arXiv subjects

A. Nelles

Publications and source records attributed to A. Nelles.

At least 19 recordsLinked to original sources

arXiv2026

The beamformed trigger of RNO-G: its design and in-field performance

The Radio Neutrino Observatory in Greenland (RNO-G) is a neutrino detector under construction at Summit Station, with 8 out of a planned 35 stations currently deployed. We have designed and deployed a new phased array (PA) trigger based on delay-and-sum beamforming and power integration. This trigger improves detector performance by suppressing thermal noise and better targeting neutrino-induced Askaryan signals. The new PA trigger has been deployed since the 2025 season. The trigger performance has been characterized using test pulses and calibration pulsers both in the lab and in-situ, and we find across these tests a 25% average reduction in the signal-to-noise ratio (SNR) needed to trigger on signals. Simulations are shown to be representative of the detector, and simulated trigger efficiencies are within 10% of measured data. Following the in-situ trigger validation, we use data-driven trigger performance to inform simulations of the detector effective volumes. The PA trigger increases our effective volume significantly, by over a factor of 2 below 0.1 EeV and at least a factor of 1.3 at the highest energies of 100 EeV.

astro-ph.IM↗

arXiv2026

Origins of Cosmic Rays in the Galactic-extragalactic Transition Energy Range

Cosmic rays arrive at Earth with energies ranging from $10^9$ to over $10^{20}$ eV. One of the open questions in high-energy cosmic ray science concerns the origin of the highest-energy cosmic rays that can be accelerated by Galactic sources, and the transition energy beyond which only extragalactic sources can provide. Measuring the mass composition gives essential information for comparing measurements to source and propagation models, both from the abundances at the source and from the maximum attainable energy which is proportional to the particle charge (and hence its mass). The highest-energy cosmic rays from the Galaxy are found in a range of $10^{16}$ to $10^{18}$ eV which is well suited for radio detection. Building on a decade of experience in measuring cosmic rays at LOFAR, we show that SKA-Low, augmented with an array of small particle detectors, is well suited to advance the field by measuring the mass composition of cosmic rays across this energy range.

astro-ph.HE↗

arXiv2025

Validating the performance of the Radio Neutrino Observatory in Greenland using cosmic-ray air showers

The Radio Neutrino Observatory in Greenland (RNO-G) is currently under construction with the aim to detect neutrinos with energies beyond $\sim 10\,\mathrm{PeV}$. A critical part of early detector commissioning is the study of detector characteristics and potential backgrounds, for which cosmic rays play a crucial role. In this article, we report that the number of cosmic rays detected with RNO-G's shallow antennas is consistent with expectations. We further verified the agreement in the observed cosmic-ray signal shape with expectations from simulations after careful treatment of the detector systematics. Finally, we find that the reconstructed arrival direction, energy, and polarization of the cosmic-ray candidates agrees with expectations. Throughout this study, we identified detector shortcomings that are mitigated going forward. Overall, the analysis presented here is an essential first step towards validating the detector and high-fidelity neutrino detection with RNO-G in the future.

astro-ph.HE↗

arXiv2025

Investigating double bump air showers with the SKA-Low

Double-bump showers are a rare class of extensive air showers (EAS) predicted by Monte Carlo simulations. They occur when a high-energy secondary particle, the leading particle, travels significantly farther than the rest, creating a distinct double-peaked longitudinal profile. So far, no experiment has been able to directly detect these showers. The unique radio footprint of double-bump showers, characterized by multiple Cherenkov rings, provides a way to reconstruct longitudinal profiles from radio observations. With its dense antenna array and broad frequency range, the Square Kilometer Array Observatory (SKAO) will be the first experiment capable of detecting these features, offering a new opportunity to probe hadronic interactions and constrain particle cross sections at high energies. In our analysis, we simulate the EAS using CORSIKA with the CoREAS plugin for radio. We developed a new method based on the Akaike information criterion to identify double bump showers in simulations by analyzing their longitudinal profiles. Then we investigate the prevalence of these double bump showers across different cosmic ray primary particles and various hadronic interaction models. We create a skeleton of the EAS which consists of all the particles with at least $1\%$ of the primary energy, allowing us to confirm the leading particle hypothesis and track shower development following these particles. This will enable us to relate the attributes of the leading particle to measurable parameters. Depending on the exact shower properties, the radio footprint of a double bump shower can create a complex interference pattern, consisting of multiple rings. From this information, the longitudinal profiles can be extracted. SKA due to its dense antenna array and frequency range will be the first experiment able to observe these double bump showers in detail.

astro-ph.HE↗

arXiv2025

A novel approach for air shower profile reconstruction with dense radio antenna arrays using Information Field Theory

Reconstructing the longitudinal profile of extensive air showers, generated from the interaction of cosmic rays in the Earth's atmosphere, is crucial to understanding their mass composition, which in turn provides valuable insight on their possible sources of origin. Dense radio antenna arrays such as the LOw Frequency ARray (LOFAR) telescope as well as the upcoming Square Kilometre Array Observatory (SKAO) are ideal instruments to explore the potential of air shower profile reconstruction, as their high antenna density allows cosmic ray observations with unprecedented accuracy. However, current analysis approaches can only recover $X_\mathrm{max}$, the atmospheric depth at shower maximum, and heavily rely on computationally expensive simulations. As such, it is ever more crucial to develop new analysis approaches that can perform a full air shower profile reconstruction efficiently. In this work, we develop a novel framework to reconstruct the longitudinal profile of air showers using measurements from radio detectors with Information Field Theory (IFT), a state-of-the-art reconstruction framework based on Bayesian inference. Through IFT, we are able to exploit all available information in the signal (amplitude, phase, and pulse shape) at each antenna position simultaneously and explicitly utilise models that are motivated through our current understanding of air shower physics. We verify our framework on simulated datasets prepared for LOFAR, showcasing that we can not only reconstruct the air shower profile with uncertainties in each atmospheric depth bin but also recover the reconstructed trace at each antenna position. Our framework demonstrates that radio measurements with dense antenna layouts such as LOFAR and SKAO have the capability to go beyond reconstruction of $X_\mathrm{max}$ and will thus aid in our understanding of the mass composition of cosmic rays.

astro-ph.IM↗

arXiv2025

Radio emission from airplanes as observed with RNO-G

This paper describes how intentional and unintentional radio emission from airplanes is recorded with the Radio Neutrino Observatory Greenland (RNO-G). We characterize the received signals and define a procedure to extract a clean set of impulsive signals. These signals are highly suitable for instrument calibration, also for future experiments. A set of signals is used to probe the timing precision of RNO-G in-situ, which is found to match expectations. We also discuss the impact of these signals on the ability to detect neutrinos with RNO-G.

hep-ex↗

arXiv2025

A LOFAR-style reconstruction of cosmic-ray air showers with SKA-Low

Cosmic-ray air shower detection with the low-frequency part of the Square Kilometre Array (SKA) radio telescope is envisioned to yield very high precision measurements of the particle composition of cosmic rays between $10^{16}$ and $10^{18}$ eV. This is made possible by the extreme antenna density of the core of SKA-Low, surpassing the current most dense radio air shower observatory LOFAR by over an order of magnitude. In order to make these measurements, the technical implementation of this observation mode and the development of reconstruction methods have to happen hand-in-hand. As a first lower limit of what is obtainable, we apply the current most precise reconstruction methods as used at LOFAR to a first complete simulation of air shower signals for the SKA-Low array. We describe this simulation setup and discuss the obtainable accuracy and resolution. A special focus is put on effects of the dynamic range of the system, beamforming methods to lower the energy threshold, as well as the limits to the mass composition accuracy given by statistical and systematic uncertainties.

astro-ph.HE↗

arXiv2025

Probing the Firn Refractive Index Profile Using Antenna Response

The Radio Neutrino Observatory-Greenland (RNO-G, at Summit Station) experiment comprises an extensive fat-dipole antenna array deployed into ice boreholes over an eventual area of approximately 35 ${\rm km}^2$. Since the RNO-G experimental sensitivity depends on the radio-frequency properties of the firn, which are known to vary laterally on sub-km distance scales and vertically on sub-meter distance scales, a technique for quickly extracting information on firn ice properties with depth ($n(z)$) during drilling and deployment is desirable. Given that a dipole's resonant wavelength is fixed by geometry, the resonant frequency $f_{res}$ (measured as an S-parameter reflection coefficient [`$S_{11}$'] minimum) scales inversely with the local refractive index, allowing a translation of a depth-dependent $S_{11}$(z) profile into $n(z)$. $S_{11}$(z) data were initially taken in August, 2024 using a dipole lowered into a newly-drilled $98\pm 1$-mm diameter, 350-m deep borehole at Summit Station, Greenland, approximately 1 km from the site of the original GISP-2 core; improved measurements were subsequently made in May, 2025. We conclude that $S_{11}$(z) data can be used to estimate \RIP, on 50 cm vertical scales, at the per-cent level of accuracy required by experiments such as RN0-G.

astro-ph.IM↗

arXiv2024

Instrument design and performance of the first seven stations of RNO-G

The Radio Neutrino Observatory in Greenland (RNO-G) is the first in-ice radio array in the northern hemisphere for the detection of ultra-high energy neutrinos via the coherent radio emission from neutrino-induced particle cascades within the ice. The array is currently in phased construction near Summit Station on the Greenland ice sheet, with 7~stations deployed during the first two boreal summer field seasons of 2021 and 2022. In this paper, we describe the installation and system design of these initial RNO-G stations, and discuss the performance of the array as of summer 2024.

astro-ph.IM↗

arXiv2024

Aperture correction for Beamforming in radiometric detection of ultra-high energy cosmic rays

For high-energy cosmic-ray physics, it is imperative to determine the mass and energy of the cosmic ray that initiated the air shower in the atmosphere. This information can be extracted from the longitudinal profile of the air shower. In radio-metric observations, this profile is customarily determined through an extensive fitting procedure where calculated radio intensity is fitted to data. Beamforming the measured signals offers a promising alternative to bypass the cumbersome fitting procedure and to determine the longitudinal profile directly. Finite aperture effects in beamforming hamper the resolution with which this profile can be determined. We present a comprehensive investigation of the beamforming resolution in radiometric observations of air showers. There are two, principally different, approaches possible in air-shower beamforming, one where the total beamforming intensity is determined and an alternative where the beamforming trace is cross-correlated with a known response function. The effects due to a finite aperture (size of antenna array and bandwidth) are large for both approaches. We argue that it is possible to correct for the aperture corrections using an unfolding procedure. We give an explicit expression for the folding function, the kernel. Being able to calculate the folding function allows for unfolding the finite aperture effects from the data. We show that, in a model-to-model comparison, this allows for an accurate reconstruction of the current profile as the shower develops in the atmosphere. We present also an example where we reconstruct the longitudinal current profile of a shower developing under thunderstorm conditions where the atmospheric electric fields greatly alter the orientation of the transverse current in the shower front.

astro-ph.IM↗

arXiv2024

Cosmic ray detection with the LOFAR radio telescope

The LOw Frequency ARray (LOFAR) has successfully measured cosmic rays for over a decade now. With its dense core of antenna fields in the Netherlands, it is an ideal tool for studying the radio emission from extensive air showers in the $10^{16}$ eV to $10^{18.5}$ eV range. Every air shower is measured with a small particle detector array and hundreds of antennas, which sets LOFAR apart from other air shower arrays. We present our current achievements and progress in reconstruction, interpolation, and software development during the final phases of measurement of LOFAR 1.0, before the LOFAR array gets a significant upgrade, including also plans for the final data release and refined analyses.

astro-ph.HE↗

arXiv2024

Solar flare observations with the Radio Neutrino Observatory Greenland (RNO-G)

The Radio Neutrino Observatory - Greenland (RNO-G) seeks discovery of ultra-high energy neutrinos from the cosmos through their interactions in ice. The science program extends beyond particle astrophysics to include radioglaciology and, as we show herein, solar observations, as well. Currently seven of 35 planned radio-receiver stations (24 antennas/station) are operational. These stations are sensitive to impulsive radio signals with frequencies between 80 and 700 MHz and feature a neutrino trigger threshold for recording data close to the thermal floor. RNO-G can also trigger on elevated signals from the Sun, resulting in nanosecond resolution time-domain flare data; such temporal resolution is significantly shorter than from most dedicated solar observatories. In addition to possible RNO-G solar flare polarization measurements, the Sun also represents an extremely useful above-surface calibration source. Using RNO-G data recorded during the summers of 2022 and 2023, we find signal excesses during solar flares reported by the solar-observing Callisto network and also in coincidence with $\sim$2/3 of the brightest excesses recorded by the SWAVES satellite. These observed flares are characterized by significant time-domain impulsivity. Using the known position of the Sun, the flare sample is used to calibrate the RNO-G absolute pointing on the radio signal arrival direction to sub-degree resolution. We thus establish the Sun as a regularly observed astronomical calibration source to provide the accurate absolute pointing required for neutrino astronomy.

astro-ph.SR↗

arXiv2023

Developing New Analysis Tools for Near Surface Radio-based Neutrino Detectors

The ARIANNA experiment is an Askaryan radio detector designed to measure high-energy neutrino induced cascades within the Antarctic ice. Ultra-high-energy neutrinos above $10^{16}$ eV have an extremely low flux, so experimental data captured at trigger level need to be classified correctly to retain more neutrino signal. We first describe two new physics-based neutrino selection methods, (the updown and dipole cut) that extend the previously published analysis to a specialized ARIANNA station with 8 antenna channels, which is double the number used in the prior analysis. For a standard trigger with a threshold signal to noise ratio at 4.4, the new cuts produce a neutrino efficiency of > 95% per station-year, while rejecting 99.93% of the background (corresponding to 53 remaining experimental background events). When the new cuts are combined with a previously developed cut using neutrino waveform templates, all background is removed at no change of efficiency. In addition, the neutrino efficiency is extrapolated to 1,000 station-years, obtaining 91%. This work then introduces a new selection method (deep learning (DL) cut) to augment the identification of neutrino events by using DL methods and compares the efficiency to the physics-based analysis. The DL cut gives 99% signal efficiency per station-year of operation while rejecting 99.997% of the background (corresponding to 2 remaining experimental background events), which are then removed by the waveform template cut at no significant change in efficiency. The results of the DL cut were verified using measured cosmic rays which shows the simulations do not introduce artifacts with respect to experimental data. The paper demonstrates the background rejection and signal efficiency of near surface antennas meets the requirements of a large scale future array, as considered in baseline design of the radio component of IceCube-Gen2.

astro-ph.HE↗

arXiv2023

A high-precision interpolation method for pulsed radio signals from cosmic-ray air showers

Analysis of radio signals from cosmic-ray induced air showers has been shown to be a reliable method to extract shower parameters such as primary energy and depth of shower maximum. The required detailed air shower simulations take 1 to 3 days of CPU time per shower for a few hundred antennas. With nearly $60,000$ antennas envisioned to be used for air shower studies at the Square Kilometre Array (SKA), simulating all of these would come at unreasonable costs. We present an interpolation algorithm to reconstruct the full pulse time series at any position in the radio footprint, from a set of antennas simulated on a polar grid. Relying on Fourier series representations and cubic splines, it significantly improves on existing linear methods. We show that simulating about 200 antennas is sufficient for high-precision analysis in the SKA era, including e.g. interferometry which relies on accurate pulse shapes and timings. We therefore propose the interpolation algorithm and its implementation as a useful extension of radio simulation codes, to limit computational effort while retaining accuracy.

astro-ph.IM↗

arXiv2023

Reconstructing Air Shower Parameters with MGMR3D

Measuring the radio emission from cosmic ray particle cascades has proven to be a very efficient method to determine their properties such as the mass composition. Efficient modeling of the radio emission from air showers is crucial in order to extract the cosmic ray physics parameters from the measured radio emission. MGMR3D is a fast semi-analytic code that calculates the complete radio footprint, i.e.\ intensity, polarization, and pulse shapes, for a parametrized shower-current density and can be used in a chi-square optimization to fit a given radio data. It is many orders of magnitude faster than its Monte Carlo counterparts. We provide a detailed comparative study of MGMR3D to Monte Carlo simulations, where, with improved parametrizations, the shower maximum $\Xmax$ is found to have very strong agreement with a small dependency on the incoming zenith angle of the shower. Another interesting feature we observe with MGMR3D is sensitivity to the shape of the longitudinal profile in addition to $\Xmax$. This is achieved by probing the distinguishable radio footprint produced by a shower having a different longitudinal profile than usual. Furthermore, for the first time, we show the results of reconstructing shower parameters for LOFAR data using MGMR3D, and obtaining a $\Xmax$ resolution of 22 g/cm$^2$ and energy resolution of 19\%.

astro-ph.HE↗

arXiv2023

Constraining the cosmic-ray mass composition by measuring the shower length with SKA

The current generation of air shower radio arrays has demonstrated that the atmospheric depth of the shower maximum Xmax can be reconstructed with high accuracy. These experiments are now contributing to mass composition studies in the energy range where a transition from galactic to extragalactic cosmic-ray sources is expected. However, we are still far away from an unambiguous interpretation of the data. Here we propose to use radio measurements to derive a new type of constraint on the mass composition, by reconstructing the shower length L. The low-frequency part of the Square Kilometer Array will have an extremely high antenna density of roughly 60.000 antennas within one square kilometer, and is the perfect site for high-resolution studies of air showers. In this contribution, we discuss the impact of being able to reconstruct L, and the unique contribution that SKA can make to cosmic-ray science.

astro-ph.HE↗

arXiv2023

Precision measurement of the index of refraction of deep glacial ice at radio frequencies at Summit Station, Greenland

Glacial ice is used as a target material for the detection of ultra-high energy neutrinos, by measuring the radio signals that are emitted when those neutrinos interact in the ice. Thanks to the large attenuation length at radio frequencies, these signals can be detected over distances of several kilometers. One experiment taking advantage of this is the Radio Neutrino Observatory Greenland (RNO-G), currently under construction at Summit Station, near the apex of the Greenland ice sheet. These experiments require a thorough understanding of the dielectric properties of ice at radio frequencies. Towards this goal, calibration campaigns have been undertaken at Summit, during which we recorded radio reflections off internal layers in the ice sheet. Using data from the nearby GISP2 and GRIP ice cores, we show that these reflectors can be associated with features in the ice conductivity profiles; we use this connection to determine the index of refraction of the bulk ice as n=1.778 +/- 0.006.

astro-ph.IM↗

arXiv2023

Prospects for measuring the longitudinal particle distribution of cosmic-ray air showers with SKA

We explore the possibilities of measuring the longitudinal profile of individual air showers beyond $X_{\rm max}$ when using very dense radio arrays such as SKA. The low-frequency part of the Square Kilometre Array, to be built in Australia, features an enormous antenna density of about $50,000$ antennas in the inner core region of radius 500 m, with a frequency band from 50 to 350 MHz. From CoREAS simulations, a SKA-Low antenna model plus noise contributions, and adapted LOFAR analysis scripts, we obtain a resolution in the shower maximum $X_{\rm max}$ and energy that is considerably better than at LOFAR. Already from this setup, we show that at least one additional parameter of the longitudinal profile can be measured. This would improve mass composition analysis by measuring an additional composition-dependent quantity. Moreover, it would offer an opportunity to discriminate between the different predictions of hadronic interaction models, hence contributing to hadronic physics at energy levels beyond man-made accelerators.

astro-ph.HE↗