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Register a new userGALPROP cosmic-ray propagation code: recent results and updates
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Information on cosmic-ray (CR) composition comes from direct CR measurements while their distribution in the Galaxy is evaluated from observations of their associated diffuse emission in the range from radio to gamma rays. Even though the main interaction processes are identified, more and more precise observations provide an opportunity to study more subtle effects and pose a challenge to the propagation models. GALPROP is a sophisticated CR propagation code that is being developed for about 20 years. It provides a unified framework for interpretations of data from many different types of experiments. It is used for a description of direct CR measurements and associated interstellar emissions (radio to gamma rays), thereby providing important information about CR injection and propagation in the interstellar medium. By accounting for all relevant observables at a time, the GALPROP code brings together theoretical predictions, interpretation of the most recent observations, and helps to reveal the signatures of new phenomena. In this paper we review latest applications of GALPROP and address ongoing and near future improvements. We are discussing effects of different propagation models, and of the transition from cylindrically symmetrical models to a proper 3D description of the components of the interstellar medium and the source distribution.
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Some recent extensions to the GALPROP cosmic-ray propagation package are described. The enhancements include: an accurate solution option, improved convection formulation, alternative spatial boundary conditions, polarized synchrotron emission, new magnetic field models, updated gamma-ray production cross-sections, free-free radio emission and absorption, primary positrons, additional injection spectral breaks, deuterium production by pp fusion, hadronic energy losses, improved HEALPix skymap format, compatibility with latest HEALPix release, and various bug fixes. The Explanatory Supplement has been extensively updated, including details of these enhancements. A compatible plot package GALPLOT for GALPROP output is also provided, as well as other related software.
The last decade has been dense with new developments in the search for the sources of Galactic cosmic rays. Some of these developments have confirmed the tight connection between cosmic rays and supernovae in our Galaxy, through the detection of gamma rays and the observation of thin non-thermal X-ray rims in supernova remnants. Some other, such as the detection of features in the spectra of some chemicals opened new questions on the propagation of cosmic rays in the Galaxy and on details of the acceleration process. Here I will summarize some of these developments and their implications for our understanding of the origin of cosmic rays. I will also discuss some new avenues that are being pursued in testing the supernova origin of Galactic cosmic rays.
The High Altitude Water Cherenkov (HAWC) telescope recently observed extended emission around the Geminga and PSR~B0656+14 pulsar wind nebulae (PWNe). These observations have been used to estimate cosmic-ray (CR) diffusion coefficients near the PWNe that appear to be more than two orders of magnitude smaller than that typically derived for the interstellar medium from the measured abundances of secondary species in CRs. Two-zone diffusion models have been proposed as a solution to this discrepancy, where the slower diffusion zone (SDZ) is confined to a small region around the PWN. Such models are shown to successfully reproduce the HAWC observations of the Geminga PWN while retaining consistency with other CR data. It is found that the size of the SDZ influences the predicted positron flux and the spectral shape of the extended $gamma$-ray emission at lower energies that can be observed with the {it Fermi} Large Area Telescope ({it Fermi} LAT). If the two observed PWNe are not unique, then it is likely that there are similar pockets of slow diffusion around many CR sources elsewhere in the Milky Way. The consequences of such picture for Galactic CR propagation is explored.
LOPES is a digital antenna array at the Karlsruhe Institute of Technology, Germany, for cosmic-ray air-shower measurements. Triggered by the co-located KASCADE-Grande air-shower array, LOPES detects the radio emission of air showers via digital radio interferometry. We summarize the status of LOPES and recent results. In particular, we present an update on the reconstruction of the primary-particle properties based on almost 500 events above 100 PeV. With LOPES, the arrival direction can be reconstructed with a precision of at least 0.65{deg}, and the energy with a precision of at least 20 %, which, however, does not include systematic uncertainties on the absolute energy scale. For many particle and astrophysics questions the reconstruction of the atmospheric depth of the shower maximum, Xmax, is important, since it yields information on the type of the primary particle and its interaction with the atmosphere. Recently, we found experimental evidence that the slope of the radio lateral distribution is indeed sensitive to the longitudinal development of the air shower, but unfortunately, the Xmax precision at LOPES is limited by the high level of anthropogenic radio background. Nevertheless, the developed methods can be transferred to next generation experiments with lower background, which should provide an Xmax precision competitive to other detection technologies.
I summarize in this paper the results and perspectives of representative ground experiments for the observation of very high energy cosmic rays.
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