reflectivity in the RF wavelength regime. The amplitude of surface-reflected transmissions from HiCal, registered as triggered events by ANITA, can be compared with the direct transmissions preceding them by O(10) microseconds, to infer the surface power reflection coefficient $\cal{R}$. The first HiCal mission (HiCal-1, Jan. 2015) yielded a sample of 100 such pairs, resulting in estimates of $\cal{R}$ at highly-glancing angles (i.e., zenith angles approaching $90^\circ$), with measured reflectivity for those events which exceeded extant calculations. The HiCal-2 experiment, flying from Dec., 2016-Jan., 2017, provided an improvement by nearly two orders of magnitude in our event statistics, allowing a considerably more precise mapping of the reflectivity over a wider range of incidence angles. We find general agreement between the HiCal-2 reflectivity results and those obtained with the earlier HiCal-1 mission, as well as estimates from Solar reflections in the radio-frequency regime. In parallel, our calculations of expected reflectivity have matured; herein, we use a plane-wave expansion to estimate the reflectivity R from both a flat, smooth surface (and, in so doing, recover the Fresnel reflectivity equations) and also a curved surface. Multiplying our flat-smooth reflectivity by improved Earth curvature and surface roughness corrections now provides significantly better agreement between theory and the HiCal 2a/2b measurements., Comment: submitted to Astropart. Phys

The primary science goal of the NASA-sponsored ANITA project is measurement of ultra-high energy neutrinos and cosmic rays, observed via radio-frequency signals resulting from a neutrino- or cosmic ray- interaction with terrestrial matter (atmospheric or ice molecules, e.g.). Accurate inference of the energies of these cosmic rays requires understanding the transmission/reflection of radio wave signals across the ice-air boundary. Satellite-based measurements of Antarctic surface reflectivity, using a co-located transmitter and receiver, have been performed more-or-less continuously for the last few decades. Satellite-based reflectivity surveys, at frequencies ranging from 2--45 GHz and at near-normal incidence, yield generally consistent reflectivity maps across Antarctica. Using the Sun as an RF source, and the ANITA-3 balloon borne radio-frequency antenna array as the RF receiver, we have also measured the surface reflectivity over the interval 200-1000 MHz, at elevation angles of 12-30 degrees, finding agreement with the Fresnel equations within systematic errors. To probe low incidence angles, inaccessible to the Antarctic Solar technique and not probed by previous satellite surveys, a novel experimental approach ("HiCal-1") was devised. Unlike previous measurements, HiCal-ANITA constitute a bi-static transmitter-receiver pair separated by hundreds of kilometers. Data taken with HiCal, between 200--600 MHz shows a significant departure from the Fresnel equations, constant with frequency over that band, with the deficit increasing with obliquity of incidence, which we attribute to the combined effects of possible surface roughness, surface grain effects, radar clutter and/or shadowing of the reflection zone due to Earth curvature effects., updated to match publication version

There has been a recent surge in interest in the detection of $\tau$ lepton-induced air showers from detectors at altitude. When a $\tau$ neutrino ($\nu_\tau$) enters the Earth it produces $\tau$ leptons as a result of nuclear charged current interactions. In some cases, this process results in a $\tau$ lepton exiting the surface of the Earth, which can subsequently decay in the atmosphere and produce an extensive air shower. These upward-going air showers can be detected via fluorescence, optical Cherenkov, or geomagnetic radio emission. Several experiments have been proposed to detect these signals. We present a comprehensive simulation of the production of $\tau$ leptons by $\nu_\tau$'s propagating through Earth to aid the design of future experiments. These simulations for $\nu_\tau$'s and leptons in the energy range from $10^{15}$ eV to $10^{21}$ eV treat the full range of incidence angles from Earth-skimming to diametrically-traversing. Propagation of $\nu_\tau$'s and leptons include the effects of rock and an ocean or ice layer of various thicknesses. The interaction models include $\nu_\tau$ regeneration and account for uncertainties in the Standard Model neutrino cross-section and in the photo-nuclear contribution to the $\tau$ energy loss rate., Comment: 13 pages, 14 figures

The Antarctic Impulsive Transient Antenna (ANITA) is a NASA long-duration balloon experiment with the primary goal of detecting ultra-high-energy ($>10^{18}\,\mbox{eV}$) neutrinos via the Askaryan Effect. The fourth ANITA mission, ANITA-IV, recently flew from Dec 2 to Dec 29, 2016. For the first time, the Tunable Universal Filter Frontend (TUFF) boards were deployed for mitigation of narrow-band, anthropogenic noise with tunable, switchable notch filters. The TUFF boards also performed second-stage amplification by approximately 45 dB to boost the $\sim\,��\mbox{V-level}$ radio frequency (RF) signals to $\sim$ mV-level for digitization, and supplied power via bias tees to the first-stage, antenna-mounted amplifiers. The other major change in signal processing in ANITA-IV is the resurrection of the $90^{\circ}$ hybrids deployed previously in ANITA-I, in the trigger system, although in this paper we focus on the TUFF boards. During the ANITA-IV mission, the TUFF boards were successfully operated throughout the flight. They contributed to a factor of 2.8 higher total instrument livetime on average in ANITA-IV compared to ANITA-III due to reduction of narrow-band, anthropogenic noise before a trigger decision is made., 27 pages, 19 figures

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., 13 Pages, 14 Figures

We report on four radio-detected cosmic-ray (CR) or CR-like events observed with the Antarctic Impulsive Transient Antenna (ANITA), a NASA-sponsored long-duration balloon payload. Two of the four were previously identified as stratospheric CR air showers during the ANITA-I flight. A third stratospheric CR was detected during the ANITA-II flight. Here we report on characteristics these three unusual CR events, which develop nearly horizontally, 20-30~km above the surface of the Earth. In addition, we report on a fourth steeply upward-pointing ANITA-I CR-like radio event which has characteristics consistent with a primary that emerged from the surface of the ice. This suggests a possible $\tau$-lepton decay as the origin of this event, but such an interpretation would require significant suppression of the Standard Model ${\tau}$-neutrino cross section., Comment: 5pp,4 figures, referees' comments addressed, this version accepted to Phys. Rev. Letters. Supplemental PDF material available; see source files

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., 5 pages, 7 figures

We estimate the sensitivity of a lander-based instrument for the passive radio detection of a subsurface ocean beneath the ice shell of Europa, expected to be between 3~km - 30~km thick, using Jupiter's decametric radiation. A passive technique was previously studied for an orbiter. Using passive detection in a lander platform provides a point measurement with significant improvements due to largely reduced losses from surface roughness effects, longer integration times, and diminished dispersion due to ionospheric effects allowing operation at lower frequencies and a wider band. A passive sounder on-board a lander provides a low resource instrument sensitive to subsurface ocean at Europa up to depths of 6.9~km for high loss ice (16 dB/km two-way attenuation rate) and 69~km for pure ice (1.6 dB/km)., Comment: 5 pages, 2 figures

A flux of extra-terrestrial neutrinos at energies $\gg10^{15}$ eV has the potential to serve as a cosmological probe of the high-energy universe as well as tests of fundamental particle interactions. Cosmogenic neutrinos, produced from the interactions of ultra-high energy cosmic rays (UHECRs) with cosmic photon backgrounds, have been regarded as a guaranteed flux. However, the expected neutrino flux depends on the composition of UHECRs at the highest energies; heavier nuclei result in lower neutrino fluxes compared to lighter nuclei and protons. The objective of this study is to estimate the range of cosmogenic neutrino spectra consistent with recent cosmic-ray spectral and compositional data using a fully inferential Bayesian approach. The study assumes a range of source distributions consistent with astrophysical sources, the flux and composition of cosmic rays, and detector systematic uncertainties. The technique applied to this study is the use of an affine-invariant Markov Chain Monte Carlo, which is an effective Bayesian inference tool for characterizing multi-dimensional parameter spaces and their correlations., Comment: 28 pages, 6 figures

Recent analyses of cosmic ray arrival directions have resulted in evidence for a positive correlation with active galactic nuclei positions that has weak significance against an isotropic source distribution. In this paper, we explore the sample size needed to measure a highly statistically significant correlation to a parent source catalogue. We compare several scenarios for the directional scattering of ultra-high energy cosmic rays given our current knowledge of the galactic and intergalactic magnetic fields. We find significant correlations are possible for a sample of $>$1000 cosmic ray protons with energies above 60 EeV., 23 pages, 9 figures

We present an interferometric technique for the reconstruction of ultra-wide band impulsive signals from point sources. This highly sensitive method was developed for the search for ultra-high energy neutrinos with the ANITA experiment but is fully generalizable to any antenna array detecting radio impulsive events. Applications of the interferometric method include event reconstruction, thermal noise and anthropogenic background rejection, and solar imaging for calibrations. We illustrate this technique with applications from the analysis of the ANITA-I and ANITA-II data in the 200-1200 MHz band., 27 pages and 16 figures

We present a concept for on-orbit radio detection of ultra-high energy cosmic rays (UHECRs) that has the potential to provide collection rates of ~100 events per year for energies above 10^20 eV. The synoptic wideband orbiting radio detector (SWORD) mission's high event statistics at these energies combined with the pointing capabilities of a space-borne antenna array could enable charged particle astronomy. The detector concept is based on ANITA's successful detection UHECRs where the geosynchrotron radio signal produced by the extended air shower is reflected off the Earth's surface and detected in flight., 29 pages, 25 figures

From an elevation of ~38 km, the balloon-borne ANtarctic Impulsive Transient Antenna (ANITA) is designed to detect the up-coming radio frequency (RF) signal resulting from a sub-surface neutrino-nucleon collision. Although no neutrinos have been discovered thus far, ANITA is nevertheless the only experiment to self-trigger on radio frequency emissions from cosmic-ray induced atmospheric air showers. In the majority of those cases, down-coming RF signals are observed via their reflection from the Antarctic ice sheet and back up to the ANITA interferometer. Estimating the energy scale of the incident cosmic rays therefore requires an estimate of the fractional power reflected at the air-ice interface. Similarly, inferring the energy of neutrinos interacting in-ice from observations of the upwards-directed signal refracting out to ANITA also requires consideration of signal coherence across the interface. By comparing the direct Solar RF signal intensity measured with ANITA to the surface-reflected Solar signal intensity, as a function of incident elevation angle relative to the surface {\Theta}, we estimate the power reflection coefficients R({\Theta}). We find general consistency between our average measurements and the values of R({\Theta}) expected from the Fresnel equations, separately for horizontal- vs. vertical-polarizations., Comment: final version as accepted for publication by Radio Science

Using detailed Monte Carlo simulations we have characterized the features of the radio emission of inclined air showers in the Ultra-High Frequency band (300 MHz - 3 GHz). The Fourier-spectrum of the radiation is shown to have a sizable intensity well into the GHz frequency range. The emission is mainly due to transverse currents induced by the geomagnetic field and to the excess charge produced by the Askaryan effect. At these frequencies only a significantly reduced volume of the shower around the axis contributes coherently to the signal observed on the ground. The size of the coherently emitting volume depends on frequency, shower geometry and observer position, and is interpreted in terms of the relative time delays. At ground level, the maximum emission at high frequencies is concentrated in an elliptical ring-like region around the intersection of a Cherenkov cone with its vertex at shower maximum and the ground. The frequency spectrum of inclined showers when observed at positions that view shower maximum in the Cherenkov direction, is shown to be in broad agreement with the pulses detected by the Antarctic Impulsive Transient Antenna (ANITA) experiment, making the interpretation that they are due to Ultra-High Energy Cosmic Ray atmospheric showers consistent with our simulations. These results are also of great importance for experiments aiming to detect molecular bremsstrahlung radiation in the GHz range as they present an important background for its detection., 8 pages, 8 figures

The detection of high energy neutrinos ($10^{15}-10^{20}$ eV or $1-10^{5}$ PeV) is an important step toward understanding the most energetic cosmic accelerators and would enable tests of fundamental physics at energy scales that cannot easily be achieved on Earth. In this energy range, there are two expected populations of neutrinos: the astrophysical flux observed with IceCube at lower energies ($\sim1$ PeV) and the predicted cosmogenic flux at higher energies ($\sim10^{18}$ eV). Radio detector arrays such as RICE, ANITA, ARA, and ARIANNA exploit the Askaryan effect and the radio transparency of glacial ice, which together enable enormous volumes of ice to be monitored with sparse instrumentation. We describe here the design for a phased radio array that would lower the energy threshold of radio techniques to the PeV scale, allowing measurement of the astrophysical flux observed with IceCube over an extended energy range. Meaningful energy overlap with optical Cherenkov telescopes could be used for energy calibration. The phased radio array design would also provide more efficient coverage of the large effective volume required to discover cosmogenic neutrinos., Comment: 21 pages, 10 figures

Searches for radio signatures of ultra-high energy neutrinos and cosmic rays could benefit from improved efficiency by using real-time beamforming or correlation triggering. For missions with power limitations, such as the ANITA-3 Antarctic balloon experiment, full speed high resolution digitization of incoming signals is not practical. To this end, the University of Hawaii has developed the Realtime Independent Three-bit Converter (RITC), a 3-channel, 3-bit, streaming analog-to-digital converter implemented in the IBM-8RF 0.13 um process. RITC is primarily designed to digitize broadband radio signals produced by the Askaryan effect, and thus targets an analog bandwidth of >1 GHz, with a sample-and-hold architecture capable of storing up to 2.6 gigasamples-per-second. An array of flash analog-to-digital converters perform 3-bit conversion of sets of stored samples while acquisition continues elsewhere in the sampling array. A serial interface is provided to access an array of on chip digital-to-analog converters that control the digitization thresholds for each channel as well as the overall sampling rate. Demultiplexed conversion outputs are read out simultaneously for each channel via a set of 36 LVDS links, each running at 650 Mb/s. We briefly describe the design architecture of RITC. Evaluation of the RITC is currently under way, and we will report testing updates as they become available, including prospects for the use of this architecture as the analog half of a novel triggering system for the ANITA-3 ultra-high energy neutrino experiment., 3 pages, 5 figures

The detection of electromagnetic pulses from high energy showers is used as a means to search for Ultra-High Energy cosmic ray and neutrino interactions. An approximate formula has been obtained to numerically evaluate the radio pulse emitted by a charged particle that instantaneously accelerates, moves at constant speed along a straight track and halts again instantaneously. The approximate solution is applied to the particle track after dividing it in smaller subintervals. The resulting algorithm (often referred to as the ZHS algorithm) is also the basis for most of the simulations of the electric field produced in high energy showers in dense media. In this work, the electromagnetic pulses as predicted with the ZHS algorithm are compared to those obtained with an exact solution of the electric field produced by a charged particle track. The precise conditions that must apply for the algorithm to be valid are discussed and its accuracy is addressed. This comparison is also made for electromagnetic showers in dense media. The ZHS algorithm is shown to describe Cherenkov radiation and to be valid for most situations of interest concerning detectors searching for Ultra-High Energy neutrinos. The results of this work are also relevant for the simulation of pulses emitted from air showers., Comment: 12 pages, 7 figures

An in-depth characterization of coherent radio Cherenkov pulses from particle showers in dense dielectric media, referred to as the Askaryan effect, is presented. The time-domain calculation developed in this article is based on a form factor to account for the lateral dimensions of the shower. It is computationally efficient and able to reproduce the results of detailed particle shower simulations with high fidelity in most regions of practical interest including Fresnel effects due to the longitudinal development of the shower. In addition, an intuitive interpretation of the characteristics of the Askaryan pulse is provided. We expect our approach to benefit the analysis of radio pulses in experiments exploiting the radio technique., Replaced with version published Phys. Rev. D