In its Phase I, the Pierre Auger Observatory has led to several observations, driving the field of ultra-high-energy cosmic ray (UHECR) research over the last 20 years. Major achievements obtained so far include the unprecedented precise energy spectrum and its features, the observables linked to the UHECR mass composition and the distribution of arrival directions of the most energetic...
Assuming an extreme scenario, in which the arriving cosmic rays are composed of only iron nuclei at energies above 10$^{19.6}$ eV, and preserving the elongation rate predicted by models of hadronic interactions, we derive the shift of the scale of the depth of shower maximum (Xmax) predicted by these models using the public data from the Pierre Auger Observatory. We then propose a new...
The origin of ultra-high-energy cosmic rays (UHECRs) remains a major open question in astrophysics. Observational data suggest that starburst galaxies and active galactic nuclei (AGNs) are the most promising sources. However, accelerating particles to energies above 1 EeV in these environments is complex due to the demanding requirements on energy, density, and metallicity imposed by...
Though the maximum energy of the charged cosmic ray observations exceeds 100EeV, the energy frontier of the gamma-ray observations is PeV. In the past years, Tibet ASgamma, HAWC and LHAASO opened a new window of astronomy in the sub-PeV to PeV range, which is important to unveil yet unknown PeV cosmic accelerators in our galaxy. As they are all located in the northern hemisphere, observations...
The origin of Ultra-High-Energy Cosmic Rays (UHECRs) is one of the biggest mysteries in modern astrophysics.
Since UHECRs are deflected by Galactic and Extra-Galactic magnetic fields, their arrival directions do not point to their sources. Previous analyses conducted on the arrival directions of high energy events ($E>32\,\text{EeV}$) recorded by the Surface Detector of the Pierre Auger...
The TA×4 experiment, which has been ongoing since a portion of the detectors were newly installed in 2019, aims to reveal the origin of UHECRs by expanding the detection area of the TA experiment by a factor of four and increasing the number of observed events. In the analysis with the surface detector (SD) of the TA×4 experiment, the reconstruction method has already been established for...
The field of ultra-high-energy cosmic ray (UHECR) astronomy has been facing an ongoing challenge due to the unknown impact of magnetic deflections on the observed events. However, with the recent successes in employing deep neural networks (DNN) to reconstruct data from multiple types of surface detectors, the wider availability of mass-sensitive datasets is expected to arrive within the next...
Star-forming environments such as star-forming and Starburst Galaxies (SFGs and SBGs) experience intense phases of stellar formation activity. The Fermi-LAT collaboration has found a correlation between the gamma-ray and infrared luminosities for a sample of local SFGs and SBGs. Yet, the nature of CR transport inside these sources is still under debate. In this talk, I will discuss novel and...
The arrival directions of cosmic rays are significantly influenced by the Galactic and and extragalactic magnetic fields, especially for a heavy mass-composition of the primary particles. Following recent studies, we assume a heavy mass-composition of primary particles at the highest energies, pure iron nuclei above $10^{19.6}$ eV, and explore the arrival directions of such particles using the...
With the knowledge and statistical power derived from two decades of measurements, the Pierre Auger Observatory has significantly advanced our understanding of ultra-high-energy cosmic rays whilst unearthing an increasingly complex astrophysical scenario and tensions with hadronic interaction models. The field now demands primary mass as an observable with an exposure that only the surface...
We use the reconstructed properties of the Amaterasu particle, the second-highest energy cosmic ray ever detected, to map out three-dimensional constraints on the location of its unknown source. We highlight possible astrophysical sources that are compatible with these regions and requirements. Among these, M82, a powerful starburst galaxy, stands out as a strong candidate due to its position...
Accurate calibration of the Telescope Array Fluorescence Detector (TA-FD) and the atmosphere is crucial for precise analysis of Ultra High Energy Cosmic Rays (UHECRs) using the atmospheric fluorescence method. This presentation focuses on two key aspects of calibration: the pointing direction of the TA-FD and the atmospheric transparency as measured by the Vertical Aerosol Optical Depth...
Ultra High-Energy Cosmic Rays (UHECRs) are expected to interact extensively with the
cosmic microwave background (CMB) and the extragalactic background light (EBL),
generating secondary particles such as gamma rays and neutrinos. These secondary
particles create a guaranteed diffuse background of photons in the GeV-TeV energy
range and neutrinos in the PeV-EeV range. Notably, while UHECRs...
There's a reported correlation between the arrival directions of ultra-high-energy cosmic rays (UHECRs) and nearby starburst galaxies (SBGs). Auger collaboration (2018, 2022) reported a ~4 sigma significance correlation with SBGs, and the Telescope Array (TA) experiment also shows consistent results (TA collaboration 2018). The effects of the magnetic field on UHECR flux would be mandatory to...
We report on the cosmic ray mass composition measured by the Telescope Array Low-energy Extension (TALE) hybrid detector. The TALE detector began operations in 2017 with 10 high-elevation fluorescence telescopes and a surface detector (SD) array of 80 scintillation counters, including 40 with 400 m spacing and 40 with 600 m spacing. In 2023, we constructed a new array made up of 50 SDs with a...
Segmented muon detectors, such as the Underground Muon Detector (UMD) of the Pierre Auger Observatory, can suffer from overcounting due to inclined muons generating signals in two adjacent segments. This effect, known as corner-clipping, introduces a bias in the muon estimator that increases with the zenith angle. To correct for this, the common approach is to parameterize the bias as a...
The Pierre Auger Observatory (Auger) and the Telescope Array (TA), located, respectively, in the Southern and Northern hemispheres, are the largest ultra-high-energy cosmic ray (UHECR) observatories. The data sets of unprecedented statistics collected by the two observatories offer a unique opportunity to search for the differences between the UHECR properties in the mostly complementary sky...
The origins of Ultra High Energy Cosmic Rays (UHECRs) remain unclear. A significant difficulty in identifying their sources is the complex deflection of charged particles by galactic and intergalactic magnetic fields. Our goal is to detect high-energy neutrinos produced through interactions between UHECRs and matter near astrophysical objects, to help elucidate their origins. In this study, we...
On their journey from their sources to Earth, electrically-charged cosmic rays are deflected by magnetic fields.
While small-scale magnetized structures have no impact on the propagation of ultra-high energy cosmic rays, they can have an impact on our reconstruction of the large-scale magnetic field obtained from synchrotron and Faraday rotation data. In this context, the Local Bubble, a...
Using radio detectors for cosmic rays is a very appealing approach, as they are cost-effective, have a nearly 100% duty cycle and can directly probe the electromagnetic component of extensive air showers. However, reconstructing the electric field from the measured voltages in an antenna by unfolding the antenna response comes with several challenges. Due to the noisiness of the signal, it is...
Accurate reconstruction of Ultra-High-Energy Cosmic Ray (UHECR) parameters is crucial for understanding their origins and composition. We present a newly developed Deep Neural Network (DNN) approach based on the AixNet architecture for reconstructing UHECR parameters from Telescope Array surface detector (SD) data. This model reconstructs key parameters, including energy, arrival direction,...
Recent years have brought a number of breakthroughs and discoveries in high-energy astrophysics. Many of these advances are related to transient phenomena and involve all known cosmic messengers from radiation across the full electromagnetic spectrum to high-energy neutrinos, gravitational waves, and cosmic rays. Due to their high sensitivity and increasingly optimized response to transient...
The Global Spline Fit is a data-driven parameterization of cosmic-ray flux and mass composition. It combines direct and indirect measurements of cosmic-ray flux of individual elements from 1 GeV to $10^{11}$ GeV, considering their uncertainties. At lower energies, the flux is corrected to the local interstellar spectra using the individual data-taking periods of the experiments. The systematic...
GRAND (the Giant Radio Array for Neutrino Detection) is a proposed next-generation observatory of ultra-high-energy (UHE) neutrinos, cosmic rays, and gamma rays of cosmic origin, with energies exceeding about 100 PeV. GRAND is a collection of large-scale ground arrays of self-triggered radio antennas that target the radio emission from extensive air showers initiated by UHE particles. Three...
The Giant Radio Array for Neutrino Detection (GRAND) is an envisioned next-generation observatory designed to detect ultra-high-energy (UHE) neutrinos, cosmic rays, and gamma rays, with energies exceeding 100 PeV. GRAND will consist of multiple large-scale ground arrays of self-triggered radio antennas, aiming to detect the radio emission from extensive air showers initiated by these UHE...
The field of air shower physics is dedicated to understanding the development of cosmic-ray interactions with the Earth's atmosphere. However, it faces a significant challenge regarding the muon content of extensive air showers (EAS) observed by several cosmic-ray experiments, such as the Pierre Auger Observatory. Current simulations employing state-of-the-art hadronic interaction models yield...
In this talk, we discuss the propagation of ultra-high energy cosmic rays (UHECRs), and
the resultant production of secondary diffuse neutrinos, in the presence of self-induced
confinement due to the excitation of the Non-Resonant Streaming Instability (NRSI)
near their sources.
UHECRs leaving their sources may induce a large electric current in the near-source
region, sufficient to...
Flares produced by some classes of astrophysical objects may be sources of some ultra-high-energy particles, which, if they are neutral, would group into clusters, highly correlated in space and time. Identification of such clustering in cosmic-ray data would provide important evidence for possible existence of neutral particles of ultra-high-energies (UHE) and could potentially help identify...
The Fluorescence detector Array of Single-pixel Telescopes (FAST) is a next-generation cosmic ray experiment aiming to observe cosmic rays above 10$^{19}$ eV with unprecedented statistics. To achieve this, FAST will utilize low-cost, easily deployable, autonomous fluorescence telescopes spread over a detecting area an order of magnitude larger than those of current observatories. We present...
The next generation of cosmic and gamma ray experiments plans to answer persisting fundamental questions in ultra-high-energy astroparticle physics: what sources and acceleration mechanisms can produce the most energetic particles ever measured, with energies greater than 10 EeV? Are there any photons produced in our galaxy at 30 PeV? A proposed measurement technique for next generation...
The theoretical consideration of magnetic monopoles in astrophysical contexts introduces the possibility of their efficient acceleration to extreme energies by large-scale magnetic fields, a mechanism that could potentially produce Ultra-High-Energy (UHE) photons. However, there exists a theoretical argument, formulated within the quantum theory of the electric charge, that raises questions...
Ultra-high energy cosmic rays impinging on the Earth’s atmosphere offer a unique opportunity to probe hadronic interactions at the highest energies through measurements of the extensive air showers they generate. In this work, we introduce a semi-analytic mapping between new macroscopic variables describing the first ultra-high-energy proton-air interaction and the shower-to-shower values of...
The Telescope Array Low-energy Extension (TALE) experiment is a project that extends the Telescope Array (TA) experiment to observe cosmic rays with energies above 1016.5 eV using 10 fluorescence detectors (FDs) and 80 surface detectors (SDs). The TALE-infill SD array, consisting of 50 SDs arranged in a grid pattern with 100-meter spacing, has been installed to extend observations...
The TA Low-energy Extension (TALE) experiment extends the reach of the TA experiment on the low-energy side to below $10^{16}$ eV. A primary objective of TALE is to study the transition from galactic to extragalactic cosmic rays. The TALE detector is a hybrid observatory composed of fluorescence telescopes and a surface detector array of scintillation counters. The surface detectors are...
The depth of the shower maximum, $X_\mathrm{max}$, as observed with the fluorescence telescopes, is one of the key most sensitive observables for probing the interaction characteristics and primary composition of ultra-high-energy cosmic rays. Nevertheless, the accurate measurement of the interaction cross-section poses a significant challenge due to the inherent limitations of standard...
Data from multiple experiments suggest that the current interaction models used in Monte Carlo simulations do not correctly reproduce the hadronic interactions in air showers produced by ultra-high-energy cosmic rays (UHECR).We have created a large library of UHECR simulations where the interactions at the highest energies are slightly modified in various ways – but always within the...
Despite their low individual luminosity, Fanaroff-Riley Type 0 (FR0) radio galaxies have emerged as potentially significant contributors to the observed flux of ultra-high-energy cosmic rays (UHECRs, E$>$10$^{18}$ eV) due to their substantial prevalence in the local universe. Outnumbering more powerful FR radio galaxies by approximately fivefold within redshifts of z$<$0.05, FR0s may...
Various measurements of muons in air showers using ground-based particle detector arrays have indicated a discrepancy between observed data and predictions from simulations. The IceCube Neutrino Observatory can offer unique insights into this issue. Its surface array, IceTop, measures the muon density at large lateral distances, while the deep in-ice detector provides information on...
This study focuses on identifying highly inclined muons in water-Cherenkov detectors similar to those used by the Pierre Auger Observatory using neural networks. Highly inclined muons, which are distinctive signatures of air showers induced by neutrinos or cosmic rays arriving at significant inclinations, offer a lower background rate compared to less inclined atmospheric particles. We explore...
Neutrinos act as probes of hadronic processes and offer a distinctive view into their astrophysical origins at high energies. When reaching energies ≳PeV, tau neutrino interactions within the Earth can produce a significant flux of tau-leptons. These tau-leptons subsequently decay, generating upward-moving extensive air showers (EAS). Using the Earth as a target for neutrinos and the...
Gravitational wave sources detected by LIGO Virgo and Kagra are primarily BBH but also there arre several detections of events that include neutron stars. Theses objects are primary candidates for multimessenger sources as there is plenty of matter available. I will review the current status of the observations, and the constraints on their rate density. The turbulent environment around such...
Active galactic nuclei (AGN) are among the main candidates for ultra-high-energy cosmic ray (UHECR) sources. However, while theoretical and some phenomenological works favor AGNs as the main sources, recent works have shown that using the very-high-energy (VHE) γ-ray flux as a proxy for the UHECR flux leads to a bad agreement with data. In this context, the energy spectrum and composition data...
From the detection by John Linsley (1963) of a cosmic ray of energy ∼ 1.0 × $10^{20}$ eV to the recent detection (2023) of the shower called Amaterasu by the Telescope Array experiment at ∼ 2.4 × $10^{20}$ eV (i.e. 40 joules!), our community has been striving to build the largest astroparticle observatories in the world to identify the sources of ultra-high-energy protons and nuclei. The...
Strange quark stars are hypothetical objects composed of strange quark matter (SQM). SQM is unstable on the star's surface. Oscillations of strange stars, including radial oscillations, can very efficiently lead to the release of energy. Such oscillations could be excited in compact binary star systems due to tidal forces. The excitation energy depends on both the mass of the strange star and...
The combination of fluorescence and surface detectors at the Pierre Auger Observatory offers unprecedented precision in testing models of hadronic interactions at center-of-mass energies around 100 TeV and beyond. However, for some time, discrepancies between model predictions and measured air-shower data have complicated efforts to accurately determine the mass composition of...
Since 2010, the international JEM-EUSO (Joint Exploratory Missions for Extreme Universe Space Observatory) collaboration has been developing an ambitious program with the support of major International and National Space Agencies and research funding institutions, to enable ultra-high-energy cosmic ray (UHECR) and high-energy neutrino observations from space. Its main objective is to develop a...
Dark Matter (DM) existence is a milestone of the cosmological standard model and, yet its nature remains a complete mystery. In this contribution, I investigate an original way to probe the properties of sub-GeV DM particle candidates, by exploiting the cosmic-ray (CR) transport inside starburst nuclei (SBNi). Indeed, SBNi are considered CR reservoirs, thereby being able to trap CRs for $\sim...
In order to obtain a sufficient number of observational events to clarify the origin of ultra high energy cosmic rays, a large-scale observatory is required. Currently, next-generation detectors are being developed for this purpose. The CRAFFT project focuses on developing fluorescence detectors that can be produced and operated at low cost. In this presentation, we will report on the status...
High-altitude balloon-borne detectors offer a unique perspective on the extensive air showers induced by very high-energy cosmic rays. By placing a detector on the edge of the atmosphere (33 km altitude), fluorescence and Cherenkov light produced by high-altitude horizontal air showers (HAHAS) can be observed. These HAHAS develop in a rarefied atmosphere resulting in the shower’s energy being...
It was recently shown that models where UHECR sources are transients that occur proportionally to the starformation rate of each galaxy can roughly reproduce the intermediate-scale overdensities observed in the UHECR arrival directions at $E\gtrsim$40 EeV. Based on that, we explore the prospects of a likelihood-based fit of such models to event-level data from the Pierre Auger Observatory....
Air-Shower universality describes the regularity in the longitudinal, lateral, and energy distributions of electromagnetic shower particles, as motivated by solutions of the cascade equations. To reconstruct air-shower observables from ultrahigh-energy cosmic rays, we employ a universality-based model of shower development that incorporates hadronic particle components. Depending on the input...
Over the past two decades, astroparticle experiments have observed an excess of muons in air shower measurements compared to predictions based on hadronic interaction models calibrated to LHC data. This discrepancy impacts the interpretation of mass composition studies and has deep implications regarding our understanding of hadronic processes at the highest energies. In this work, we propose...
IceCube-Gen2, the next generation extension of the IceCube Neutrino Observatory at the South Pole, offers a unique scientific potential for cosmic-ray physics at PeV to EeV energies complementing the main science case of neutrino astronomy. The cosmic-ray science case will be enabled by a surface array on top of an extended optical array deep in the polar ice. The optical array measures TeV...
We searched for magnetic structures known as multiplets caused by magnetic deflection of ultra high energy cosmic rays in the 15 years of cosmic ray observation data from the surface detectors of the Telescope Array (TA) experiment. In this data analysis, we specifically investigated the TA hotspot in detail by using data above 57 EeV and applying the maximum likelihood estimation method to...
Astrophysical neutral particles, such as neutrons, provide a unique opportunity to trace back directly to their origins since they are not deflected by magnetic fields after being produced through interactions of charged cosmic rays in the immediate vicinity of their acceleration sites. Neutrons, being unstable particles, undergo decay, but at high energies they can travel considerable...
The Pierre Auger Observatory, as a key actor in multi-messenger astronomy, is playing a crucial role in searching for and following-up cosmic phenomena across different channels. Data from the Observatory have been utilized for nearly 20 years to search for showers induced by Ultra-High-Energy (UHE) neutrinos with energies exceeding 0.1 EeV. Neutrino-induced showers at high zenith angles are...
The Pierre Auger Observatory, the largest air-shower experiment in the world designed to investigate ultra-high-energy (UHE, $E > 10^{17}$ eV) cosmic rays, offers unparalleled sensitivity to UHE photons. They are expected to originate from the interaction of UHE cosmic rays with background radiation fields, as well as from more exotic processes like the decay of hypothetical super-heavy dark...
We present the design and science case for a new array of radio antennas to be located at the Pierre Auger Observatory. Six stations of three SKALA antennas each will be deployed around a single water-Cherenkov surface detector triggering the radio readout. The planned antenna layout will allow for the detection of cosmic rays above a few tens of PeV, and reach full efficiency for vertical air...
The interactions of ultra-high energy cosmic rays (UHECRs) in astrophysical scenarios are in general of stochastic nature. Whether the targets are photon fields (photohadronic) or other nuclei (hadronic), the outcomes of a sequence of interactions are currently obtained via Monte Carlo simulations since the compound distributions are not known. The reason is that, although the outcomes of...
The IceCube Collaboration has recently reported compelling evidence of high energy neutrino emission from NGC 1068, and mild excesses for NGC 4151 and CGCG420- 015, local Seyfert galaxies. This has increased the interest along neutrino emission from hot corona surrounding the super massive black holes of Seyfert Galaxies. In this contribution, I demonstrate that these sources are consistent...
The Pierre Auger Observatory, located near Malargüe in Mendoza, Argentina, is the largest cosmic-ray detector in existence, covering an area of $3000\,\mathrm{km}^2$. The upgraded Observatory, in phase II of operations, consists of a surface array of 1660 stations combining water Cherenkov, scintillator, and radio detectors. A subset of stations also includes underground muon detectors....
Knowledge of the coherent Galactic magnetic field (GMF) is important for many purposes, especially for interpreting the arrival directions of ultra-high-energy cosmic rays (UHECRs). For more than a decade, the community has relied mainly on a single model of the coherent field (Jansson-Farrar, JF12). Recently, a suite of models has been developed (Unger-Farrar, UF23) based on the latest data...
We discuss the remarkable potential of neutrino and gamma-ray data from the Pierre Auger Observatory to constrain physics beyond the Standard Model. This analysis emphasizes the Observatory's capabilities in testing and potentially falsifying models of super-heavy dark matter, based on the early-universe generation of super-heavy particles, as well as models of broken Lorentz invariance, which...
The Pierre Auger Observatory offers a unique research infrastructure for advancing astroparticle physics. It integrates various detection techniques to study extensive air showers, including a surface array of water-Cherenkov detectors, scintillators (both surface and underground), radio antennas, and 27 fluorescence telescopes. This comprehensive setup enables precise measurement of...
During almost 20 years of regular data acquisition, the Pierre Auger Observatory, the world's largest facility for measuring ultrahigh-energy cosmic rays, has collected a vast and diverse amount of data covering complementary fields of research from astroparticle and fundamental physics to space weather science.
The Pierre Auger Collaboration has embraced the concept of open access
to...
The Southern Wide-field Gamma Ray Observatory (SWGO) is a collaboration to develop and construct an air-shower array for ground-based gamma ray observatory in the Southern Hemisphere. The plan is to improve on or at least equal the performance of similar observatories, like LHAASO or HAWC. SWGO will extend the sky visible to this type of instrument to the Southern Hemisphere. The detector will...
Venus' atmosphere -specifically its clouds buoyed up 40 to 60~km above the surface- has long been suspected to encompass a biosphere where Earth-like living organisms could grow and flourish. This idea has been recently rekindled by the observation
(signal-to-noise ratio of about 15$\sigma$) of a phosphine (PH$_3$) absorption-line profile against the thermal background from deeper, hotter...
We present the first study to investigate ultra-fast outflows (UFOs) of active galactic nuclei as potential sites for the production of the highest-energy cosmic rays, focusing on cosmic-ray nuclei, a previously unexplored aspect. These mildly-relativistic large-scale outflows, with velocities reaching up to half the speed of light, are ubiquitous in active galactic nuclei. We numerically...
We investigate the propagation of ultraheavy (UH) nuclei as ultrahigh-energy cosmic rays (UHECRs). We show that their energy loss lengths at $\lesssim300$~EeV are significantly longer than those of protons and intermediate-mass nuclei and that the highest-energy cosmic rays with energies beyond $\sim100$~EeV, including the Amaterasu particle, may originate from such UH-UHECRs. We derive...
The Pierre Auger Observatory is equipped with a sophisticated atmospheric monitoring system that has been operating smoothly for about 20 years. E.g., it provides hourly corrections to cosmic-ray data recorded by the Fluorescence Detector as well as updates on cloud conditions, ensuring high quality data. In recent years, new tools have been integrated in addition to the standard instruments:...
Contrary to what had been hoped a quarter of a century ago, pointing astronomy with ultra-high-energy cosmic rays (UHECR) has remained elusive, despite considerable increase in statistics. The reason is most probably due to much larger deflections than anticipated under the assumption that most UHECRs would be protons, as well as a possibly much larger number of contributing sources. While it...
