Lifetime Of Cosmic Rays Research Articles

FOSSIL IMPRINT OF A POWERFUL FLARE AT THE GALACTIC CENTER ALONG THE MAGELLANIC STREAM

The Fermi satellite discovery of the gamma-ray emitting bubbles extending 50 deg (10 kpc) from the Galactic Centre has revitalized earlier claims that our Galaxy has undergone an explosive episode in the recent past. We now explore a new constraint on such activity. The Magellanic Stream is a clumpy gaseous structure passing over the South Galactic Pole (SGP) at a distance of at least 50-100 kpc. Patchy H-alpha emission discovered along the Magellanic Stream over the SGP is a factor of 5 too bright to have been produced by the Galactic stellar population. Time-dependent models of Stream clouds exposed to a flare in ionising photon flux show that the ionised gas must recombine and cool for a time interval 0.6 - 2.9 Myr for the emitted H-alpha surface brightness to drop to the observed level. A nuclear starburst is ruled out. Sgr A* is a more likely candidate because it is two orders of magnitude more efficient at converting gas to UV radiation. The central black hole (4 x 10^6 Msun) can supply the required ionising luminosity with a fraction of the Eddington accretion rate (3-30%). In support of nuclear activity, the H-alpha emission along the Stream has a polar angle dependence peaking close to the SGP. Moreover, it is now generally accepted that the Stream over the SGP must be further than the Magellanic Clouds. At the lower halo gas densities, shocks become too ineffective and are unlikely to give rise to a polar angle dependence in the H-alpha emission. Thus it is likely that the Stream emission arose from a `Seyfert flare' that was active 1-3 Myr ago, consistent with the cosmic ray lifetime in the Fermi bubbles. Sgr A* activity today is greatly suppressed (70-80 dB) relative to the Seyfert outburst...

SOME ASPECTS OF THE PROPAGATION OF SUPER-HIGH ENERGETIC COSMIC RAYS IN THE GALAXY

The origin of the knee in the energy spectrum of cosmic rays is one of the central questions of high-energy astrophysics. One possible explanation is the energy dependent leakage of nuclei from the Galaxy due to their propagation. The latter is investigated in a combined method using numerical calculations of trajectories and the diffusion approximation. The life time of cosmic rays in the Galaxy and the corresponding pathlength are presented. The resulting energy spectra as observed at Earth are discussed and compared to experimental data.

Formation of the cosmic-ray spectrum due to its propagation in the Galaxy

A model of cosmic ray propagation is proposed to explain the knee of the cosmic ray energy spectrum in the energy range E ∼ 10 14 −10 17 eV. The numerous stellar winds (SW), ionized hydrogen regions (H-II) and supernova remnants (SNR) in the Galaxy are taken into account in this model. The gas density and the magnetic field in these regions are different from the interstellar gas density and the interstellar magnetic field. Therefore they act as scattering centres and magnetic traps for cosmic rays. It is shown that these regions influence cosmic ray propagation in the Galaxy. Our results show that the collision time between cosmic rays and the SNR, SW, and H-II regions is much less than the cosmic ray lifetime in standard models (Berezinskii et al. 1984; Ginzburg & Syrovatskii 1963), in which only the nuclear interaction of the particles with interstellar gas is taken into account. Cosmic ray energies, and thus the cosmic ray spectrum, change due to interactions with these regions. Cosmic ray energy losses in these regions due to adiabatic cooling are comparable to the losses due to nuclear interaction with interstellar gas. It is therefore necessary to take these into account in galactic cosmic ray propagation models.

Measurement of the Isotopic Composition of Cosmic‐Ray Helium, Lithium, Beryllium, and Boron up to 1700 MeV per Atomic Mass Unit

We present data from the second flight of the superconducting magnet instrument for light isotopes (SMILI), which took place on 1991 July 24. This instrument was optimized to determine the isotopic composition of He, Li, Be, and B in the Galactic cosmic rays, up to an energy of 2 GeV amu-1. The abundances of He, Li, and B are found to be consistent with standard models of cosmic-ray propagation. Our measurement of the abundances of the beryllium isotopes suggests an enhancement of the fraction of the isotope 10Be over that found at low energy. Of 26 beryllium events, nine are found to be 10Be. Monte Carlo calculations based on this observation imply the mean lifetime of cosmic rays to be less than 6 Myr at the 97.5% confidence level.

The isotopic composition of cosmic-ray beryllium and its implication for the cosmic ray's age

We report a new measurement of the cosmic-ray isotopic composition of beryllium in the low-energy range from 35 to 113 MeV per nucleon. This measurement was made using the High Energy Telescope of the CRS experiment on the Voyager 1 and 2 spacecraft during the time period from 1977 to 1991. In this overall time period of 14 years the average solar modulation level was about 500 MV. The cosmic-ray beryllium isotopes were completely separated with an average mass resolution sigma of 0.185 amu. The isotope fractions of Be-7, Be-9, and Be-10 obtained are 52.4 +/- 2.9%, 43.3 +/- 3.7%, and 4.3 +/- 1.5%, respectively. The measured cosmic-ray abundances of Be-7 and Be-9 are found to be in agreement with calculations based on standard Leaky-Box model for the interstellar propagation of cosmic-ray nuclei using the recent cross sections of the New Mexico-Saclay collaboration. From our observed ratio Be-10/Be = 4.3 +/- 1.5% we deduce an average interstellar density of about 0.28 (+0.14, -0.11) atoms/cu cm, and a cosmic-ray lifetime for escape of 27 (+19, -9) x 10<SUP>6</SUP> years. The surviving fraction of Be-10 is found to be 0.19 +/- 0.07. Modifications to the conclusions of the Leaky-Box model when a diffusion + convection halo model for propagation is used are also considered.

Cosmic-ray lifetime in the galaxy: Experimental results and models

The containment lifetime of the cosmic radiation is a crucial parameter in the investigation of the cosmic-ray origin and plays an important role in the dynamics of the Galaxy. The separation of the cosmic-ray Be isotopes achieved by two satellite experiments is considered in this paper, and from the measured isotopic ratio between the radioactive 10Be (half-life = 1.5 × 106 yr) and the stable 9Be, it is deduced that the cosmic rays propagate through matter with an average density of 0.24 ± 0.07 atoms cm-3, lower than the traditionally quoted average density in the galactic disk of 1 atom cm-3. This paper reviews the implications of this result for the cosmic-ray age mainly in the context of two models of confinement and propagation: the homogeneous model, normally identified with confinement to the galactic gaseous disk, and a diffusion model in which the cosmic rays extend into a galactic halo. The propagation calculations use: The satellite results and their implications are compared with the information on the cosmic-ray age derived from other cosmic-ray radioactive nuclei and the measured differential energy spectrum of high-energy electrons. It is a major conclusion of this paper that in a homogeneous model the cosmic-ray age is 15(+7, -4) million years, i.e., about a factor 4 longer than early estimates based on the abundances of the light nuclei Li, Be, and B and a nominal interstellar density of 1 atom cm -3. The lifetime is even longer when the satellite results are applied to a diffusion halo model. The deduced traversed matter density, together with other astrophysical considerations, suggest the population of a galactic halo by the cosmic rays.

Distributed reacceleration of cosmic rays.

We develop a model in which cosmic rays, in addition to their initial acceleration by a strong shock, are continuously reaccelerated (e.g., by weak shocks) while propagating through the galaxy. The equations describing this acceleration scheme are solved analytically (approximating ionization losses by a cutoff) and numerically. Solutions for the spectra of primary and secondary cosmic rays are given in a closed analytic form, and they allow a rapid search in parameter space for viable propagation models with distributed reacceleration included. The observed boron-to-carbon ratio can be reproduced by the reacceleration theory over a range of escape parameters, some of them quite different from the standard "leaky box" model. It is also shown that even a very modest amount of reacceleration by strong shocks causes the boron-to carbon ratio to level off at sufficiently high energies, and this effect may be observed in the CRNE data. Several other curiosities in the data may be explained naturally if a modest amount of distributed reacceleration is invoked, including (a) the apparent truncation at low energy in the otherwise exponential pathlength distribution associated with the leaky box model, (b) the sub-iron isotopic anomalies and other effects noted by Silberberg et al., and (c) the discrepancy between the reported 10Be lifetime and the lifetime of cosmic rays in the dense strata of the galactic disk.

The age of the galactic cosmic rays derived from the abundance of Be-10

Satellite measurements of the abundance of the Be-10 isotope in galactic cosmic rays are used to determine the cosmic-ray lifetime for escape. The data are analyzed by employing a technique based on an extensive calibration of a cosmic-ray telescope with the aid of high-energy Be beams accelerated in a bevatron. It is found that the Be-10/Be abundance ratio at 80 MeV/nucleon is 0.028 + or - 0.104. A comparison of this result with calculations based on a homogeneous steady-state model of galactic cosmic-ray confinement and propagation yields an average interstellar density of 0.18 (+0.18, -0.11) atom/cu cm and a corresponding cosmic-ray lifetime of 17 (+24, -8) million years after solar modulation is taken into account. The low average density traversed by the cosmic rays is shown to suggest that the particles may be spending the major part of their existence in regions of very low matter density. The consequences of these results are discussed for models of cosmic-ray propagation in the Galaxy, including such alternatives as propagation in a galactic halo or in regions of interstellar space where the interstellar gas density is very low.

High-Energy Cosmic-Ray Electrons: A New Measurement Using Transition-Radiation Detectors

A new detector for cosmic-ray electrons, consisting of a combination of a transition-radiation detector and a shower detector, has been constructed, calibrated at accelerator beams, and exposed in a balloon flight under 5 g/sq cm of atmosphere. The design of this instrument and the methods of data analysis are described. Preliminary results in the energy range 9-300 GeV are presented. The energy spectrum of electrons is found to be significantly steeper than that of protons, consistent with a long escape lifetime of cosmic rays in the galaxy.

Consequences of a lifetime greater than 10 to the 7th power years for galactic cosmic rays

view Abstract Citations (87) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Consequences of a lifetime greater than 107 years for galactic cosmic rays. Jokipii, J. R. Abstract The implications of recent determinations of the cosmic-ray lifetime are discussed. It is concluded that the observations are consistent with a 'dynamical halo' model in which cosmic rays are confined in an outward-moving galactic halo by self-generated hydromagnetic waves. Alternative models which do not incorporate a halo, but which have the cosmic rays propagate in regions of reduced density in the galactic disk, are also briefly discussed. Publication: The Astrophysical Journal Pub Date: September 1976 DOI: 10.1086/154678 Bibcode: 1976ApJ...208..900J Keywords: Astronomical Models; Cosmic Rays; Galactic Radiation; Magnetohydrodynamic Waves; Radiative Lifetime; Disks (Shapes); Galactic Structure; Halos; Particle Flux Density; Spiral Galaxies; Space Radiation full text sources ADS |

Cosmic rays and interstellar tunnels

MEASUREMENTS have been made1 of the isotopic abundances of Be in cosmic rays, which have led to the conclusion that the typical cosmic ray lifetime in the galaxy is ∼ 2× 107 yr. Furthermore, measurements2 of the cosmic ray electron energy spectrum in the range 6–100 GeV, have shown a bend in the spectrum which can be attributed to inverse Compton and synchrotron losses. The position of the bend is indicative of the cosmic ray electron lifetime, and an age of 1.2×107 yr is derived.

The relative abundance of the isotopes of Li, Be and B and the age of cosmic rays

Using a balloon borne double dE/dx x total energy telescope we have determined the isotopic composition of cosmic ray Li, Be and B nuclei in the energy range 100–250 MeV nuc.−1. The measured mass resolution, σ for these nuclei is ∼0.3 AMU. The observed isotopic composition is in agreement with that predicted on the basis of interstellar fragmentation with the exception of a deficiency of Be10. If the low abundance of Be10 is attributed to the decay of this radioactive isotope we obtain a mean cosmic ray lifetime of (3.4 −1.3 +3.4 )×106 yr.

Cosmic-Ray Evolution due to Interactions with Self-Excited Plasma Waves

view Abstract Citations (12) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cosmic-Ray Evolution due to Interactions with Self-Excited Plasma Waves Lee, Martin A. Abstract We use kinetic equations describing a relativistic plasma embedded in a uniform ambient magnetic field to investigate the time evolution of the cosmic-ray momentum distribution due to interactions between the cosmic-ray particles and their self-excited waves. Within the cosmic-ray lifetime there is negligible change in the cosmic-ray energy spectrum, but for particles with energy less than about 20 0eV there occurs a marked reduction of the cosmic-ray streaming velocity to a value of the order of, but greater than, the AlIven speed, the exact value depending sensitively on the timescale for ion-neutral collisions. Publication: The Astrophysical Journal Pub Date: December 1972 DOI: 10.1086/151838 Bibcode: 1972ApJ...178..837L full text sources ADS |

Adiabatic Propagation of Cosmic Rays in the Galaxy

view Abstract Citations (7) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Adiabatic Propagation of Cosmic Rays in the Galaxy Barrowes, Steven C. Abstract An analysis is presented for the propagation of charged cosmic rays away from a source in a relatively smooth galactic magnetic field. Tbe expected intensity of the resulting narrow-angle anisotropy is related to the particle flux produced by the source. The probable number of such anisotropies is derived, based on the lifetime of cosmic rays and the number of sources in the Galaxy. The agreement with experimental evidence and future possibilities of the model are discussed. Publication: The Astrophysical Journal Pub Date: October 1972 DOI: 10.1086/151685 Bibcode: 1972ApJ...177...45B full text sources ADS |

Cosmic-ray lifetime and high-energy γ-rays from the galaxy

Cosmic-ray lifetime and high-energy γ-rays from the galaxy

Considerations affecting the estimation of cosmic-ray age

Previous investigations by Daniel and Durgaprasad on the ratios Be/B and Be/Li in the primary cosmic radiation exploited the decay of 10Be produced in space to deduce a confinement time for cosmic rays in the galaxy. They concluded that this "age" T is at least 50 million years, and thence inferred that the cosmic-ray nuclei are trapped in a volume much larger than that of the galactic disk. These conclusions depended upon the values of fragmentation cross sections available in 1962 to Badhwar, Daniel, and Vijayalakshmi. Recent values of the Orsay group, however, reduce the calculated rates of 10Be and 9Be production by an order of magnitude; and an analysis based upon the latest cross sections leads to the following conclusions: (1) The possibility that cosmic rays are mainly confined to the disk of the galaxy and that T ≈ 106 years is not excluded. (2) The fragmentation parameter for medium nuclei [Formula: see text] into light nuclei [Formula: see text] is revised from 0.48 (the value of Badhwar et al.) to 0.34. (3) The mean path-length of 2.5 ± 0.5 g/cm2 of Badhwar et al. is revised to 4 ± 1 g/cm2. (4) 7Be now appears to be the principal component of cosmic-ray beryllium (about 70 or 80%, depending upon the cosmic-ray lifetime).

Evolution of Cosmic Rays in Galaxies

The relative intensity of cosmic ray sources in external galaxies of different types is estimated from the relative frequency of supernovae there. Also the cosmic ray energy in normal galaxies is estimated from radio astronomical data. It is found that the intensity and the lifetime of cosmic rays in spiral galaxies are nearly constant during their evolutional stage as spirals.

PRESENT STATUS OF THE QUESTION OF THE ORIGIN OF COSMIC RAYS

Introduction 504 1. Primary Cosmic Rays Near the Earth 505 a) Chemical Composition 505 b) Energy Spectrum 506 2. Radio-Astronomical Data 509 a) Magnetic Bremsstrahlung (Synchrotron Radiation) 509 b) Certain Results of Observations and their Interpretation (Structure of the Galaxy, Discrete Sources) 510 3. Lifetime of Cosmic Rays and the Character of their Motion in the Galaxy and in the Metagalaxy 515 a) Nuclear Lifetime of Cosmic Rays 515 b) The Role of Cosmic Rays Produced at an Earlier Stage of Evolution of the Galaxy 517 c) Character of Motion and Escape of Cosmic Rays from the Galaxy 518 d) Cosmic Rays of Metagalactic Origin 520 4. Sources of Cosmic Rays. Mechanism of Acceleration and Chemical Composition of Cosmic Rays 524 a) Sources of Cosmic Rays 524 b) Mechanisms of Acceleration and Energy Spectrum of Cosmic Rays. Possibility of Preferred Acceleration of Heavy Nuclei 526 c) Transformation of Chemical Composition of Cosmic Rays in the Interstellar Medium. 531 d) Discussion of the Chemical Composition of Cosmic Rays 533 Concluding Remarks 536 Literature 538

Supernova Origin of Cosmic Rays

The supernova origin of cosmic rays is proposed in connection with the stellar evolution and the building up of heavy elements in the core of stars as they evolve. Nearly equal abundances of heavy and medium nuclei in primary cosmic rays suggest that the sources may be such stars, in which the thermonuclear reactions of building up heavy elements take place and which eventually explode as supernovae. The light elements, Li, Be and B, in galactic matter are considered to be generated by the nuclear bombardment of heavier nuclei at the explosion. The number of cosmic ray particles injected there is estimated in reference to the radio emission of supernova remnants. If the number injected is of the order of 1051 per supernova and the explosion is more frequent than now observed, the supernova origin is shown to be not inconsistent with cosmic ray as well as astronomical evidences. The galactic model suitable to our interpretation is a sphere with magnetic clouds. The life time of cosmic rays in this galaxy is estimated to be of the order of 108 years, corresponding to the fact that the mean thickness of interstellar matter traversed by cosmic rays is about 1 g cm-2, that is, estimated from the abundance of the light nuclei in the primary cosmic rays.

Production of Cosmic Radiation at the Sun

A calculation is made of the average production rate of 4-Bv cosmic-ray particles at the sun. The calculation is based upon the recent experimental evidence that the frequently occurring small solar flares produce temporary increases of neutron intensity in suitably located neutron pile detectors. This production rate, averaged over the 11-year solar cycle, is somewhat in excess of the absorption rate of 4-Bv particles by bodies in the solar system. If the production at the sun is to account for most of the observed cosmic radiation intensity, a trapping magnetic field is required. Limits on the size of such a trapping volume are estimated by considering the limits of cosmic-ray lifetime; the requirement of a high degree of radiation isotropy at the earth is satisfied. The existence of high-energy particles in the cosmic radiation imposes the principal difficulty for any solar origin hypothesis.