62 research outputs found
Magnetospheric substorm effects on energetic electrons in the outer Van Allen belt /Summary of technical report CR-137/
Substorm-associated acceleration effects on electron increases in post-midnight sector of outer radiation bel
Experimental verification of drift shell splitting in the distorted magnetosphere
OGO-3 and ATS-1 data used in experimental verification of drift shell splitting in distorted magnetospher
The effects of discreteness of galactic cosmic rays sources
Most studies of GeV Galactic Cosmic Rays (GCR) nuclei assume a steady
state/continuous distribution for the sources of cosmic rays, but this
distribution is actually discrete in time and in space. The current progress in
our understanding of cosmic ray physics (acceleration, propagation), the
required consistency in explaining several GCRs manifestation (nuclei,
,...) as well as the precision of present and future space missions
(e.g. INTEGRAL, AMS, AGILE, GLAST) point towards the necessity to go beyond
this approximation. A steady state semi-analytical model that describes well
many nuclei data has been developed in the past years based on this
approximation, as well as others. We wish to extend it to a time dependent
version, including discrete sources. As a first step, the validity of several
approximations of the model we use are checked to validate the approach: i) the
effect of the radial variation of the interstellar gas density is inspected and
ii) the effect of a specific modeling for the galactic wind (linear vs
constant) is discussed. In a second step, the approximation of using continuous
sources in space is considered. This is completed by a study of time
discreteness through the time-dependent version of the propagation equation. A
new analytical solution of this equation for instantaneous point-like sources,
including the effect of escape, galactic wind and spallation, is presented.
Application of time and space discretness to definite propagation conditions
and realistic distributions of sources will be presented in a future paper.Comment: final version, 8 figures, accepted in ApJ. A misprint in fig 8 labels
has been correcte
Secondary Cosmic Ray Nuclei from Supernova Remnants and Constraints to the Propagation Parameters
The secondary-to-primary B/C ratio is widely used to study the cosmic ray
(CR) propagation processes in the Galaxy. It is usually assumed that secondary
nuclei such as Li-Be-B are entirely generated by collisions of heavier CR
nuclei with the interstellar medium (ISM). We study the CR propagation under a
scenario where secondary nuclei can also be produced or accelerated from
galactic sources. We consider the processes of hadronic interactions inside
supernova remnants (SNRs) and re-acceleration of background CRs in strong
shocks. Thus, we investigate their impact in the propagation parameter
determination within present and future data. The spectra of Li-Be-B nuclei
emitted from SNRs are harder than those due to CR collisions with the ISM. The
secondary-to-primary ratios flatten significantly at ~TeV/n energies, both from
spallation and re-acceleration in the sources. The two mechanisms are
complementary to each other and depend on the properties of the local ISM
around the expanding remnants. The secondary production in SNRs is significant
for dense background media, n ~1 cm^-3, while the amount of re-accelerated CRs
is relevant for SNRs expanding into rarefied media, n ~0.1 cm-3. Due to these
effects, the the diffusion parameter 'delta' may be misunderstood by a factor
of ~5-15%. Our estimations indicate that an experiment of the AMS-02 caliber
can constrain the key propagation parameters while breaking the
source-transport degeneracy, for a wide class of B/C-consistent models. Given
the precision of the data expected from on-going experiments, the SNR
production/acceleration of secondary nuclei should be considered, if any, to
prevent a possible mis-determination of the CR transport parameters.Comment: 13 pages, 9 figures; matches the published versio
Spatial Origin of Galactic Cosmic Rays in Diffusion Models: I- Standard sources in the Galactic disk
The propagation of Galactic Cosmic Ray nuclei having energies between 100
MeV/nuc and several PeV/nuc is strongly believed to be of diffusive nature. The
particles emitted by a source located in the disk do not pervade the whole
Galaxy, but are rather confined to a smaller region whose spatial extension is
related to the height of the diffusive halo, the Galactic wind and the
spallation rate. Following the pioneering work of Jones (1978), this paper
presents a general study on the spatial origin of cosmic rays, with a
particular attention to the role of spallations and Galactic wind. This
question is different, and to a certain extent disconnected, from that of the
origin of cosmic rays. We find the regions of the disk from which a given
fraction of cosmic rays detected in the Solar neighborhood were emitted
(f-surfaces). After a general study, we apply the results to a realistic source
distribution, with the propagation parameters obtained in our previous
systematic analysis of the observed secondary-to-primary ratios Maurin et al
(2002). The shape and size of these f-surfaces depend on the species as well as
on the values of the propagation parameters. For some of the models preferred
by our previous analysis (i.e. large diffusion slope ), these
f-surfaces are small and in some extreme cases only a fraction of a percent of
the whole Galactic sources actually contribute to the Solar neighborhood Cosmic
Ray flux. Moreover, a very small number of sources may be responsible for more
than 15 % of the flux detected in the Solar neighborhood. This may point
towards the necessity to go beyond the approximations of both homogeneity and
stationarity. Finally, the observed primary composition is dominated by sources
within a few kpc.Comment: revised version, 32 pages, to appear in A&A. Shortened version, with
corresction
Spallation dominated propagation of Heavy Cosmic Rays and the Local Interstellar Medium (LISM)
Measurements of ultra heavy nuclei at GeV/n energies in the galactic cosmic
radiation address the question of the sources (nucleosynthetic s- and
r-processes). As such, the determination of CR source abundances is a promising
way to discriminate between existing nucleosynthesis models. For primary
species (nuclei present and accelerated at sources), it is generally assumed
that the relative propagated abundances, if they are close in mass, are not too
different from their relative source abundances. Besides, the range of the
correction factor associated to propagation has been estimated in weighted slab
models only. Heavy CRs that are detected near Earth were accelerated from
regions that are closer to us than were the light nuclei. Hence, the geometry
of sources in the Solar neighbourhood, and as equally important, the geometry
of gas in the same region, must be taken into account. In this paper, a two
zone diffusion model is used, and as was previously investigated for
radioactive species, we report here on the impact of the local interstellar
medium (LISM) feature (under-dense medium over a scale ~100 pc) on primary and
secondary stable nuclei propagated abundances. Going down to Fe nuclei, the
connection between heavy and light abundances is also inspected. A general
trend is found that decreases the UHCR source abundances relative to the HCR
ones. This could have an impact on the level of r-process required to reproduce
the data.Comment: 12 pages, 9 figures, accepted by A&A. Comparison with truncated
weighted slab and discussion added. Figure 8 modified. New appendix on
truncated weighted slab techniqu
Diffusion coefficient and acceleration spectrum from direct measurements of charged cosmic ray nuclei
We discuss the potentials of several experimental configurations dedicated to
direct measurements of charged cosmic ray (CR) nuclei at energies \gsim 100
GeV/n. Within a two-zone propagation model for stable CRs, we calculate light
primary and secondary nuclei fluxes for different diffusion and acceleration
schemes. We show that the new detectors exploiting the long and ultra long
duration balloon flights could determine the diffusion coefficient power index
through the measurement of the boron-to-carbon ratio with an
uncertainty of about 10-15 %, if systematic errors are low enough. Only
space-based or satellite detectors will be able to determine with very
high accuracy even in the case of important systematic errors, thanks to the
higher energy reach and the less severe limitations in the exposure. We show
that no uncertainties other than those on affect the determination of
the acceleration slope , so that measures of light primary nuclei, such
as the carbon one, performed with the same experiments, will provide valuable
information on the acceleration mechanisms.Comment: 20 pages, 6 figs., Astropart. Physics, in pres
Entropy mapping of the outer electron radiation belt between the magnetotail and geosynchronous orbit
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94614/1/jgra21264.pd
- …