1,928 research outputs found
Galactic synchrotron emission with cosmic ray propagation models
Cosmic-ray (CR) leptons produce radio synchrotron radiation by gyrating in
interstellar magnetic fields (B-field). Details of B-fields, CR electron
distributions and propagation are still uncertain. We present developments in
our modelling of Galactic radio emission with the GALPROP code. It now includes
calculations of radio polarization, absorption, and free-free emission. Total
and polarized synchrotron emission are investigated in the context of physical
model of CR propagation. Predictions are compared with radio data from 22 MHz
to 2.3 GHz, and Wilkinson Microwave Anisotropy Probe data at 23 GHz. Spatial
and spectral effects on the synchrotron modelling with different CR
distribution, propagation halo size and CR propagation models are presented. We
find that all-sky total intensity and polarization maps are reasonably
reproduced by including an anisotropic B-field, with comparable intensity to
the regular one defined by rotation measures. A halo size of 10 kpc, which is
larger than usually assumed, is favoured. This work provides a basis for
further studies on foreground emission with the Planck satellite and on
interstellar gamma-ray emission with Fermi-Large Area Telescope.Comment: 19 pages, 15 figures, 2 tables. Published in MNRAS. Minor changes to
reflect the published versio
A New Determination Of The Diffuse Galactic and Extragalactic Gamma-Ray Emission
The GALPROP model for cosmic-ray propagation is able to make explicit
predictions for the distribution of galactic diffuse gamma-rays. We compare
different propagation models with gamma-ray spectra measured by EGRET for
various regions of the sky. This allows sensitive tests of alternative
explanations for the apparent excess emission observed at GeV gamma-rays. We
find that a population of hard-spectrum gamma-ray sources cannot be solely
responsible for the excess since it also appears at high latitudes; on the
other hand a hard cosmic-ray electron spectrum cannot explain the gamma-ray
excess in the inner Galaxy. By normalizing the cosmic ray spectra within
reasonable bounds under preservation of their shape we are able to obtain our
best prediction of the Galactic component of diffuse gamma rays, and show that
away from the Galactic plane it gives an accurate prediction of the observed
gamma-ray intensities. On this basis we reevaluate the extragalactic gamma-ray
background. We find that for some energies previous work underestimated the
Galactic contribution and hence overestimated the background. The new EGRB
spectrum shows a positive curvature similar to that expected for models of the
extragalactic gamma-ray emission based on contributions from unresolved
blazars.Comment: 6 pages, 3 figures, 1 tabl
Culture and concept design : a study of international teams
This paper explores the relationship between culture and performance in concept design. Economic globalisation has meant that the management of global teams has become of strategic importance in product development. Cultural diversity is a key factor in such teams, and this work seeks to better understand the effect this can have on two key aspects of the concept design process: concept generation and concept selection. To this end, a group of 32 students from 17 countries all over the world were divided into culturally diverse teams and asked to perform a short design exercise. A version of the Gallery Method allowed two kinds of activity to be monitored – the individual development of concepts and the collective filtering and selection of them. The effect of culture on these processes was the focus of the work. Using Hofstede’s cultural dimensions, the output from the sessions were reviewed according to national boundaries. The results indicate that individualism and masculinity had the most discernable effect on concept generation and concept selection respectively
Propagation in 3D spiral-arm cosmic-ray source distribution models and secondary particle production using PICARD
We study the impact of possible spiral-arm distributions of Galactic
cosmic-ray sources on the flux of various cosmic-ray nuclei throughout our
Galaxy. We investigate model cosmic-ray spectra at the nominal position of the
sun and at different positions within the Galaxy. The modelling is performed
using the recently introduced numerical cosmic ray propagation code
\textsc{Picard}. Assuming non-axisymmetric cosmic ray source distributions
yields new insights on the behaviour of primary versus secondary nuclei.
We find that primary cosmic rays are more strongly confined to the vicinity
of the sources, while the distribution of secondary cosmic rays is much more
homogeneous compared to the primaries. This leads to stronger spatial variation
in secondary to primary ratios when compared to axisymmetric source
distribution models. A good fit to the cosmic-ray data at Earth can be
accomplished in different spiral-arm models, although leading to decisively
different spatial distributions of the cosmic-ray flux. This results in very
different cosmic ray anisotropies, where even a good fit to the data becomes
possible. Consequently, we advocate directions to seek best fit propagation
parameters that take into account the higher complexity introduced by the
spiral-arm structure on the cosmic-ray distribution. We specifically
investigate whether the flux at Earth is representative for a large fraction of
the Galaxy. The variance among possible spiral-arm models allows us to quantify
the spatial variation of the cosmic-ray flux within the Galaxy in presence of
non-axisymmetric source distributions.Comment: 38 pages, 16 figures, accepted for publication in Astroparticle
Physic
Solar gamma rays and modulation of cosmic rays in the inner heliosphere
The first evidence of the gamma-ray emission from the quiescent Sun was found
in the archival EGRET data that was later confirmed by Fermi-LAT observations
with high significance. This emission is produced by Galactic cosmic rays (CRs)
penetrating the inner heliosphere and inter- acting with the solar atmosphere
and optical photons. The solar emission is characterized by two spatially and
spectrally distinct components: (i) disk emission due to the CR cascades in the
solar atmosphere, and (ii) spatially extended inverse Compton (IC) emission due
to the CR electrons scattering off of solar photons. The intensity of both
components associated with Galactic CRs anti-correlate with the level of the
solar activity being the brightest during solar minimum. In this paper we
discuss updates of the models of the IC component of the emission based on CR
measurements made at different levels of solar activity, and we make
predictions for e- ASTROGAM and AMEGO, proposed low-energy gamma-ray missions.Comment: 7 pages, 3 figures, Proceedings of the 35th International Cosmic Ray
Conference, ICRC201
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