scholarly journals Cosmic Rays in the Galactic Centre

1980 ◽  
Vol 33 (1) ◽  
pp. 115
Author(s):  
Masato Yoshimori
Keyword(s):  
Energy Density ◽  
Cosmic Rays ◽  
Solar System ◽  
Molecular Clouds ◽  
Cosmic Ray ◽  
High Energy ◽  
Galactic Centre ◽  
Centre Region ◽  
Cosmic Ray Flux

The cosmic ray flux in the galactic centre region is predicted from the observed data for high energy y rays, y-ray lines and massive molecular clouds. The predicted cosmic ray fluxes above 1 GeVand below 100 MeV are two and four orders of magnitude respectively larger than the value in the neighbourhood of the solar system. The corresponding energy density of cosmic rays is estimated to be 100 eV cm- 3 ? Such a concentrated stream of cosmic rays could accelerate the dense and massive molecular clouds by transfer of their momentum.

A New Determination of Muon Directional Coupling Coefficients

1968 ◽  
Vol 1 (4) ◽  
pp. 154-157
Author(s):  
D. J. Cooke ◽  
A. G. Fenton
Keyword(s):  
Cosmic Rays ◽  
Solar System ◽  
Cosmic Ray ◽  
Accurate Information ◽  
Coupling Coefficients ◽  
The Earth ◽  
Directional Coupling ◽  
Cosmic Ray Flux ◽  
Primary Cosmic Rays

Primary cosmic rays passing through the solar system carry with them valuable information about solar and astrophysical phenomena in the form of intensity and spectral variations. In order that this information be efficiently extracted from observations of the directional cosmic-ray flux at the surface of the Earth, it is essential to have accurate information available to enable the relating of the observed secondary cosmic-ray directions of motion and intensity to those outside the range of the disturbing terrestrial influences.

scholarly journals BARYONIC DARK CLUSTERS IN GALACTIC HALOS

1996 ◽  
Vol 05 (02) ◽  
pp. 151-177 ◽  
Author(s):  
F. DE PAOLIS ◽  
G. INGROSSO ◽  
PH. JETZER ◽  
M. RONCADELLI
Keyword(s):  
Molecular Clouds ◽  
Globular Clusters ◽  
Galactic Halo ◽  
Background Radiation ◽  
Cosmic Ray ◽  
Cosmic Background Radiation ◽  
Large Magellanic Cloud ◽  
High Energy ◽  
Galactic Centre ◽  
Electromagnetic Spectrum

Besides MACHOs (Massive Astrophysical Compact Halo Objects) discovered by microlensing, cold molecular clouds (mainly of H 2) may well contribute substantially to the galactic halo dark matter. We describe a model for the formation and evolution of proto globular clusters towards either globular clusters or dark clusters of MACHOs and molecular clouds, depending on the distance from the galactic centre. Moreover, we discuss various methods to test this scenario, which rely upon observations in several bands of the electromagnetic spectrum. In particular, we estimate the γ-ray flux arising from halo molecular clouds through the interaction with high-energy cosmic-ray protons. Molecular clouds can also be detected via the absorption lines they would produce in the spectrum of stars located in the Large Magellanic Cloud and via the anisotropy they would introduce in the Cosmic Background Radiation when looking at the halo of M31 galaxy. Finally, we address the possibility of discovering MACHOs by infrared searches.

scholarly journals Formation of large NAT particles and denitrification in polar stratosphere: possible role of cosmic rays and effect of solar activity

2004 ◽  
Vol 4 (9/10) ◽  
pp. 2273-2283 ◽  
Author(s):  
F. Yu
Keyword(s):  
Cosmic Rays ◽  
Ice Cores ◽  
Cosmic Ray ◽  
High Energy ◽  
Solar Proton ◽  
Arctic Regions ◽  
Secondary Ions ◽  
Cosmic Ray Flux ◽  
Selective Formation

Abstract. The formation of large nitric acid trihydrate (NAT) particles has important implications for denitrification and ozone depletion. Existing theories have difficulty in explaining the formation of large NAT particles at temperatures above the ice frost point, which has been observed recently over wide Arctic regions. Our analyses reveal that high-energy comic ray particles might induce the freezing of supercooled HNO3-H2O-H2SO4 droplets when they penetrate these thermodynamically unstable droplets. The cosmic ray-induced freezing (CRIF) appears to be consistent with the observed, highly selective formation of NAT particles. We suggest a possible physical process behind the CRIF mechanism: the reorientation of polar solution molecules into the crystalline configuration in the strong electrical fields of moving secondary ions generated by passing cosmic rays. A simple formula connecting the CRIF rate to cosmic ray flux is derived with an undefined parameter constrained by observed NAT formation rates. Our simulations indicate that strong solar proton events (SPEs) may significantly enhance the formation of large NAT particles and denitrification. The CRIF mechanism offers a possible explanation for the observed high correlations between the thin nitrate-rich layers in polar ice cores and major SPEs, and the observed enhancement in the aerosol backscattering ratio at PSC layers shortly after an SPE and the significant precipitation velocity of the enhanced PSC layers. The key uncertainty in the CRIF mechanism is the probability (P) of freezing when a CR particle hits a thermodynamically, unstable STS droplet. Further studies are needed to either confirm or reject the CRIF hypothesis.

scholarly journals Cosmic-ray evidence for a halo

1979 ◽  
Vol 84 ◽  
pp. 485-490
Author(s):  
V. L. Ginzburg
Keyword(s):  
Synchrotron Radiation ◽  
Energy Density ◽  
Cosmic Rays ◽  
Solar System ◽  
Thermal Energy ◽  
Cosmic Ray ◽  
Gas Composition ◽  
Electron Component ◽  
Interstellar Gas ◽  
The Galaxy

Cosmic rays were discovered in 1912, but it was only about forty years later that they were found to play an important role in astronomy. Firstly, cosmic rays (including the electron component) are an important source of astronomical information, namely the cosmic synchrotron radiation. Secondly, cosmic rays are essential as energetic and dynamical factors in the galaxy and also as a source of heating and transformation of the interstellar gas composition. Suffice it to remember, for example, that near the solar system the cosmic ray energy density is about the same as the thermal energy of the interstellar gas, and the cosmic ray pressure is likewise about the same as the interstellar gas pressure. Thus, there is every reason to believe that galaxies do not consist of stars and gas only, but of cosmic rays as well.

scholarly journals Constraining the cosmic ray spectrum in the vicinity of the supernova remnant W28: from sub-GeV to multi-TeV energies

2020 ◽  
Vol 635 ◽  
pp. A40
Author(s):  
V. H. M. Phan ◽  
S. Gabici ◽  
G. Morlino ◽  
R. Terrier ◽  
J. Vink ◽  
...  
Keyword(s):  
Cosmic Rays ◽  
Molecular Clouds ◽  
Supernova Remnants ◽  
Supernova Remnant ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
Ionization Rate ◽  
High Energy ◽  
Radio Waves ◽  
X Ray

Context. Supernova remnants interacting with molecular clouds are ideal laboratories to study the acceleration of particles at shock waves and their transport and interactions in the surrounding interstellar medium. Aims. Here, we focus on the supernova remnant W28, which over the years has been observed in all energy domains from radio waves to very-high-energy gamma rays. The bright gamma-ray emission detected from molecular clouds located in its vicinity revealed the presence of accelerated GeV and TeV particles in the region. An enhanced ionization rate has also been measured by means of millimeter observations, but such observations alone cannot tell us whether the enhancement is due to low-energy (MeV) cosmic rays (either protons or electrons) or the X-ray photons emitted by the shocked gas. The goal of this study is to determine the origin of the enhanced ionization rate and to infer from multiwavelength observations the spectrum of cosmic rays accelerated at the supernova remnant shock in an unprecedented range spanning from MeV to multi-TeV particle energies. Methods. We developed a model to describe the transport of X-ray photons into the molecular cloud, and we fitted the radio, millimeter, and gamma-ray data to derive the spectrum of the radiating particles. Results. The contribution from X-ray photons to the enhanced ionization rate is negligible, and therefore the ionization must be due to cosmic rays. Even though we cannot exclude a contribution to the ionization rate coming from cosmic-ray electrons, we show that a scenario where cosmic-ray protons explain both the gamma-ray flux and the enhanced ionization rate provides the most natural fit to multiwavelength data. This strongly suggests that the intensity of CR protons is enhanced in the region for particle energies in a very broad range covering almost six orders of magnitude: from ≲100 MeV up to several tens of TeV.

scholarly journals High energy cosmic ray interactions and UHECR composition problem

2019 ◽  
Vol 210 ◽  
pp. 02001
Author(s):  
Sergey Ostapchenko
Keyword(s):  
Experimental Data ◽  
Monte Carlo ◽  
Cosmic Rays ◽  
Cosmic Ray ◽  
High Energy ◽  
Ultra High Energy ◽  
Hadronic Interactions ◽  
High Energy Cosmic Rays ◽  
Cosmic Ray Interactions ◽  
Composition Problem

The differences between contemporary Monte Carlo generators of high energy hadronic interactions are discussed and their impact on the interpretation of experimental data on ultra-high energy cosmic rays (UHECRs) is studied. Key directions for further model improvements are outlined. The prospect for a coherent interpretation of the data in terms of the UHECR composition is investigated.

scholarly journals Molecular Clouds Observed by the EGRET Gamma-Ray Telescope

1997 ◽  
Vol 170 ◽  
pp. 22-24 ◽  
Author(s):  
Seth. W. Digel ◽  
Stanley D. Hunter ◽  
Reshmi Mukherjee ◽  
Eugéne J. de Geus ◽  
Isabelle A. Grenier ◽  
...  
Keyword(s):  
Molecular Mass ◽  
Molecular Clouds ◽  
Gamma Ray ◽  
Angular Resolution ◽  
Cosmic Ray ◽  
High Energy ◽  
Background Rejection ◽  
Γ Rays ◽  
Γ Ray ◽  
Production Mechanisms

EGRET, the high-energy γ-ray telescope on the Compton Gamma-Ray Observatory, has the sensitivity, angular resolution, and background rejection necessary to study diffuse γ-ray emission from the interstellar medium (ISM). High-energy γ rays produced in cosmic-ray (CR) interactions in the ISM can be used to determine the CR density and calibrate the CO line as a tracer of molecular mass. Dominant production mechanisms for γ rays of energies ∼30 MeV–30 GeV are the decay of pions produced in collisions of CR protons with ambient matter and Bremsstrahlung scattering of CR electrons.

scholarly journals Molecular Clouds and Star Formation at Large R

1991 ◽  
Vol 144 ◽  
pp. 121-130
Author(s):  
J. Brand ◽  
J.G.A. Wouterloot
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Density Wave ◽  
Cosmic Ray ◽  
Volume Density ◽  
Kinetic Temperature ◽  
Galactocentric Distance ◽  
The Galaxy ◽  
The Mean ◽  
Cosmic Ray Flux

In the outer Galaxy (defined here as those parts of our system with galactocentric radii R>R0) the HI gas density (Wouterloot et al., 1990), the cosmic ray flux (Bloemen et al, 1984) and the metallicity (Shaver et al., 1983) are lower than in the inner parts. Also, the effect of a spiral density wave is much reduced in the outer parts of the Galaxy due to corotation. This changing environment might be expected to have its influence on the formation of molecular clouds and on star formation within them. In fact, some differences with respect to the inner Galaxy have been found: the ratio of HI to H2 surface density is increasing from about 5 near the Sun to about 100 at R≈20kpc (Wouterloot et al., 1990). Because of the “flaring” of the gaseous disk, the scale height of both the atomic and the molecular gas increases by about a factor of 3 between R0 and 2R0 (Wouterloot et al., 1990), so the mean volume density of both constituents decreases even more rapidly than their surface densities. The size of HII regions decreases significantly with increasing galactocentric distance (Fich and Blitz, 1984), probably due to the fact that outer Galaxy clouds are less massive (see section 3.3), and therefore form fewer O-type stars than their inner Galaxy counter parts. There are indications that the cloud kinetic temperature is lower by a few degrees (Mead and Kutner, 1988), although it is not clear to what extent this is caused by beam dilution.

scholarly journals Towards an anagraphical picture of high-energy Galactic neutrinos

2019 ◽  
Vol 209 ◽  
pp. 01003
Author(s):  
Antonio Marinelli ◽  
Dario Grasso ◽  
Sofia Ventura
Keyword(s):  
Short Duration ◽  
Molecular Clouds ◽  
Supernova Remnants ◽  
Cosmic Ray ◽  
High Energy ◽  
The Other ◽  
Molecular Gas ◽  
High Energy Neutrino ◽  
Neutrino Telescopes ◽  
Upper Limits

The TeV/PeV neutrino emission from our Galaxy is related to the distribution of cosmic-ray accelerators, their maximal energy of injection as well as the propagation of injected particles and their interaction with molecular gas. In the last years Interesting upper limits on the diffuse hadronic emission from the whole Galaxy, massive molecular clouds and Fermi Bubbles were set by the IceCube and ANTARES as well as HAWC and Fermi-LAT observations. On the other hand no evidence of Galactic point-like excess has been observed up to now by high-energy neutrino telescopes. This result can be related to the short duration of the PeV hadronic activity of the sources responsible for the acceleration of primary protons, possibly including supernova remnants. All these aspects will be discussed in this work.

scholarly journals Sound-wave instabilities in dilute plasmas with cosmic rays: implications for cosmic ray confinement and the Perseus X-ray ripples

2020 ◽  
Vol 493 (4) ◽  
pp. 5323-5335 ◽  
Author(s):  
Philipp Kempski ◽  
Eliot Quataert ◽  
Jonathan Squire
Keyword(s):  
Cosmic Rays ◽  
Thermal Plasma ◽  
Acoustic Waves ◽  
Cosmic Ray ◽  
High Energy ◽  
Density Fluctuations ◽  
Sound Waves ◽  
X Ray ◽  
Acoustic Instability ◽  
Anisotropic Viscosity

ABSTRACT Weakly collisional, magnetized plasmas characterized by anisotropic viscosity and conduction are ubiquitous in galaxies, haloes, and the intracluster medium (ICM). Cosmic rays (CRs) play an important role in these environments as well, by providing additional pressure and heating to the thermal plasma. We carry out a linear stability analysis of weakly collisional plasmas with CRs using Braginskii MHD for the thermal gas. We assume that the CRs stream at the Alfvén speed, which in a weakly collisional plasma depends on the pressure anisotropy (Δp) of the thermal plasma. We find that this Δp dependence introduces a phase shift between the CR-pressure and gas-density fluctuations. This drives a fast-growing acoustic instability: CRs offset the damping of acoustic waves by anisotropic viscosity and give rise to wave growth when the ratio of CR pressure to gas pressure is ≳αβ−1/2, where β is the ratio of thermal to magnetic pressure, and α, typically ≲1, depends on other dimensionless parameters. In high-β environments like the ICM, this condition is satisfied for small CR pressures. We speculate that the instability studied here may contribute to the scattering of high-energy CRs and to the excitation of sound waves in galaxy-halo, group and cluster plasmas, including the long-wavelength X-ray fluctuations in Chandra observations of the Perseus cluster. It may also be important in the vicinity of shocks in dilute plasmas (e.g. cluster virial shocks or galactic wind termination shocks), where the CR pressure is locally enhanced.

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