Cosmic Ray Particles Research Articles

Signposts of shock-induced magnetic field compression in star-forming environments

AbstractIn star-forming environments, shock-compressed magnetic fields occur in cloud-cloud collisions, in molecular clouds exposed to supernova remnants (SNRs), and in photo-dissociation regions (PDRs). Besides their dynamical role, they increase the cosmic ray flux above the Galactic average, and the trapped particles contribute to the heating of the shocked gas. The associated dust emission is polarized perpendicularly to the sky plane projection of the field, Bsky. In edge-on viewed shock planes, highly ordered polarization patterns are expected. In search of such a signature, the dust emission from the Orion bar (a prototypical PDR) and from a molecular cloud/SNR interface (IC443-G) was studied with a λ870μm polarimeter at the APEX (Wiesemeyer etal 2014 and references therein). While our polarization map of OMC1 confirms the hourglass shape of Bsky (e.g., Schleuning 1998, Houde etal 2004), a deep integration towards the Orion bar reveals an alignment of Bsky with the shock forming in response to the wind and to the ionizing radiation from the Trapezium cluster (Fig. 1). This structure suggests a compressed magnetic field accelerating cosmic-ray particles, a scenario proposed by [Pellegrini et al. (2009)] to explain the high excitation temperature of rotationally warm H2 and CO (Shaw et al. 2009, Peng et al. 2012, respectively).

Applying stable cosmogenic 21Ne to understand surface processes in deep geological time (107–108 yr)

This work sets out to test the applicability of stable cosmogenic 21Ne for quantifying the rates of surface processes over time scales of 107–108 yr and the potential limitations and pitfalls associated with such time spans. First, we examine several processes in addition to in-situ production during exposure that affect the final measured concentration of 21Ne. We calculate the magnitude of 21Ne produced by interaction with secondary cosmic ray particles after burial (muogenic Ne) and by non-cosmogenic sources (nucleogenic Ne). We also evaluate the fraction of 21Ne lost through diffusion out of the quartz crystal as a function of time and temperature (depth). We then apply our calculations to 21Ne concentrations measured in sediments that were deposited along the northern passive margin of Gondwana during the late Precambrian, Cambrian, and Lower Cretaceous. In light of the measured concentrations in the sediment samples, we discuss the limitations imposed by our calculations and show that 21Ne concentrations measured in Lower Cretaceous samples can be interpreted in terms of surface exposure times or average erosion rates during the time of erosion and transport. In contrast, concentrations measured in Cambrian and Precambrian samples are limited in their use as surface process indicators although they still yield valuable geological information. We conclude that this novel application of in situ stable cosmogenic nuclides holds the potential as a tool for quantifying surface processes and understanding landscape evolution during the deep geological past and provides insight into macro-scale processes that have shaped Earth over the past hundreds of millions of years.

Nautilus multi-grain model: Importance of cosmic-ray-induced desorption in determining the chemical abundances in the ISM

Context. Species abundances in the interstellar medium (ISM) strongly depend on the chemistry occurring at the surfaces of the dust grains. To describe the complexity of the chemistry, various numerical models have been constructed. In most of these models, the grains are described by a single size of 0.1 μm. Aims. We study the impact on the abundances of many species observed in the cold cores by considering several grain sizes in the Nautilus multi-grain model. Methods. We used grain sizes with radii in the range of 0.005 μm to 0.25 μm. We sampled this range in many bins. We used the previously published, MRN and WD grain size distributions to calculate the number density of grains in each bin. Other parameters such as the grain surface temperature or the cosmic-ray-induced desorption rates also vary with grain sizes. Results. We present the abundances of various molecules in the gas phase and also on the dust surface at different time intervals during the simulation. We present a comparative study of results obtained using the single grain and the multi-grain models. We also compare our results with the observed abundances in TMC-1 and L134N clouds. Conclusions. We show that the grain size, the grain size dependent surface temperature and the peak surface temperature induced by cosmic ray collisions, play key roles in determining the ice and the gas phase abundances of various molecules. We also show that the differences between the MRN and the WD models are crucial for better fitting the observed abundances in different regions in the ISM. We show that the small grains play a very important role in the enrichment of the gas phase with the species which are mainly formed on the grain surface, as non-thermal desorption induced by collisions of cosmic ray particles is very efficient on the small grains.

Probing maximum energy of cosmic rays in SNR through gamma rays and neutrinos from the molecular clouds around SNR W28

The galactic cosmic rays are generally believed to be originated in supernova remnants (SNRs), produced in diffusive shock acceleration (DSA) process in supernova blast waves driven by expanding SNRs. One of the key unsettled issue in SNR origin of cosmic ray model is the maximum attainable energy by a cosmic ray particle in the supernova shock. Recently it has been suggested that an amplification of effective magnetic field strength at the shock may take place in young SNRs due to growth of magnetic waves induced by accelerated cosmic rays and as a result the maximum energy achieved by cosmic rays in SNR may reach the knee energy instead of ∼ 200 TeV as predicted earlier under normal magnetic field situation. In the present work we investigate the implication of such maximum energy scenarios on TeV gamma rays and neutrino fluxes from the molecular clouds interacting with the SNR W28. The authors compute the gamma-ray and neutrino flux assuming two different values for the maximum energy reached by cosmic rays in the SNR, from CR interaction in nearby molecular clouds. Both protons and nuclei are considered as accelerated particles and as target material. Our findings suggest that the issue of the maximum energy of cosmic rays in SNRs can be observationally settled by the upcoming gamma-ray experiment the Large High Altitude Air Shower Observatory (LHAASO). The estimated neutrino fluxes from the molecular clouds are , however, out of reach of the present/near future generation of neutrino telescopes.

Fruit Flies Provide New Insights in Low-Radiation Background Biology at the INFN Underground Gran Sasso National Laboratory (LNGS).

Deep underground laboratories (DULs) were originally created to host particle, astroparticle or nuclear physics experiments requiring a low-background environment with vastly reduced levels of cosmic-ray particle interference. More recently, the range of science projects requiring an underground experiment site has greatly expanded, thus leading to the recognition of DULs as truly multidisciplinary science sites that host important studies in several fields, including geology, geophysics, climate and environmental sciences, technology/instrumentation development and biology. So far, underground biology experiments are ongoing or planned in a few of the currently operating DULs. Among these DULs is the Gran Sasso National Laboratory (LNGS), where the majority of radiobiological data have been collected. Here we provide a summary of the current scenario of DULs around the world, as well as the specific features of the LNGS and a summary of the results we obtained so far, together with other findings collected in different underground laboratories. In particular, we focus on the recent results from our studies of Drosophila melanogaster, which provide the first evidence of the influence of the radiation environment on life span, fertility and response to genotoxic stress at the organism level. Given the increasing interest in this field and the establishment of new projects, it is possible that in the near future more DULs will serve as sites of radiobiology experiments, thus providing further relevant biological information at extremely low-dose-rate radiation. Underground experiments can be nicely complemented with above-ground studies at increasing dose rate. A systematic study performed in different exposure scenarios provides a potential opportunity to address important radiation protection questions, such as the dose/dose-rate relationship for cancer and non-cancer risk, the possible existence of dose/dose-rate threshold(s) for different biological systems and/or end points and the possible role of radiation quality in triggering the biological response.

A Particle Module for the PLUTO Code. I. An Implementation of the MHD–PIC Equations

Abstract We describe an implementation of a particle physics module available for the PLUTO code appropriate for the dynamical evolution of a plasma consisting of a thermal fluid and a nonthermal component represented by relativistic charged particles or cosmic rays (CRs). While the fluid is approached using standard numerical schemes for magnetohydrodynamics, CR particles are treated kinetically using conventional Particle-In-Cell (PIC) techniques. The module can be used either to describe test-particle motion in the fluid electromagnetic field or to solve the fully coupled magnetohydrodynamics (MHD)–PIC system of equations with particle backreaction on the fluid as originally introduced by Bai et al. Particle backreaction on the fluid is included in the form of momentum–energy feedback and by introducing the CR-induced Hall term in Ohm’s law. The hybrid MHD–PIC module can be employed to study CR kinetic effects on scales larger than the (ion) skin depth provided that the Larmor gyration scale is properly resolved. When applicable, this formulation avoids resolving microscopic scales, offering substantial computational savings with respect to PIC simulations. We present a fully conservative formulation that is second-order accurate in time and space, and extends to either the Runge–Kutta (RK) or the corner transport upwind time-stepping schemes (for the fluid), while a standard Boris integrator is employed for the particles. For highly energetic relativistic CRs and in order to overcome the time-step restriction, a novel subcycling strategy that retains second-order accuracy in time is presented. Numerical benchmarks and applications including Bell instability, diffusive shock acceleration, and test-particle acceleration in reconnecting layers are discussed.

Observation of galactic cosmic ray spallation events from the SoHO mission 20-yr operation of LASCO

A shower of secondary Cosmic Ray (CR) particles is produced at high altitudes in the Earth's atmosphere, so the primordial Galactic Cosmic Rays (GCRs) are never directly measured outside the Earth magnetosphere and atmosphere. They approach the Earth and other planets in the complex pattern of rigidity's dependence, generally excluded by the magnetosphere. GCRs revealed by images of single nuclear reactions also called spallation events are described here. Such an event was seen on Nov. 29, 2015 using a unique LASCO C3 space coronagraph routine image taken during the Solar and Heliospheric Observatory (SoHO) mission observing uninterruptedly at the Lagrangian L1 point. The spallation signature of a GCR identified well outside the Earth's magnetosphere is obtained for the 1st time. The resulting image includes different diverging linear "tracks" of varying intensity, leading to a single pixel, this frame identifies the site on the silicon CCD chip of the coronagraph camera. There was no solar flare reported at that time, nor Coronal Mass Ejection (CME) and no evidence of optical debris around the spacecraft. More examples of smaller CR events have been discovered through the 20 years of continuous observations from SoHO. This is the first spallation event from a CR, recorded outside the Earth's magnetosphere. We evaluate the probable energy of these events suggesting a plausible galactic source. Key words: Sun: Galactic Cosmic Rays, Solar Energetic Particles, Heliosphere.

Upgrade of GLE database: Assessment of effective dose rate at flight altitude

A new database for assessment of radiation doses at cruise flight altitude in the Earth atmosphere, related to ground level enhancement (GLE) events is created under VarSiTi/SCOSTEP support and incorporated to the International ground level enhancement (GLE) database (gle.oulu.fi). The upgraded database provides, for each GLE event, where possible, information on the estimated energy/rigidity spectra of solar energetic particles and the corresponding computed effective doses at cruise flight altitude of 35 kft (10,668 m above sea level). The computations are performed for various reconstructions of solar energetic particles spectra, available in literature, thus for some events there are several results. Computations were performed using a recent model for assessment of effective dose due to cosmic ray particles, applied specifically in the polar region, where the exposure is maximal. This upgrade allows one to estimate the radiation effects at cruise flight altitude caused by major GLE events over several decades.

Supernova explosions of massive stars and cosmic rays

Most cosmic ray particles observed derive from the explosions of massive stars. Massive stars from slightly above about 10M⊙ explode as supernovae via a mechanism which we do not know yet: two not mutually exclusive main ideas are an explosion driven by neutrinos, or the magneto-rotational mechanism, in which the magnetic field acts like a conveyor-belt to transport energy outwards for an explosion. Massive stars above about 25M⊙, depending on their heavy element abundance, commonly produce stellar black holes in their supernova explosions. When two such black holes find themselves in a tight binary system they finally merge in a gigantic emission of gravitational waves, events that have now been detected. The radio interferometric data demonstrate that all of these stars have powerful magnetic winds. After an introduction (Section 1) we introduce the basic concept (Section 2): Cosmic rays from exploding massive stars with winds always show two cosmic ray components at the same time: (i) the weaker polar cap component only produced by Diffusive Shock Acceleration, showing a relatively flat spectrum, and cut-off at the knee, and (ii) the stronger 4π component, which is produced by a combination of Stochastic Shock Drift Acceleration and Diffusive Shock Acceleration, with a down-turn to a steeper power-law spectrum at the knee, and a final cut-off at the ankle. In Section 3 we use the Alpha Magnetic Spectrometer (AMS) data to differentiate these two cosmic ray spectral components; these two cosmic ray components excite magnetic irregularity spectra in the plasma, and the ensuing secondary spectra can explain anti-protons, lower energy positrons, and other secondary particles. Cosmic ray electrons of the polar cap component interact with the surrounding photon field to produce positrons by triplet pair production, and in this manner may explain the higher energy positron AMS data. In Section 4 we test this paradigm with a theory of injection based on a combined effect of first and second ionization potential; this reproduces the ratio of cosmic ray source abundances to source material abundances. We can interpret the abundance data using the relation of the total number of ions enhanced by Q02A+2/3, where Q0 is the initial degree of ionization, and A is the mass number. This interpretation implies the high temperature as observed in the winds of blue super-giant stars; it also requires that cosmic ray injection happens in the shock travelling through such a wind. Most injection happens at the largest radii before slowing down due to interaction with the environment. In Section 5 we interpret the compact radio source 41.9 + 58 in the starburst galaxy M82 as a recent binary black hole merger, with an accompanying gamma ray burst. The tell-tale observational sign is the conical cleaning sweep of the relativistic jet during the merger, observed as an open cone with very low radio emission. This can also explain the Ultra High Energy Cosmic Ray (UHECR) data in the Northern sky. Thus, by studying the cosmic ray particles, their abundances at knee energies, and their spectra, we can learn about what drives these stars to produce the observed cosmic rays.

Contribution of Supernova Remnants to CRs Secondary to Primary ratios

We study production of secondary cosmic rays (CR) in supernova remnants (SNR). The model includes reacceleration of already existing in interstellar medium secondary CR particles as well as creation of secondary CRs in nuclear collisions of accelerated protons with gas nuclei and their subsequent acceleration by SNR shock. It is shown that generation of secondary CRs in SNRs produces considerable effect in their resultant energy spectrum making it essentially flatter above 10 GeV. It is shown that calculated energy spectra of antiprotons, positrons and secondary nuclei Li, Be, B are well consistent with experimental data obtained in recent experiments PAMELA, Fermi and AMS-02.

The origin of recombining plasma and the detection of the Fe-K line in the supernova remnant W 28

Abstract Overionized recombining plasmas (RPs) have been discovered from a dozen mixed-morphology (MM) supernova remnants (SNRs). However, their formation process is still under debate. As pointed out by many previous studies, spatial variations of plasma temperature and ionization state provide clues to understanding the physical origin of RPs. We report on spatially resolved X-ray spectroscopy of W 28, which is one of the largest MM SNRs found in our Galaxy. Two observations with Suzaku XIS cover the center of W 28 to the northeastern rim where the shock is interacting with molecular clouds. The X-ray spectra in the inner regions are reproduced well by a combination of two RP models with different temperatures and ionization states, whereas that in the northeastern rim is explained with a single RP model. Our discovery of the RP in the northeastern rim suggests an effect of thermal conduction between the cloud and hot plasma, which may be the production process of the RP. The X-ray spectrum of the northeastern rim also shows an excess emission of the Fe i K α line. The most probable process to explain the line would be inner shell ionization of Fe in the molecular cloud by cosmic ray particles accelerated in W 28.

Late effects of 1H irradiation on hippocampal physiology

NASA’s Missions to Mars and beyond will expose flight crews to potentially dangerous levels of charged-particle radiation. Of all charged nuclei, 1H is the most abundant charged particle in both the galactic cosmic ray (GCR) and solar particle event (SPE) spectra. There are currently no functional spacecraft shielding materials that are able to mitigate the charged-particle radiation encountered in space. Recent studies have demonstrated cognitive injuries due to high-dose 1H exposures in rodents. Our study investigated the effects of 1H irradiation on neuronal morphology in the hippocampus of adult male mice. 6-month-old mice received whole-body exposure to 1H at 0.5 and 1 Gy (150 MeV/n; 0.35–0.55 Gy/min) at NASA's Space Radiation Laboratory in Upton, NY. At 9-months post-irradiation, we tested each animal's open-field exploratory performance. After sacrifice, we dissected the brains along the midsagittal plane, and then either fixed or dissected further and snap-froze them. Our data showed that exposure to 0.5 Gy or 1 Gy 1H significantly increased animals’ anxiety behavior in open-field testing. Our micromorphometric analyses revealed significant decreases in mushroom spine density and dendrite morphology in the Dentate Gyrus, Cornu Ammonis 3 and 1 of the hippocampus, and lowered expression of synaptic markers. Our data suggest 1H radiation significantly increased exploration anxiety and modulated the dendritic spine and dendrite morphology of hippocampal neurons at a dose of 0.5 or 1 Gy.

Internal alignment and position resolution of the silicon tracker of DAMPE determined with orbit data

The DArk Matter Particle Explorer (DAMPE) is a space-borne particle detector designed to probe electrons and gamma-rays in the few GeV to 10 TeV energy range, as well as cosmic-ray proton and nuclei components between 10 GeV and 100 TeV. The silicon–tungsten tracker–converter is a crucial component of DAMPE. It allows the direction of incoming photons converting into electron–positron pairs to be estimated, and the trajectory and charge (Z) of cosmic-ray particles to be identified. It consists of 768 silicon micro-strip sensors assembled in 6 double layers with a total active area of 6.6 m2. Silicon planes are interleaved with three layers of tungsten plates, resulting in about one radiation length of material in the tracker. Internal alignment parameters of the tracker have been determined on orbit, with non-showering protons and helium nuclei. We describe the alignment procedure and present the position resolution and alignment stability measurements.

Very High Energy Emission from the Binary System Cyg X-3

Cyg X-3 is actively studied in the entire range of the electromagnetic spectrum from the radio band to ultrahigh energies. Based on the detection of ultrahigh-energy gamma-ray emission, it has been suggested that Cyg X-3 could be one of the most powerful sources of charged cosmic-ray particles in the Galaxy. We present the results of long-term observations of the Cygnus Х-3 region at energies 800 GeV–100 TeV by the SHALON mirror Cherenkov telescope. In 1995 the SHALON observations revealed a new Galactic source of very high energy gamma-ray emission coincident in its coordinates with the microquasar Cyg X-3. To reliably identify the detected source with Cyg X-3, an analysis has been performed and an orbital period of 4.8 h has been found, which is a signature of Cyg X-3. A series of flares in Cyg X-3 at energies >800 GeV and their correlation with the activity in the X-ray and radio bands have been observed. The results obtained in a wide energy range for Cyg X-3, including those during the periods of relativistic jet events, are needed to find the connection and to understand the different components of an accreting binary system.

What humankind can expect with an inversion of Earth’s magnetic field: threats real and imagined

Earth’s global magnetic field generated by an internal dynamo mechanism has been continuously changing on different time scales since its formation. Paleodata indicate that relatively long periods of evolutionary changes can be replaced by quick magnetic inversions. Based on observations, Earth’s magnetic field is currently weakening and the magnetic poles are shifting, possibly indicating the beginning of the inversion process. This paper invokes Gauss coefficients to approximate the behavior of Earth’s magnetic field components over the past 100 years. Using the extrapolation method, it is estimated that the magnetic dipole component will vanish by the year 3600 and at that time the geomagnetic field will be determined by a smaller value of a quadrupole magnetic component. A numerical model is constructed which allows evaluating and comparing both galactic and solar cosmic ray fluxes in Earth’s magnetosphere and on its surface during periods of dipole or quadrupole domination. The role of the atmosphere in absorbing particles of cosmic rays is taken into account. An estimate of the radiation danger to humans is obtained for the ground level and for the International Space Station altitude of ∼ 400 km. It is shown that in the most unfavorable, minimum field interval of the inversion process, the galactic cosmic ray flux increases by no more than a factor of three, implying that the radiation danger does not exceed the maximum permissible dose. Thus, the danger of magnetic inversion periods generally should not have fatal consequences for humans and nature as a whole, despite dramatically changing the structure of Earth’s magnetosphere.

Search for PeVatrons at the Galactic Center using a radio air-shower array at the South Pole

The South Pole, which hosts the IceCube Neutrino Observatory, has a complete and around-the-clock exposure to the Galactic Center. Hence, it is an ideal location to search for gamma rays of PeV energy coming from the Galactic Center. However, it is hard to detect air showers initiated by these gamma rays using cosmic-ray particle detectors due to the low elevation of the Galactic Center. The use of antennas to measure the radio footprint of these air showers will help in this case, and would allow for a 24/7 operation time. So far, only air showers with energies well above 10^{16} eV have been detected with the radio technique. Thus, the energy threshold has to be lowered for the detection of gamma-ray showers of PeV energy. This can be achieved by optimizing the frequency band in order to obtain a higher level of signal-to-noise ratio. With such an approach, PeV gamma-ray showers with high inclination can be measured at the South Pole.

On space weather prediction

One of the important tasks of space weather prediction is to forecast the arrival of sub– cosmic ray particles and the onset/intensity of geomagnetic storms after solar flares. For these purposes, it is necessary to predict the onset/intensity of solar flares, to track the transit (or propagation) of coronal mass ejections (CMEs) in interplanetary space and finally to estimate the power (erg/s or w) produced by the interaction between CMEs and the magnetosphere. I find that a much more integrated and coordinated effort is needed than in the past in advancing the present space weather prediction. A few suggestions are provided for this purpose.

Theoretical Study of Extensive Air Shower Effects in Atmosphere by Simulating the Lateral structure of Several Cosmic Radiations

Extensive air showers (EAS) are a cascade of electromagnetic radiation and ionized particles that produced in the atmosphere through the interaction of a primary cosmic ray with the atom of nucleus in the air producing a huge amount of secondary particles such as X-ray, electrons, neutrons, muons, alpha particles, etc. In this work, EAS effects were demonstrated by estimating the lateral distribution function (LDF) at ultrahigh energies of the various cosmic ray particles. The LDF of charged particles such as electron and positron pair production, gamma and muons particles was simulated at ultrahigh energies 10^16, 10^18 and 10^19 eV. The simulation was carried out using an air shower simulator called AIRES system version 2.6.0. The effect of the primary particles, energies and zenith angle on the LDF of charged particles produced in the EAS was taken into account. Comparison of LDF for charged particles and experimental results gave good agreement for electron and positron pair production and muons particles at 10^19 eV for 0 and 10 zenith angles

Variations of Geomagnetic Cosmic Ray Thresholds and Their Latitudinal Behavior in the Period of Solar Disturbance in September 2005

The period of interplanetary, geomagnetic and solar disturbances of September 7–15, 2005, is characterized by two sharp increases of solar wind velocity to 1000 km/s and great Dst variation of the geomagnetic field (~140 nT). The time variations of theoretical and experimental geomagnetic thresholds observed during this strong geomagnetic storm, their connection with solar wind parameters and the Dst index, and the features of latitudinal behavior of geomagnetic thresholds at particular times of the storm were studied. The theoretical geomagnetic thresholds were calculated with cosmic ray particle tracing in the magnetic field of the disturbed magnetosphere described by Ts01 model. The experimental geomagnetic thresholds were specified by spectrographic global survey according to the data of cosmic ray registration by the global station network.

Neutron monitor count rate increase as a proxy for dose rate assessment at aviation altitudes during GLEs

Radiation exposure due to cosmic rays, specifically at cruising aviation altitudes, is an important topic in the field of space weather. While the effect of galactic cosmic rays can be easily assessed on the basis of recent models, estimate of the dose rate during strong solar particle events is rather complicated and time consuming. Here we compute the maximum effective dose rates at a typical commercial flight altitude of 35 kft (≈11 000 m above sea level) during ground level enhancement events, where the necessary information, namely derived energy/rigidity spectra of solar energetic particles, is available. The computations are carried out using different reconstructions of the solar proton spectra, available in bibliographic sources, leading to multiple results for some events. The computations were performed employing a recent model for effective dose and/or ambient dose equivalent due to cosmic ray particles. A conservative approach for the computation was assumed. A highly significant correlation between the maximum effective dose rate and peak NM count rate increase during ground level enhancement events is derived. Hence, we propose to use the peak NM count rate increase as a proxy in order to assess the peak effective dose rate at flight altitude during strong solar particle events using the real time records of the worldwide global neutron monitor network.