21 research outputs found
Cosmic-ray transport in the heliosphere with HelioProp
Before being detected at Earth, charged cosmic rays propagate across the
Solar System and undergo interactions with the turbulent solar wind and with
the heliospheric magnetic field. As a result, they are subject to a series of
processes that include diffusion, convection, energy losses and drifts, which
significantly affect the shape and the intensity of the cosmic-ray fluxes at
low energies. Here we illustrate how all these mechanisms can be realistically
modelled with HelioProp, our public tool designed to treat cosmic-ray transport
through the heliosphere in a charge-dependent way. We present a detailed
description of the features of the code and we illustrate in a quantitative way
the effects that the propagation in the heliosphere can have on the different
cosmic-ray species with a particular emphasis on the antiparticle channels
relevant for dark matter indirect detection.Comment: 8 pages, 2 figures. Proceedings of the 35th International Cosmic Ray
Conference (ICRC 2017), Bexco, Busan, Kore
Breaks in interstellar spectra of positrons and electrons derived from time-dependent AMS data
Until fairly recently, it was widely accepted that local cosmic ray spectra
were largely featureless power laws, containing limited information on their
acceleration and transport. This viewpoint is currently being revised in the
light of evidence for a variety of spectral breaks in the fluxes of cosmic ray
nuclei. Here, we focus on cosmic ray electrons and positrons which at the
highest energies must be of local origin due to strong radiative losses. We
consider a pure diffusion model for their Galactic transport and determine its
free parameters by fitting data in a wide energy range: measurements of the
interstellar spectrum by Voyager at MeV energies, radio synchrotron data
(sensitive to GeV electrons and positrons) and local observations by AMS up to
~ 1 TeV. For the first time, we also model the time-dependent fluxes of cosmic
ray electrons and positrons at GeV energies recently presented by AMS, treating
solar modulation in a simple extension of the widely used force-field
approximation. We are able to reproduce all the available measurements to date.
Our model of the interstellar spectrum of cosmic ray electrons and positrons
requires the presence of a number of spectral breaks, both in the source
spectra and the diffusion coefficients. While we remain agnostic as to the
origin of these spectral breaks, their presence will inform future models of
the microphysics of cosmic ray acceleration and transport.Comment: 19 pages, 9 figures; submitted to PR
AMS-02 electrons and positrons: astrophysical interpretation and Dark Matter constraints
We present here a quantitative analysis of the recent AMS-02 data with the purpose of investigating the interplay between astrophysical sources and Dark Matter in their interpretation. First, we show that AMS-02 leptonic measurements are in a remarkably good agreement with the hypothesis that all electrons and positrons are the outcome of primary or secondary astrophysical processes. Then, we add Dark Matter to the picture, in order to establish which are the informations on its annihilation cross section (or lifetime) that can be inferred by fitting AMS-02 data within a scenario in which Dark Matter and astrophysical sources jointly contribute to the different leptonic observables. In particular, by performing a Markov Chain Monte Carlo sampling of the parameters space of the theory, we attempt at characterizing the significance of a possible Dark Matter contribution to the observed data and we derive robust upper limits on the Dark Matter annihilation/decay rate
Cosmic-ray propagation with DRAGON2: II. Nuclear interactions with the interstellar gas
Understanding the isotopic composition of cosmic rays (CRs) observed near
Earth represents a milestone towards the identification of their origin. Local
fluxes contain all the known stable and long-lived isotopes, reflecting the
complex history of primaries and secondaries as they traverse the interstellar
medium. For that reason, a numerical code which aims at describing the CR
transport in the Galaxy must unavoidably rely on accurate modelling of the
production of secondary particles. In this work we provide a detailed
description of the nuclear cross sections and decay network as implemented in
the forthcoming release of the galactic propagation code DRAGON2. We present
the secondary production models implemented in the code and we apply the
different prescriptions to compute quantities of interest to interpret local CR
fluxes (e.g., nuclear fragmentation timescales, secondary and tertiary source
terms). In particular, we develop a nuclear secondary production model aimed at
accurately computing the light secondary fluxes (namely: Li, Be, B) above 1
GeV/n. This result is achieved by fitting existing empirical or semi-empirical
formalisms to a large sample of measurements in the energy range 100 MeV/n to
100 GeV/n and by considering the contribution of the most relevant decaying
isotopes up to iron. Concerning secondary antiparticles (positrons and
antiprotons), we describe a collection of models taken from the literature, and
provide a detailed quantitative comparison.Comment: 22 pages, 12 figure
DRAGON2: new features on energy losses treatment
In recent years we witnessed several experiments measuring a large set of observables related
to Cosmic-ray physics with an unprecedented level of precision. In order to be able to fully
exploit this great amount of new data we must act to refine our theoretical predictions. This
can be achieved by building more realistic models of Cosmic-ray Galactic transport. The
DRAGON project has been pursued in order to model Cosmic-rays propagation under realistic
conditions and to allow a comparison with a wide set of experimental data. Studies brought forth
with DRAGON showed how a treatment of Cosmic rays energy losses as realistic as possible is
pivotal. In DRAGON2, the new version of the code, a more accurate, second order scheme for
Cosmic Rays energy losses is implemented. In addition, the new version of the code allows us
to investigate the impact of different models for Interstellar Radiation Field or galactic magnetic
field. We present comparison between the previous energy losses approach and the new one, as
well as validation test by comparing our numerical results with a set of analytical solutions. We
study in particular the interplay of diffusion, reacceleration, and energy losses in a realistic case,
and their impact on leptonic spectrum