218 research outputs found
Time and Charge-Sign Dependence of the Heliospheric Modulation of Cosmic Rays
Simultaneous and continuous observations of galactic cosmic-ray electrons and
positrons from the PAMELA and AMS02 space experiments are most suitable for
numerical modeling studies of the heliospheric modulation of these particles
below 50 GeV. A well-established comprehensive three-dimensional modulation
model is applied to compute full spectra for electrons and positrons with the
purpose of reproducing the observed ratio positrons/electrons for a period
which covers the previous long and unusual deep solar minimum activity and the
recent maximum activity phase including the polarity reversal of the solar
magnetic field. For this purpose the very local interstellar spectra for these
particles were established first. Our study is focused on how the main
modulation processes, including particle drifts, and other parameters such as
the three major diffusion coefficients, had evolved, and how the corresponding
charge-sign dependent modulation had occurred subsequently. The end result of
our effort is the detailed reproduction of positron/electrons from 2006 to
2015, displaying both qualitative and quantitative agreement with the main
observed features. Particularly, we determine how much particle drifts is
needed to explain the time dependence exhibited by the observed
positron/electron during each solar activity phase, especially during the
polarity reversal phase when no well-defined magnetic polarity was found.Comment: 16 pages, 8 figures, Submitted to Astrophysical Journa
Analysis on H Spectral Shape During the Early 2012 SEPs with the PAMELA Experiment
The satellite-borne PAMELA experiment has been continuously collecting data since 2006.This apparatus is designed to study charged particles in the cosmic radiation. The combination of a permanent magnet, a silicon strip tracker and a silicon-tungsten imaging calorimeter, and the redundancy of instrumentation allow very precise studies on the physics of cosmic rays in a wide energy range and with high statistics. This makes PAMELA a very suitable instrument for Solar Energetic Particle (SEP) observations. Not only does its pan the energy range between the ground-based neutron monitor data and the observations of SEPs from space,but PAMELA also carries out the first direct measurements of the composition for the highest energy SEP events, including those causing Ground Level Enhancements (GLEs).In particular, PAMELA has registered many SEP events during solar cycle 24,offering unique opportunities to address the question of high-energy SEP origin. A preliminary analysis on proton spectra behaviour during this event is presented in this work
Trapped proton fluxes at low Earth orbits measured by the PAMELA experiment
We report an accurate measurement of the geomagnetically trapped proton
fluxes for kinetic energy above > 70 MeV performed by the PAMELA mission at low
Earth orbits (350-610 km). Data were analyzed in the frame of the adiabatic
theory of charged particle motion in the geomagnetic field. Flux properties
were investigated in detail, providing a full characterization of the particle
radiation in the South Atlantic Anomaly region, including locations, energy
spectra and pitch angle distributions. PAMELA results significantly improve the
description of the Earth's radiation environment at low altitudes placing
important constraints on the trapping and interaction processes, and can be
used to validate current trapped particle radiation models.Comment: 22 pages, 5 figure
Time dependence of the e^- flux measured by PAMELA during the July 2006 - December 2009 solar minimum
Precision measurements of the electron component in the cosmic radiation
provide important information about the origin and propagation of cosmic rays
in the Galaxy not accessible from the study of the cosmic-ray nuclear
components due to their differing diffusion and energy-loss processes. However,
when measured near Earth, the effects of propagation and modulation of galactic
cosmic rays in the heliosphere, particularly significant for energies up to at
least 30 GeV, must be properly taken into account. In this paper the electron
(e^-) spectra measured by PAMELA down to 70 MeV from July 2006 to December 2009
over six-months time intervals are presented. Fluxes are compared with a
state-of-the-art three-dimensional model of solar modulation that reproduces
the observations remarkably well.Comment: 40 pages, 18 figures, 1 tabl
Search for anisotropies in cosmic-ray positrons detected by the PAMELA experiment
The PAMELA detector was launched on board of the Russian Resurs-DK1 satellite
on June 15, 2006. Data collected during the first four years have been used to
search for large-scale anisotropies in the arrival directions of cosmic-ray
positrons. The PAMELA experiment allows for a full sky investigation, with
sensitivity to global anisotropies in any angular window of the celestial
sphere. Data samples of positrons in the rigidity range 10 GV R
200 GV were analyzed. This article discusses the method and the results of the
search for possible local sources through analysis of anisotropy in positron
data compared to the proton background. The resulting distributions of arrival
directions are found to be isotropic. Starting from the angular power spectrum,
a dipole anisotropy upper limit \delta = 0.166 at 95% C.L. is determined.
Additional search is carried out around the Sun. No evidence of an excess
correlated with that direction was found.Comment: The value of the dipole anisotropy upper limit has been changed. The
method is correct but there was a miscalculation in the relative formul
Measurement of boron and carbon fluxes in cosmic rays with the PAMELA experiment
The propagation of cosmic rays inside our galaxy plays a fundamental role in
shaping their injection spectra into those observed at Earth. One of the best
tools to investigate this issue is the ratio of fluxes for secondary and
primary species. The boron-to-carbon (B/C) ratio, in particular, is a sensitive
probe to investigate propagation mechanisms. This paper presents new
measurements of the absolute fluxes of boron and carbon nuclei, as well as the
B/C ratio, from the PAMELA space experiment. The results span the range 0.44 -
129 GeV/n in kinetic energy for data taken in the period July 2006 - March
2008
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