arXiv subjects

S. Buitink

Publications and source records attributed to S. Buitink.

At least 55 records · Page 3Linked to original sources

arXiv2024

Testing Hadronic-Model Predictions of Depth of Maximum of Air-Shower Profiles and Ground-Particle Signals using Hybrid Data of the Pierre Auger Observatory

We test the predictions of hadronic interaction models regarding the depth of maximum of air-shower profiles, $X_{max}$, and ground-particle signals in water-Cherenkov detectors at 1000 m from the shower core, $S(1000)$, using the data from the fluorescence and surface detectors of the Pierre Auger Observatory. The test consists in fitting the measured two-dimensional ($S(1000)$, $X_{max}$) distributions using templates for simulated air showers produced with hadronic interaction models EPOS-LHC, QGSJet II-04, Sibyll 2.3d and leaving the scales of predicted $X_{max}$ and the signals from hadronic component at ground as free fit parameters. The method relies on the assumption that the mass composition remains the same at all zenith angles, while the longitudinal shower development and attenuation of ground signal depend on the mass composition in a correlated way. The analysis was applied to 2239 events detected by both the fluorescence and surface detectors of the Pierre Auger Observatory with energies between $10^{18.5}$ to $10^{19.0}$ eV and zenith angles below $60^\circ$. We found, that within the assumptions of the method, the best description of the data is achieved if the predictions of the hadronic interaction models are shifted to deeper $X_{max}$ values and larger hadronic signals at all zenith angles. Given the magnitude of the shifts and the data sample size, the statistical significance of the improvement of data description using the modifications considered in the paper is larger than $5σ$ even for any linear combination of experimental systematic uncertainties.

astro-ph.HE↗

arXiv2024

Constraints on metastable superheavy dark matter coupled to sterile neutrinos with the Pierre Auger Observatory

Dark matter particles could be superheavy, provided their lifetime is much longer than the age of the universe. Using the sensitivity of the Pierre Auger Observatory to ultra-high energy neutrinos and photons, we constrain a specific extension of the Standard Model of particle physics that meets the lifetime requirement for a superheavy particle by coupling it to a sector of ultra-light sterile neutrinos. Our results show that, for a typical dark coupling constant of 0.1, the mixing angle $θ_m$ between active and sterile neutrinos must satisfy, roughly, $θ_m \lesssim 1.5\times 10^{-6}(M_X/10^9~\mathrm{GeV})^{-2}$ for a mass $M_X$ of the dark-matter particle between $10^8$ and $10^{11}~$GeV.

hep-ph↗

arXiv2024

Constraining models for the origin of ultra-high-energy cosmic rays with a novel combined analysis of arrival directions, spectrum, and composition data measured at the Pierre Auger Observatory

The combined fit of the measured energy spectrum and shower maximum depth distributions of ultra-high-energy cosmic rays is known to constrain the parameters of astrophysical models with homogeneous source distributions. Studies of the distribution of the cosmic-ray arrival directions show a better agreement with models in which a fraction of the flux is non-isotropic and associated with the nearby radio galaxy Centaurus A or with catalogs such as that of starburst galaxies. Here, we present a novel combination of both analyses by a simultaneous fit of arrival directions, energy spectrum, and composition data measured at the Pierre Auger Observatory. We find that a model containing a flux contribution from the starburst galaxy catalog of around 20% at 40 EeV with a magnetic field blurring of around $20^\circ$ for a rigidity of 10 EV provides a fair simultaneous description of all three observables. The starburst galaxy model is favored with a significance of $4.5σ$ (considering experimental systematic effects) compared to a reference model with only homogeneously distributed background sources. By investigating a scenario with Centaurus A as a single source in combination with the homogeneous background, we confirm that this region of the sky provides the dominant contribution to the observed anisotropy signal. Models containing a catalog of jetted active galactic nuclei whose flux scales with the $γ$-ray emission are, however, disfavored as they cannot adequately describe the measured arrival directions.

astro-ph.HE↗

arXiv2023

Ground observations of a space laser for the assessment of its in-orbit performance

The wind mission Aeolus of the European Space Agency was a groundbreaking achievement for Earth observation. Between 2018 and 2023, the space-borne lidar instrument ALADIN onboard the Aeolus satellite measured atmospheric wind profiles with global coverage which contributed to improving the accuracy of numerical weather prediction. The precision of the wind observations, however, declined over the course of the mission due to a progressive loss of the atmospheric backscatter signal. The analysis of the root cause was supported by the Pierre Auger Observatory in Argentina whose fluorescence detector registered the ultraviolet laser pulses emitted from the instrument in space, thereby offering an estimation of the laser energy at the exit of the instrument for several days in 2019, 2020 and 2021. The reconstruction of the laser beam not only allowed for an independent assessment of the Aeolus performance, but also helped to improve the accuracy in the determination of the laser beam's ground track on single pulse level. The results presented in this paper set a precedent for the monitoring of space lasers by ground-based telescopes and open new possibilities for the calibration of cosmic-ray observatories.

astro-ph.IM↗

arXiv2023

AugerPrime Surface Detector Electronics

Operating since 2004, the Pierre Auger Observatory has led to major advances in our understanding of the ultra-high-energy cosmic rays. The latest findings have revealed new insights that led to the upgrade of the Observatory, with the primary goal of obtaining information on the primary mass of the most energetic cosmic rays on a shower-by-shower basis. In the framework of the upgrade, called AugerPrime, the 1660 water-Cherenkov detectors of the surface array are equipped with plastic scintillators and radio antennas, allowing us to enhance the composition sensitivity. To accommodate new detectors and to increase experimental capabilities, the electronics is also upgraded. This includes better timing with up-to-date GPS receivers, higher sampling frequency, increased dynamic range, and more powerful local processing of the data. In this paper, the design characteristics of the new electronics and the enhanced dynamic range will be described. The manufacturing and test processes will be outlined and the test results will be discussed. The calibration of the SD detector and various performance parameters obtained from the analysis of the first commissioning data will also be presented.

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

Search for UHE Photons from Gravitational Wave Sources with the Pierre Auger Observatory

A search for time-directional coincidences of ultra-high-energy (UHE) photons above 10 EeV with gravitational wave (GW) events from the LIGO/Virgo runs O1 to O3 is conducted with the Pierre Auger Observatory. Due to the distinctive properties of photon interactions and to the background expected from hadronic showers, a subset of the most interesting GW events is selected based on their localization quality and distance. Time periods of 1000 s around and 1 day after the GW events are analyzed. No coincidences are observed. Upper limits on the UHE photon fluence from a GW event are derived that are typically at $\sim$7 MeV cm$^{-2}$ (time period 1000~s) and $\sim$35 MeV cm$^{-2}$ (time period 1 day). Due to the proximity of the binary neutron star merger GW170817, the energy of the source transferred into UHE photons above 40 EeV is constrained to be less than 20% of its total gravitational wave energy. These are the first limits on UHE photons from GW sources.

astro-ph.HE↗

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

Constraining the sources of ultra-high-energy cosmic rays across and above the ankle with the spectrum and composition data measured at the Pierre Auger Observatory

In this work we present the interpretation of the energy spectrum and mass composition data as measured by the Pierre Auger Collaboration above $6 \times 10^{17}$ eV. We use an astrophysical model with two extragalactic source populations to model the hardening of the cosmic-ray flux at around $5\times 10^{18}$ eV (the so-called "ankle" feature) as a transition between these two components. We find our data to be well reproduced if sources above the ankle emit a mixed composition with a hard spectrum and a low rigidity cutoff. The component below the ankle is required to have a very soft spectrum and a mix of protons and intermediate-mass nuclei. The origin of this intermediate-mass component is not well constrained and it could originate from either Galactic or extragalactic sources. To the aim of evaluating our capability to constrain astrophysical models, we discuss the impact on the fit results of the main experimental systematic uncertainties and of the assumptions about quantities affecting the air shower development as well as the propagation and redshift distribution of injected ultra-high-energy cosmic rays (UHECRs).

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

Search for photons above 10$^{19}$ eV with the surface detector of the Pierre Auger Observatory

We use the surface detector of the Pierre Auger Observatory to search for air showers initiated by photons with an energy above $10^{19}$ eV. Photons in the zenith angle range from 30$^\circ$ to 60$^\circ$ can be identified in the overwhelming background of showers initiated by charged cosmic rays through the broader time structure of the signals induced in the water-Cherenkov detectors of the array and the steeper lateral distribution of shower particles reaching ground. Applying the search method to data collected between January 2004 and June 2020, upper limits at 95\% CL are set to an $E^{-2}$ diffuse flux of ultra-high energy photons above $10^{19}$ eV, $2{\times}10^{19}$ eV and $4{\times}10^{19}$ eV amounting to $2.11{\times}10^{-3}$, $3.12{\times}10^{-4}$ and $1.72{\times}10^{-4}$ km$^{-2}$ sr$^{-1}$ yr$^{-1}$, respectively. While the sensitivity of the present search around $2 \times 10^{19}$ eV approaches expectations of cosmogenic photon fluxes in the case of a pure-proton composition, it is one order of magnitude above those from more realistic mixed-composition models. The inferred limits have also implications for the search of super-heavy dark matter that are discussed and illustrated.

astro-ph.HE↗

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↗

arXiv2022

Cosmological implications of photon-flux upper limits at ultra-high energies in scenarios of Planckian-interacting massive particles for dark matter

Using the data of the Pierre Auger Observatory, we report on a search for signatures that would be suggestive of super-heavy particles decaying in the Galactic halo. From the lack of signal, we present upper limits for different energy thresholds above ${\gtrsim}10^8$\,GeV on the secondary by-product fluxes expected from the decay of the particles. Assuming that the energy density of these super-heavy particles matches that of dark matter observed today, we translate the upper bounds on the particle fluxes into tight constraints on the couplings governing the decay process as a function of the particle mass. Instantons, which are non-perturbative solutions to Yang-Mills equations, can give rise to decay channels otherwise forbidden and transform stable particles into meta-stable ones. Assuming such instanton-induced decay processes, we derive a bound on the reduced coupling constant of gauge interactions in the dark sector: $α_X \lesssim 0.09$, for $10^{9} \lesssim M_X/\text{GeV} < 10^{19}$. Conversely, we obtain that, for instance, a reduced coupling constant $α_X = 0.09$ excludes masses $M_X \gtrsim 3\times 10^{13}~$GeV. In the context of dark matter production from gravitational interactions alone during the reheating epoch, we derive constraints on the parameter space that involves, in addition to $M_X$ and $α_X$, the Hubble rate at the end of inflation, the reheating efficiency, and the non-minimal coupling of the Higgs with curvature.

astro-ph.HE↗

arXiv2022

Limits to gauge coupling in the dark sector set by the non-observation of instanton-induced decay of Super-Heavy Dark Matter in the Pierre Auger Observatory data

Instantons, which are non-perturbative solutions to Yang-Mills equations, provide a signal for the occurrence of quantum tunneling between distinct classes of vacua. They can give rise to decays of particles otherwise forbidden. Using data collected at the Pierre Auger Observatory, we search for signatures of such instanton-induced processes that would be suggestive of super-heavy particles decaying in the Galactic halo. These particles could have been produced during the post-inflationary epoch and match the relic abundance of dark matter inferred today. The non-observation of the signatures searched for allows us to derive a bound on the reduced coupling constant of gauge interactions in the dark sector: $α_X \lesssim 0.09$, for $10^{9} \lesssim M_X/{\rm GeV} < 10^{19}$. Conversely, we obtain that, for instance, a reduced coupling constant $α_X = 0.09$ excludes masses $M_X \gtrsim 3\times 10^{13}~$GeV. In the context of dark matter production from gravitational interactions alone, we illustrate how these bounds are complementary to those obtained on the Hubble rate at the end of inflation from the non-observation of tensor modes in the cosmological microwave background.

astro-ph.HE↗

arXiv2022

Radiofrequency Ice Dielectric Measurements at Summit Station, Greenland

We recently reported on the radio-frequency attenuation length of cold polar ice at Summit Station, Greenland, based on bistatic radar measurements of radio-frequency bedrock echo strengths taken during the summer of 2021. Those data also include echoes attributed to stratified impurities or dielectric discontinuities within the ice sheet (layers), which allow studies of a) estimation of the relative contribution of coherent (discrete layers, e.g.) vs. incoherent (bulk volumetric, e.g.) scattering, b) the magnitude of internal layer reflection coefficients, c) limits on the azimuthal asymmetry of reflections (birefringence), and d) limits on signal dispersion in-ice over a bandwidth of ~100 MHz. We find that i) after averaging 10000 echo triggers, reflected signal observable over the thermal floor (to depths of approximately 1500 m) are consistent with being entirely coherent, ii) internal layer reflection coefficients are measured at approximately -60 to -70 dB, iii) birefringent effects for vertically propagating signals are smaller by an order of magnitude relative to comparable studies performed at South Pole, and iv) within our experimental limits, glacial ice is non-dispersive over the frequency band relevant for neutrino detection experiments.

physics.ins-det↗

arXiv2022

A Catalog of the Highest-Energy Cosmic Rays Recorded During Phase I of Operation of the Pierre Auger Observatory

A catalog containing details of the highest-energy cosmic rays recorded through the detection of extensive air-showers at the Pierre Auger Observatory is presented with the aim of opening the data to detailed examination. Descriptions of the 100 showers created by the highest-energy particles recorded between 1 January 2004 and 31 December 2020 are given for cosmic rays that have energies in the range 78 EeV to 166 EeV. Details are also given of a further nine very-energetic events that have been used in the calibration procedure adopted to determine the energy of each primary. A sky plot of the arrival directions of the most energetic particles is shown. No interpretations of the data are offered.

astro-ph.HE↗

arXiv2022

Searches for Ultra-High-Energy Photons at the Pierre Auger Observatory

The Pierre Auger Observatory, being the largest air-shower experiment in the world, offers an unprecedented exposure to neutral particles at the highest energies. Since the start of data taking more than 18 years ago, various searches for ultra-high-energy (UHE, $E\gtrsim10^{17}\,\text{eV}$) photons have been performed: either for a diffuse flux of UHE photons, for point sources of UHE photons or for UHE photons associated with transient events like gravitational wave events. In the present paper, we summarize these searches and review the current results obtained using the wealth of data collected by the Pierre Auger Observatory.

astro-ph.HE↗