Acceleration Of Galactic Cosmic Rays Research Articles

Knee of the cosmic hydrogen and helium spectrum below 1 PeV measured by ARGO-YBJ and a Cherenkov telescope of LHAASO

The measurement of cosmic ray energy spectra, in particular for individual species, is an essential approach in finding their origin. Locating the "knees" of the spectra is an important part of the approach and has yet to be achieved. Here we report a measurement of the mixed Hydrogen and Helium spectrum using the combination of the ARGO-YBJ experiment and of a prototype Cherenkov telescope for the LHAASO experiment. A knee feature at 640+/-87 TeV, with a clear steepening of the spectrum, is observed. This gives fundamental inputs to galactic cosmic ray acceleration models.

STOCHASTIC ACCELERATION OF GALACTIC COSMIC RAYS BY COMPRESSIBLE PLASMA FLUCTUATIONS IN SUPERNOVA SHELLS

A theory of 2-stage acceleration of Galactic cosmic rays in supernova remnants is proposed. The first stage is accomplished by the supernova shock front, where a power-law spectrum is established up to a certain cutoff energy. It is followed by stochastic acceleration with compressible waves/turbulence in the downstream medium. With a broad spectrum for the compressible plasma fluctuations, the rate of stochastic acceleration is constant over a wide range of particle momentum. In this case, the stochastic acceleration process extends the power-law spectrum cutoff energy of Galactic cosmic rays to the knee without changing the spectral slope. This situation happens as long as the rate of stochastic acceleration is faster than 1/5 of the adiabatic cooling rate. A steeper spectrum of compressible plasma fluctuations that concentrate their power in long wavelengths will accelerate cosmic rays to the knee with a small bump before its cutoff in the comic-ray energy spectrum. This theory does not require a strong amplification of the magnetic field in the upstream interstellar medium in order to accelerate cosmic rays to the knee energy.

Observational Clues of Galactic Cosmic Rays – from X-ray Point of View

X-ray observations are the strong tool to study nonthermal phenomena in the universe. Detecting synchrotron X-rays is the direct evidence of accelerated electrons in the magnetic field, and thermal X-rays from the background plasma of the acceleration sites show us their physical parameters such as temperature, density, and so on. Recent X-ray observations show us the discrepancy of the standard model of Galactic cosmic ray acceleration in supernova remnants and pulsar wind nebulae, such as high acceleration efficiency, amplification of magnetic field on the shock, escape from the shock, and so on. In this paper, we will introduce how present X-ray observatories, and near-future X-ray observatories will, contribute the understanding Galactic cosmic ray acceleration beyond the standard model, together with radio, optical, and gamma-ray observations.

Pulsar Wind Nebulae and Cosmic Rays: A Bedtime Story

The role pulsar wind nebulae play in producing our locally observed cosmic ray spectrum remains murky, yet intriguing. Pulsar wind nebulae are born and evolve in conjunction with SNRs, which are favored sites of Galactic cosmic ray acceleration. As a result they frequently complicate interpretation of the gamma-ray emission seen from SNRs. However, pulsar wind nebulae may also contribute directly to the local cosmic ray spectrum, particularly the leptonic component. This paper reviews the current thinking on pulsar wind nebulae and their connection to cosmic ray production from an observational perspective. It also considers how both future technologies and new ways of analyzing existing data can help us to better address the relevant theoretical questions. A number of key points will be illustrated with recent results from the VHE (E > 100 GeV) gamma-ray observatory VERITAS.

Simulation on gamma ray astronomy research with LHAASO-KM2A

LHAASO (Large High Altitude Air Shower Observatory) is a large project to research on high energy gamma ray astronomy and cosmic ray physics. KM2A (one KM2 Array), one main part of the LHAASO project, using a 1km2 array composed of electron detectors (ED) and muon detectors (MD), focuses on gamma ray astronomy above 30TeV and cosmic ray physics in the “knee” region. Accurate measurement of gamma ray energy spectra above 30TeV is crucial to identify the sources as the galactic cosmic ray accelerators. Monte Carlo simulation indicates that cosmic gamma rays can be distinguished from cosmic nuclei background by using muon content in extensive air showers (EAS). With the sensitivity of about 1% of the integral flux of Crab Nebula, the high duty cycle of at least 90% and the full sky survey, the KM2A array would be very useful in discovering the galactic gamma ray sources and identifying the cosmic ray sources with gamma-ray emission. A detailed simulation is carried out for studying performance and expectation of the KM2A array in gamma ray astronomy above 30TeV.

COLLISIONLESS SHOCKS IN A PARTIALLY IONIZED MEDIUM. I. NEUTRAL RETURN FLUX AND ITS EFFECTS ON ACCELERATION OF TEST PARTICLES

A collisionless shock may be strongly modified by the presence of neutral atoms through the processes of charge exchange between ions and neutrals and ionization of the latter. These two processes lead to exchange of energy and momentum between charged and neutral particles both upstream and downstream of the shock. In particular, neutrals that suffer a charge exchange downstream with shock-heated ions generate high velocity neutrals that have a finite probability of returning upstream. These neutrals might then deposit heat in the upstream plasma through ionization and charge exchange, thereby reducing the fluid Mach number. A consequence of this phenomenon, that we refer to as the "neutral return flux", is a reduction of the shock compression factor and the formation of a shock precursor upstream. The scale length of the precursor is determined by the ionization and charge exchange interaction lengths of fast neutrals moving towards upstream infinity. In the case of a shock propagating in the interstellar medium, the effects of ion-neutral interactions are especially important for shock velocities < 3000 km/s. Such propagation velocities are common among shocks associated with supernova remnants, the primary candidate sources for the acceleration of Galactic cosmic rays. We then investigate the effects of the return flux of neutrals on the spectrum of test-particles accelerated at the shock. We find that, for shocks slower than ~3000 km/s, the particle energy spectrum steepens appreciably with respect to the naive expectation for a strong shock, namely E^-2.

Evolution of ground-based gamma-ray astronomy from the early days to the Cherenkov Telescope Arrays

Most of what we know of cosmic gamma rays has come from spacecraft, but at energies above tens of GeV it has become possible to make observations with ground-based detectors of enormously greater collecting area. In recent years one such detector type, the cluster of imaging air Cherenkov telescopes, has reached a very productive state, whilst several alternative approaches have been explored, including converted solar power collectors and novel high-altitude particle shower detectors which promised to extend the energy range covered. Key examples of development from 1952 to 2011 are followed, noting the problems and discoveries that stimulated the current work, explaining the logic of the alternative approaches that were taken. The merits of the current major Cherenkov observatories and of other viable detectors are examined and compared, with examples of the astrophysical information they are beginning to provide. The detectors are still evolving, as we still do not understand the processes onto which the gamma rays provide a window. These include the acceleration of Galactic cosmic rays (in particular, the wide-band spectra of radiation from some individual supernova remnants are still hard to interpret), the highly relativistic and variable jets from active galactic nuclei, and aspects of the electrodynamics of pulsars. Larger groups of Cherenkov telescopes still offer the possibility of an increase in power of the technique for resolvable Galactic sources especially.

Particle Acceleration in the Heliosphere: Implications for Astrophysics

There has been a remarkable discovery concerning particles that are accelerated in the solar wind. At low energies, in the region where the particles are being accelerated, the spectrum of the accelerated particles is always the same: when expressed as a distribution function, the spectrum is a power law in particle speed with a spectral index of −5, and a rollover at higher particle speeds that can often be described as exponential. This common spectral shape cannot be accounted for by any conventional acceleration mechanism, such as diffusive shock acceleration or traditional stochastic acceleration. It has thus been necessary to invent a new acceleration mechanism to account for these observations, a pump mechanism in which particles are pumped up in energy through a series of adiabatic compressions and expansions. The conditions under which the pump acceleration is the dominant acceleration mechanism are quite general and are likely to occur in other astrophysical plasmas. In this paper, the most compelling observations of the −5 spectra are reviewed; the governing equation of the pump acceleration mechanism is derived in detail; the pump acceleration mechanism is applied to acceleration at shocks; and, as an illustration of the potential applicability of the pump acceleration mechanism to other astrophysical plasmas, the pump mechanism is applied to the acceleration of galactic cosmic rays in the interstellar medium.

LHAASO-KM2A simulation

At Yangbajing, with altitude of 4300m a.s.l., the LHAASO site is an ideal location for energy spectrum and composition measurements for cosmic rays, including gamma rays, above 30TeV because developing maxima of air showers are 1-2km above the ground. One main part of LHAASO (The Large High Altitude Air Shower Observatory) project, KM2A, using a 1$km^2$ array composed of electron detectors(ED) and muon detectors(MD), focuses on gamma ray astronomy above 30TeV and cosmic ray physics in the ”knee” region. Fine measurement of gamma ray energy spectra above 30TeV is crucial to identify sources as galactic cosmic ray accelerators. Monte Carlo simulation shows that primary gamma showers can be identified event by event using muon content. The observation is background free above 50TeV. With a sensitivity of about 1% $I_{crab}$, high duty cycle of at least 90 % and full sky survey, the array would be very useful in discovering galactic gamma ray sources and identifying cosmic ray sources. A simulation is carried out for optimizing performance of the KM2A array, mainly in gamma ray astronomy above 30TeV . Moreover, compared with the report at the last ICRC, the present one considers more details of detector parameterizations and improves analys

Cosmic ray acceleration in supernova remnants and the FERMI/PAMELA data

We discuss recent observations of high energy cosmic ray positrons and electrons in the context of hadronic interactions in supernova remnants, the suspected accelerators of galactic cosmic rays. Diffusive shock acceleration can harden the energy spectrum of secondary positrons relative to that of the primary protons (and electrons) and thus explain the rise in the positron fraction observed by PAMELA above 10 GeV. We normalize the hadronic interaction rate by holding pion decay to be responsible for the gamma-rays detected by HESS from some SNRs. By simulating the spatial and temporal distribution of SNRs in the Galaxy according to their known statistics, we are able to then fit the electron (plus positron) energy spectrum measured by Fermi. It appears that IceCube has good prospects for detecting the hadronic neutrino fluxes expected from nearby SNRs.

Cosmic rays and neutrinos from supernova remnants: (or: the time when H.E.S.S. met Ginzburg and Syrovatskii)

Supernova remnants are likely to be the accelerators of galactic cosmic rays (CRs). Assuming the correctness of this hypothesis, due to Ginzburg and Syrovatskii, we analyze the quantitative connection between the observed very high energy (VHE) gamma radiation and the potentially observable VHE muon–neutrino flux. We compare different approaches to calculate the νμ flux, present a simplified method of calculation and obtain numerical results. We also discuss how to extract information on the primary CR spectrum in supernova remnants from the VHE γ-ray spectra observed by H.E.S.S. Array of imaging atmospheric Cherenkov telescopes.

Acceleration of High-Energy Cosmic Rays

The transport and acceleration of galactic cosmic rays is discussed with emphasis on the highest energies. The mechanism of diffusive shock acceleration is shown to produce a near-universal spectrum which can account for most observed cosmic rays. A quasi-perpendicular shock in general accelerates particles faster and to higher energies than a comparable quasi-parallel shock. Application of these ideas to supernova blast waves suggests that they can produce galactic cosmic rays to the knee in the spectrum, some 3 10 eV. A similar blast wave, recently identified near the galactic center could accelerate particles to an energy of some 10Z eV or higher (hereinafter Z is the charge in units of the elementary charge). It is possible that the highest-energy cosmic rays could come from the galactic center. If this is the case, there should be an enhancement of the flux of high-energy cosmic rays coming from the galactic center.

Some Aspects of Galactic Cosmic Ray Acceleration

AbstractI give a synopsis of two aspects of the Galactic Cosmic Ray (GCR) acceleration problem: the importance of the medium energy gamma-ray window, and several specific astrophysical sources which merit further investigation. NOTE: figures may be found in the on-line version only: astro-ph/0309758.

The Phenomena of High Energy Astrophysics

A brief summary of some highlights in the study of high energy astrophysical sources over the past decade is presented. It is argued that the great progress that has been made derives largely from the application of new technology to observation throughout all of the electromagnetic and other spectra and that, on this basis, the next decade should be even more exciting. However, it is imperative to observe cosmic sources throughout these spectra in order to obtain a full understanding of their properties. In addition, it is necessary to learn the universal laws that govern the macroscopic and the microscopic behavior of cosmic plasma over a great range of physical conditions by combining observations of different classes of source. These two injunctions are illustrated by discussions of cosmology, hot gas, supernova remnants and explosions, neutron stars, black holes and ultrarelativistic outflows. New interpreations of the acceleration of Galactic cosmic rays, the cooling of hot gas in rich clusters and the nature of ultrarelativistic outflows are outlined. The new frontiers of VHE γ-ray astronomy, low frequency radio astronomy, neutrino astronomy, UHE cosmic ray physics and gravitational wave astronomy are especially promising.

Transport of solar energetic particles

view Abstract Citations (36) References (46) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Transport of Solar Energetic Particles Droege, Wolfgang Abstract New developments in the understanding of the interplanetary transport of solar cosmic rays are reviewed. Based on carefully analyzed solar particle events observed on the Helios and International Sun Earth Explorer (ISEE) 3 spacecraft the relation of transport parameters to the structure of the interplanetary magnetic field is discussed. Special emphasis is given to a comparison of particle mean free paths determined from fits to intensity and anisotropy profiles with theoretical predictions derived from magnetic field spectra measured at the time of the solar particle event. Different aspects of the turbulence and wave models for the magnetic fluctuations are considered, including the effects resulting from the finite temperature of the plasma and of resonance broadening. It is found that a modified quasi-linear theory of particle scattering taking into account the effects of plasma waves propagating with respect to the average solar wind flow and the proper treatment of the dispersion relation at high wavenumber gives results which are in several cases in good agreement with particle observations in the interplanetary medium between 0.3 and 1 AU, indicating that quasi-linear theory is probably a good approximation to a full theory of solar particle transport. This has important implications for other astrophysical problems where quasi-linear theory is often used, such as the propagation and acceleration of Galactic cosmic rays and particle acceleration at shock waves. Publication: The Astrophysical Journal Supplement Series Pub Date: February 1994 DOI: 10.1086/191876 Bibcode: 1994ApJS...90..567D Keywords: Energetic Particles; Interplanetary Magnetic Fields; Interplanetary Medium; Particle Acceleration; Scatter Propagation; Solar Cosmic Rays; International Sun Earth Explorers; Transport Theory; Turbulence Models; Wave Propagation; Solar Physics; ACCELERATION OF PARTICLES; INTERPLANETARY MEDIUM; ISM: COSMIC RAYS; MAGNETOHYDRODYNAMICS: MHD; SUN: PARTICLE EMISSION; SUN: SOLAR WIND full text sources ADS |

Transport of Solar Energetic Particles

AbstractNew developments in the understanding of the interplanetary transport of solar cosmic rays are reviewed. Based on carefully analyzed solar particle events observed on the Helios and ISEE 3 spacecraft, the relation of transport parameters to the structure of the interplanetary magnetic field is discussed. Special emphasis is given to a comparison of particle mean free paths determined from fits to intensity and anisotropy profiles with theoretical predictions derived from magnetic field spectra measured at the time of the solar particle event. Different aspects of the turbulence and wave models for the magnetic fluctuations are considered, including the effects resulting from the finite temperature of the plasma and of resonance broadening. It is found that a modified quasi-linear theory of particle scattering taking into account the effects of plasma waves propagating with respect to the average solar wind flow and the proper treatment of the dispersion relation at high wavenumber gives results which are in several cases in good agreement with particle observations in the interplanetary medium between 0.3 and 1 AU, indicating that quasi-linear theory is probably a good approximation to a full theory of solar particle transport. This has important implications for other astrophysical problems where quasi-linear theory is often used, such as the propagation and acceleration of Galactic cosmic rays and particle acceleration at shock waves.Subject headings: acceleration of particles — cosmic rays — interplanetary medium — MHD — solar wind — Sun: particle emission

The Acceleration of Galactic Cosmic Rays

Although it is clear that cosmic rays are of considerable astrophysical significance we know surprisingly little about their origin(s), their mode(s) of propagation and escape from the galaxy, and even of their general properties. Practically nothing is known of the composition and energy spectra of different species at energies below about 200 MeV/nucleon as a consequence of solar modulation, which has a significant effect on the observed spectra at energies up to about 10 GeV/ nucleon. The energy spectra of ions (especially protons) appear to be well approximated by a power law (differential spectral index γ ~ 2.6) in the range 1010–1015 eV/nucleon. At higher energies (up to ~ 1020 eV/nucleon) both the spectrum and the composition of the ion component are less well known, however it is significant that the anisotropy, as evidenced from the sidereal diurnal variation, increases substantially, suggesting that perhaps an extragalactic origin must be considered.

Particle acceleration by astrophysical shocks

A new mechanism is proposed for acceleration of a power-law distribution of cosmic rays with approximately the observed slope. High-energy particles in the vicinity of a shock are scattered by Alfven waves carried by the converging fluid flow leading to a first-order acceleration process in which the escape time is automatically comparable to the acceleration time. Shocks from supernova explosions propagating through the interstellar medium can account for the acceleration of galactic cosmic rays. Similar processes occurring in extragalactic radio sources can lead to efficient in situ acceleration of relativistic electrons.