Cosmic Rays Research Articles

Unusual Forbush Decreases and Geomagnetic Storms on 24 March, 2024 and 11 May, 2024

As the current solar cycle 25 progresses and moves towards solar maxima, solar activity is increasing and extreme space weather events are taking place. Two severe geomagnetic storms accompanied by two large Forbush decreases in galactic cosmic ray intensity were recorded in March and May, 2024. More precisely, on 24 March 2024, a G4 (according to the NOAA Space Weather Scale for Geomagnetic Storms) geomagnetic storm was registered, with the corresponding geomagnetic indices Kp and Dst equal to 8 and −130 nT, respectively. On the same day, the majority of ground-based neutron monitor stations recorded an unusual Forbush decrease. This event stands out from a typical Forbush decrease because of its high amplitude decrease phase and rapid recovery phase, i.e., 15% decrease and an extremely rapid recovery of 10% within 1.5 h, as recorded at the Oulu neutron monitor station. Furthermore, on 10–13 May 2024, an unusual G5 geomagnetic storm (geomagnetic indices Kp = 9 and Dst = −412 nT) was registered (the last G5 storm had been observed in 2003). In addition, the polar neutron monitor stations recorded a Ground Level Enhancement (GLE74) during the recovery phase of a large Forbush decrease of 15%, which started on 10 May 2024. In this study, a detailed analysis of these two severe events in regard to the accompanying solar activity, interplanetary conditions and solar energetic particle events is provided. Moreover, the results of the NKUA “GLE Alert++ system”, the NKUA/IZMIRAN “FD Precursory Signals” method and the NKUA “ap Prediction tool” concerning these events are presented.

The Ziré instrument onboard the NUSES space mission

The Ziré experiment is an instrument on board the NUSES (NeUtrino and Seismic Electromagnetic Signals) satellite dedicated to test new techniques for the study of low energy cosmic radiation, Sun–Earth environment, space weather and magnetosphere–ionosphere–lithosphere coupling (MILC). Ziré will consist of a fiber tracker, a stack of plastic scintillators, an array of LYSO crystals and an anticoincidence system. A dedicated Low Energy Module (LEM) will extend the sensitive energy range down to the MeV scale for charged particles. In this work, a general overview of the Ziré payload will be given, together with a focus on the design and the review of dedicated tests on the first prototype.

A new perspective on the diffuse gamma-ray emission excess* *Supported by the National Natural Science Foundation of China (12105292, 12175248, 12393853)

The Large High-Altitude Air Shower Observatory (LHAASO) recently published measurements of diffuse Galactic gamma-ray emission (DGE) in the 10−1000 TeV energy range. The measured DGE flux is significantly higher than the expectation from hadronic interactions between cosmic rays (CRs) and the interstellar medium. This excess has been proposed to originate from unknown extended sources produced by electron radiation, such as pulsar wind nebulae or pulsar halos (PWNe/halos). In this paper, we propose a new perspective to explain the DGE excess observed by LHAASO. The masking regions used in the LHAASO DGE measurement may not fully encompass the extended signals of PWNe/halos. By employing a two-zone diffusion model for electrons around pulsars, we find that the DGE excess in most regions of the Galactic plane can be well explained by the signal leakage model under certain parameters. Our results indicate that this signal leakage from known sources and contributions from unresolved sources should be considered as complementary in explaining the DGE excess.

Revealing the Production Mechanism of High-energy Neutrinos from NGC 1068

The detection of high-energy neutrino signals from the nearby Seyfert galaxy NGC 1068 provides us with an opportunity to study nonthermal processes near the center of supermassive black holes. Using the IceCube and latest Fermi-LAT data, we present general multimessenger constraints on the energetics of cosmic rays and the size of neutrino emission regions. In the photohadronic scenario, the required cosmic-ray luminosity should be larger than ∼1%−10% of the Eddington luminosity and the emission radius should be ≲15R S in low-β plasma and ≲3R S in high-β plasma. The leptonic scenario overshoots the NuSTAR or Fermi-LAT data for any emission radii we consider, and the required gamma-ray luminosity is much larger than the Eddington luminosity. The beta-decay scenario also violates not only the energetics requirement but also gamma-ray constraints, especially when the Bethe–Heitler and photomeson production processes are consistently considered. Our results rule out the leptonic and beta-decay scenarios in a nearly model-independent manner and support hadronic mechanisms in magnetically powered coronae if NGC 1068 is a source of high-energy neutrinos.

Approach for composition measurement of cosmic rays using the muon-to-electron ratio observed by LHAASO-KM2A

Approach for composition measurement of cosmic rays using the muon-to-electron ratio observed by LHAASO-KM2A

Influence of galactic cosmic ray flux on extreme rainfall events in Greece and Libya

The Galactic Cosmic Rays (GCR) flux can contribute to the formation of condensation nuclei (CN), radionuclides, and other particles, which in turn influence the formation of rain and extreme weather events. The aim of this analysis was to investigate the possible influence of GCR flux on the extreme rainfall events that occurred in Greece and Libya in September 2023. We used time series data for GCR, rainfall estimates from ERA5, and Sea Surface Temperature (SST) for the period between September 1, 2023, and September 11, 2023. The results revealed a negative correlation between GCR and SST of −0.807 (Greece) and −0.828 (Libya), and a positive correlation between precipitation and SST of +0.972 (Greece) and +0.998 (Libya). The GCR flux and SST accounted for approximately 60.52% and 34.53% of the extreme event in Greece, and 33.71% and 65.96% in Libya, respectively. These statistical results indicate that GCR flux contributed to the formation of the extreme precipitation event that caused significant destruction in Greece and Libya in September 2023.

Millicharged particles from proton bremsstrahlung in the atmosphere

Light millicharged particles can be copiously produced from meson decays in cosmic ray collisions with the atmosphere, leading to detectable signals in large underground neutrino detectors. In this paper we study a new channel for generating atmospheric millicharged particles, the proton bremsstrahlung process. We find that the proton bremsstrahlung process leads to a significantly higher flux of millicharged particles compared to meson decays and, for certain masses, results in a one-order-of-magnitude improvement in the flux. Consequently, Super-K constraints on ε2 for sub-GeV MCPs are improved by half order of magnitude. We further note that the study on the proton bremsstrahlung process can be extended to a variety of new physics particle searches in atmospheric collisions and in low energy proton accelerators.

Closing the Net on Transient Sources of Ultrahigh-energy Cosmic Rays

The arrival directions of ultrahigh-energy cosmic rays (UHECRs) observed above 4 × 1019 eV provide evidence of localized excesses that are key to identifying their sources. We leverage the 3D matter distribution from optical and infrared surveys as a density model of UHECR sources, which are considered to be transient. Agreement of the sky model with UHECR data imposes constraints on both the emission rate per unit matter and the time spread induced by encountered turbulent magnetic fields. Based on radio measurements of cosmic magnetism, we identify the Local Sheet as the magnetized structure responsible for the kiloyear duration of UHECR bursts for an observer on Earth and find that the turbulence amplitude must be within 0.5–20 nG for a coherence length of 10 kpc. At the same time, the burst-rate density must be above 50 Gpc−3 yr−1 for Local Sheet galaxies to reproduce the UHECR excesses and below 5000 Gpc−3 yr−1 (30,000 Gpc−3 yr−1) for the Milky Way (Local Group galaxies) not to outshine other galaxies. For the transient emissions of protons and nuclei to match the energy spectra of UHECRs, the kinetic energy of the outflows responsible for UHECR acceleration must be below 4 × 1054 erg and above 5 × 1050 erg (2 × 1049 erg) if we consider the Milky Way (or not). The only stellar-sized transients that satisfy both Hillas’ and our criteria are long-duration gamma-ray bursts.

Plasticity of the heart in response to changes in physical activity.

The human heart is very adaptable, with chamber size, wall thickness and ventricular stiffness all modified by periods of inactivity or exercise training. Herein, we summarize the cardiac adaptations induced by changes in physical activity, ranging from bed rest and spaceflight to endurance exercise training, while also highlighting how the ageing process (a long-term model of inactivity) affects cardiac plasticity. Severe inactivity during bed rest or spaceflight leads to cardiac atrophy and ventriculo-vascular stiffening. Conversely, endurance training induces eccentric hypertrophy and enhances ventricular compliance, and can be used as an effective countermeasure to prevent adverse cardiac changes during prolonged periods of bed rest or spaceflight. With sedentary ageing, the heart undergoes concentric remodelling and irreversibly stiffens at advanced age. Specifically, older adults who initiate endurance training later in life are unable to improve ventricular compliance and diastolic function, suggesting reduced cardiac plasticity with advanced age; however, lifelong exercise training prevents age-associated cardiac remodelling and maintains cardiac compliance of older adults at a level similar to those of younger healthy individuals. Nevertheless, there are still many knowledge gaps related to cardiac remodelling and changes in cardiac function induced by bed rest, exercise training and spaceflight, as well as how these different stimuli may interact with advancing age. Future studies should focus on understanding what factors (sex, age, heritability, etc.) may influence the heart's responsiveness to training or deconditioning, as well as understanding the long-term cardiac consequences of spaceflight beyond low-Earth orbit with the added stimulus of galactic cosmic radiation.

Long-Term, Sex-Specific Effects of GCRsim and Gamma Irradiation on the Brains, Hearts, and Kidneys of Mice with Alzheimer's Disease Mutations.

Understanding the hazards of space radiation is imperative as astronauts begin voyaging on missions with increasing distances from Earth's protective shield. Previous studies investigating the acute or long-term effects of specific ions comprising space radiation have revealed threats to organs generally considered radioresistant, like the brain, and have shown males to be more vulnerable than their female counterparts. However, astronauts will be exposed to a combination of ions that may result in additive effects differing from those of any one particle species. To better understand this nuance, we irradiated 4-month-old male and female, wild-type and Alzheimer's-like mice with 0, 0.5, or 0.75 Gy galactic cosmic ray simulation (GCRsim) or 0, 0.75, or 2 Gy gamma radiation (wild-type only). At 11 months, mice underwent brain and heart MRIs or behavioral tests, after which they were euthanized to assess amyloid-beta pathology, heart and kidney gene expression and fibrosis, and plasma cytokines. Although there were no changes in amyloid-beta pathology, we observed many differences in brain MRIs and behavior, including opposite effects of GCRsim on motor coordination in male and female transgenic mice. Additionally, several genes demonstrated persistent changes in the heart and kidney. Overall, we found sex- and genotype-specific, long-term effects of GCRsim and gamma radiation on the brain, heart, and kidney.

The Mu2e Digitizer ReAdout Controller (DiRAC): Characterization and radiation hardness

The Mu2e experiment at Fermilab will search for the neutrino-less coherent conversion of a muon into an electron in the field of a nucleus. Mu2e detectors comprise a straw tracker, an electromagnetic calorimeter and a veto for cosmic rays. The calorimeter employs 1348 Cesium Iodide crystals readout by silicon photo-multipliers and fast front-end, and digitization electronics. The digitization board is named DiRAC (Digitizer ReAdout Controller) and 140 cards are needed for the readout of the full calorimeter. The DiRACs are hosted in crates located on the external surface of calorimeter disks, inside the detector solenoid cryostat and must sustain very high radiation and magnetic field so it was necessary to fully qualify it. Several version of prototypes were validated for operation in a high-vacuum (10−4 Torr) and under a 1T magnetic field. An extensive radiation hardness qualification campaign, carried out with photons, 14 MeV neutron beams, and 200 MeV protons, certified the DiRAC design to sustain doses up to 12 krad, neutron fluences up to ∼10111MeV neq/cm2, and very low occurrences of single-event effects. The qualification campaigns and quality assurance procedures will be reviewed.

Convolutional Neural Network Processing of Radio Emission for Nuclear Composition Classification of Ultra-High-Energy Cosmic Rays

Ultra-high-energy cosmic rays (UHECRs) are extremely rare energetic particles of ordinary matter in the Universe, traveling astronomical distances before reaching the Earth’s atmosphere. When primary cosmic rays interact with atmospheric nuclei, cascading extensive air showers (EASs) of secondary elementary particles are developed. Radio detectors have proven to be a reliable method for reconstructing the properties of EASs, such as the shower’s axis, its energy, and its maximum (Xmax). This aids in understanding fundamental astrophysical phenomena, like active galactic nuclei and gamma-ray bursts. Concurrently, data science has become indispensable in UHECR research. By applying statistical, computational, and deep learning methods to both real-world and simulated radio data, researchers can extract insights and make predictions. We introduce a convolutional neural network (CNN) architecture designed to classify simulated air shower events as either being generated by protons or by iron nuclei. The classification achieved a stable test error of 10%, with Accuracy and F1 scores of 0.9 and an MCC of 0.8. These metrics indicate strong prediction capability for UHECR’s nuclear composition, based on data that can be gathered by detectors at the world’s largest cosmic rays experiment on Earth, the Pierre Auger Observatory, which includes radio antennas, water Cherenkov detectors, and fluorescence telescopes.

The Study of the Association between the Solar Wind Parameter and Cosmic Ray Intensity to a Severe Geomagnetic Storm (-350 < Dst ≤ -200 nT) during Solar Cycles 24 and 25

The Study of the Association between the Solar Wind Parameter and Cosmic Ray Intensity to a Severe Geomagnetic Storm (-350 < Dst ≤ -200 nT) during Solar Cycles 24 and 25

Computer modeling of a new type galactic cosmic rays simulator

A new type of a galactic cosmic rays (GCR) simulator, provided at the JINR Laboratory of Radiation Biology, is potentially capable of generating a complex radiation field with inclusions of a variety of ions with a wide energy range and with required abundance at the charged particle accelerators. This complex multicomponent radiation field simulates radiation environment inside a spacecraft during an interplanetary flight, for example, to Mars. The article provides an analytical description of the GCR simulator as well as a description of a specially developed software that enables selection of necessary parameters of a simulator model for creating relevant mixed radiation conditions. The software implements processing of data obtained with Monte Carlo-based FLUKA and PHITS programs, fitting and optimization of model parameters as well as data visualization tools.

Formation of ions under the action of cosmic rays in humid air

The processes of ion formation in humid tropospheric air under the action of cosmic rays are considered. In this case, positive and negative cluster ions appear. For this analysis, a kinetic model was developed that includes 55 components and 161 reactions. The calculation was carried out using the KINET software package. It is shown that the ionization of air by cosmic rays at altitudes of 5–35 km leads to the formation of plasma consisting mainly of NH4+⋅NH3⋅H2O, H+⋅(H2O)4 and O2−⋅(H2O)2 ions. The maximum concentrations of ions under conditions of minimum magnetic rigidity are observed at altitudes from 10 to 18 km. These results differ sharply from the calculation results obtained for the dry air model.

Anisotropic Forbush decrease of 24 March 2024: First look

A strong Forbush decrease, i.e., suppression of the flux of galactic cosmic rays recorded on Earth, was observed by the global network of ground-based neutron monitors (NMs) on 24–25 March 2024. The decrease was very unusual as characterised by so rapid recovery that a false Ground-level enhancement (GLE) alarm was produced by the corresponding warning systems. Here we present the first comprehensive collection and analysis of the available data for this event. The event was highly anisotropic as exhibited in a 3-h spread of the deep-phase timing for different NMs. The anisotropy was focused nearly at the anti-sunward direction with a narrow cone of 20–30°. The heliospheric situation leading to this unusual Forbush decrease was quite complex. An analysis of first look records was performed, considering the stations acceptance, taking into account the complex geomagnetic conditions. A leader fraction analysis indicates that the recovery phase of the event was rigidity-independent and had essentially the same spectral shape as the pre-event period. A summary of the solar-terrestrial phenomena is provided to assist in future work on modelling this complex event.

The role of point defect reconstructions and polycyclic aromatic hydrocarbons in silicate dust preservation

ABSTRACT Forsterite is a primary constituent of interstellar dust and planetary systems. It is believed to originate from the outflows of oxygen-rich stars and undergo further processing within the interstellar medium through the action of cosmic rays and shocks. Under these harsh conditions, point defects may form, such as MgO Schottky vacancies. These vacancies can then undergo atom reconstruction as part of a chemical process to maintain the system’s crystalline structure. Polycyclic aromatic hydrocarbons (PAHs) are ubiquitously observed interstellar molecules and are thought to form through gas-phase reactions akin to sooting flames. However, their role and impact on dust stability remain unknown. In this study, we employ an atomistic artificial-intelligence-based method, surrogate machine learning trained directly by density functional theory. Specifically, we utilize gofee (global optimization with first-principles energy expressions) to predict possible reconstructions of MgO vacancies on a crystalline forsterite (010) surface as an important component of interstellar dust and planetary systems. We identify nine possible reconstructions involving the formation of unbound Si and O atoms. We investigate their energy stability and find that the reconstruction of Si–O atoms stabilizes the vacancy by about 0.54 eV. Additionally, if PAHs bind with the unbound O and Si atoms of the vacancy, the vacancy is stabilized by approximately 1.76 eV. We demonstrate that PAHs, along with the reconstruction of unbound atoms on the dust surface, affect the stability of the dust, which might open up avenues for diverse chemistry.

Real-time portable muography with Hankuk Atmospheric-muon Wide Landscaping : HAWL

Cosmic ray muons prove valuable across various fields, from particle physics experiments to non-invasive tomography, thanks to their high flux and exceptional penetrating capability. Utilizing a scintillator detector, one can effectively study the topography of mountains situated above tunnels and underground spaces. The Hankuk Atmospheric-muon Wide Landscaping (HAWL) project successfully charts the mountainous region of eastern Korea by measuring cosmic ray muons with a detector in motion. The real-time muon flux measurement shows a tunnel length accuracy of 6.0%, with a detectable overburden range spanning from 8 to 400 meter-water-equivalent depth. This is the first real-time portable muon tomography.

Teraelectronvolt gamma-ray emission near globular cluster Terzan 5 as a probe of cosmic ray transport

Teraelectronvolt gamma-ray emission near globular cluster Terzan 5 as a probe of cosmic ray transport

Formation and annihilation of bulk recombination-active defects induced by muon irradiation of crystalline silicon

Muons are part of natural cosmic radiation but can also be generated at spallation sources for material science and particle physics applications. Recently, pulsed muons have been used to characterize the density of free charge carriers in semiconductors and their recombination lifetime. Muon beam irradiation can also result in the formation of dilute levels of crystal defects in silicon. These crystal defects are only detected in high carrier lifetime silicon samples that are highly sensitive to defects due to their long recombination lifetimes. This work investigates the characteristics of these defects in terms of their formation, recombination activity, and deactivation. Charge carrier lifetime assessments and photoluminescence imaging have great sensitivity to measure the generated defects in high-quality silicon samples exposed to ∼4 MeV (anti)muons and their recombination activity despite the extremely low concentration. The defects reduce the effective charge carrier lifetime of both p- and n-type silicon and appear to be more detrimental to n-type silicon. Defects are created by transmission of muons through the wafer, and there are indications that slowed or implanted muons may create additional defects. In a post-exposure isochronal annealing study, we observe that annealing at temperatures of up to 450 °C does not by itself fully deactivate the defects. A recovery of charge carrier lifetime was observed when the annealing was combined with Al2O3 surface passivation, probably due to passivation of bulk defects from hydrogen from the dielectric film.