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 × 1017 eV. We use an astrophysical model with two extragalactic source populations to model the hardening of the cosmic-ray flux at around 5 × 1018 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)

DELLA-Induced Early Transcriptional Changes during Etiolated Development in Arabidopsis thaliana

The hormones gibberellins (GAs) control a wide variety of processes in plants, including stress and developmental responses. This task largely relies on the activity of the DELLA proteins, nuclear-localized transcriptional regulators that do not seem to have DNA binding capacity. The identification of early target genes of DELLA action is key not only to understand how GAs regulate physiological responses, but also to get clues about the molecular mechanisms by which DELLAs regulate gene expression. Here, we have investigated the global, early transcriptional response triggered by the Arabidopsis DELLA protein GAI during skotomorphogenesis, a developmental program tightly regulated by GAs. Our results show that the induction of GAI activity has an almost immediate effect on gene expression. Although this transcriptional regulation is largely mediated by the PIFs and HY5 transcription factors based on target meta-analysis, additional evidence points to other transcription factors that would be directly involved in DELLA regulation of gene expression. First, we have identified cis elements recognized by Dofs and type-B ARRs among the sequences enriched in the promoters of GAI targets; and second, an enrichment in additional cis elements appeared when this analysis was extended to a dataset of early targets of the DELLA protein RGA: CArG boxes, bound by MADS-box proteins, and the E-box CACATG that links the activity of DELLAs to circadian transcriptional regulation. Finally, Gene Ontology analysis highlights the impact of DELLA regulation upon the homeostasis of the GA, auxin, and ethylene pathways, as well as upon pre-existing transcriptional networks

Radio measurements of the depth of air-shower maximum at the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA), part of the Pierre Auger Observatory, is currently the largest array of radio antenna stations deployed for the detection of cosmic rays, spanning an area of 17 km2 with 153 radio stations. It detects the radio emission of extensive air showers produced by cosmic rays in the 30-80 MHz band. Here, we report the AERA measurements of the depth of the shower maximum (Xmax), a probe for mass composition, at cosmic-ray energies between 1017.5 and 1018.8 eV, which show agreement with earlier measurements with the fluorescence technique at the Pierre Auger Observatory. We show advancements in the method for radio Xmax reconstruction by comparison to dedicated sets of corsika/coreas air-shower simulations, including steps of reconstruction-bias identification and correction, which is of particular importance for irregular or sparse radio arrays. Using the largest set of radio air-shower measurements to date, we show the radio Xmax resolution as a function of energy, reaching a resolution better than 15 g cm-2 at the highest energies, demonstrating that radio Xmax measurements are competitive with the established high-precision fluorescence technique. In addition, we developed a procedure for performing an extensive data-driven study of systematic uncertainties, including the effects of acceptance bias, reconstruction bias, and the investigation of possible residual biases. These results have been cross-checked with air showers measured independently with both the radio and fluorescence techniques, a setup unique to the Pierre Auger Observatory

A Search for Photons with Energies Above 2 x 1017 eV Using Hybrid Data from the Low-Energy Extensions of the Pierre Auger Observatory

Ultra-high-energy photons with energies exceeding 10¹⁷ eV offer a wealth of connections to different aspects of cosmic-ray astrophysics as well as to gamma-ray and neutrino astronomy. The recent observations of photons with energies in the 10¹⁵ eV range further motivate searches for even higher-energy photons. In this paper, we present a search for photons with energies exceeding 2 × 10¹⁷ eV using about 5.5 yr of hybrid data from the low-energy extensions of the Pierre Auger Observatory. The upper limits on the integral photon flux derived here are the most stringent ones to date in the energy region between 10¹⁷ and 10¹⁸ eV.P. Abreu ... J. M. Albury ... J. A. Bellido ... R. W. Clay ... B. R. Dawson, J. A. Day ... T. D. Grubb ... V. M. Harvey ... G. C. Hill ... B. C. Manning ... T. Sudholz ... et al. (The Pierre Auger Collaboration

Scaler Rates from the Pierre Auger Observatory: A New Proxy of Solar Activity

The modulation of low-energy galactic cosmic rays reflects interplanetary magnetic field variations and can provide useful information on solar activity. An array of ground-surface detectors can reveal the secondary particles, which originate from the interaction of cosmic rays with the atmosphere. In this work, we present an investigation of the low-threshold rate (scaler) time series recorded in 16 yr of operation by the Pierre Auger Observatory surface detectors in Malargüe, Argentina. Through an advanced spectral analysis, we detected highly statistically significant variations in the time series with periods ranging from the decadal to the daily scale. We investigate their origin, revealing a direct connection with solar variability. Thanks to their intrinsic very low noise level, the Auger scalers allow a thorough and detailed investigation of the galactic cosmic-ray flux variations in the heliosphere at different timescales and can, therefore, be considered a new proxy of solar variability

Improving the photon sensitivity of the Pierre Auger Observatory with the AugerPrime Radio Detector

The AugerPrime upgrade represents a significant enhancement in the capability of the Pierre Auger Observatory to detect air showers. Central to this advancement is the installation of a radio antenna atop each existing Surface Detector station, constituting the Radio Detector (RD). The RD enhances the sensitivity of the Surface Detector to the electromagnetic component of air showers. Hence, the new detector presents an opportunity for the discovery of rare particles such as ultra-high-energy photons. This contribution shows the development efforts towards an RD trigger with focus on the detection of rare particles. The radio trigger designed for the detection of photon-induced events will be outlined, and the challenge of a radio background consisting of human-made noise is discussed. The trigger efficiency and reconstruction accuracy are studied with simulations. The presentation will conclude by summarizing the effectiveness of the new detector component

Drone-based calibration of AugerPrime radio antennas at the Pierre Auger Observatory

Radio emissions of extensive air showers can be observed at the Pierre Auger Observatory with the AugerPrime Radio Detector (RD). As part of the AugerPrime upgrade, RD is being installed on 1660 water-Cherenkov detectors on an area of about 3000 km2 and consists of dual-polarized Short Aperiodic Loaded Loop Antennas (SALLA). To achieve high measurement precision, RD needs to be well-calibrated, which requires the antenna response pattern to be well-known. We introduce a method to measure the directional response of the SALLA using a well-defined biconical antenna mounted to a drone. The drone-based setup possesses active stabilization and precise pointing with the use of a gimbal. Additionally, the drone’s position is tracked using differential GPS with O(cm) precision. This setup allows us to precisely extract the antenna response pattern from any direction in the frequency range of 30 − 80 MHz. In a recent in-situ campaign, calibration measurements of the AugerPrime radio detector have been performed. First results of these measurements are presented and compared to simulations