Nuclear physics. B, Proceedings, supplements最新文献

The role pulsar wind nebulae play in producing our locally observed cosmic ray spectrum remains murky, yet intriguing. Pulsar wind nebulae are born and evolve in conjunction with SNRs, which are favored sites of Galactic cosmic ray acceleration. As a result they frequently complicate interpretation of the gamma-ray emission seen from SNRs. However, pulsar wind nebulae may also contribute directly to the local cosmic ray spectrum, particularly the leptonic component. This paper reviews the current thinking on pulsar wind nebulae and their connection to cosmic ray production from an observational perspective. It also considers how both future technologies and new ways of analyzing existing data can help us to better address the relevant theoretical questions. A number of key points will be illustrated with recent results from the VHE (E > 100 GeV) gamma-ray observatory VERITAS.

The shape and composition of the primary spectrum of cosmic rays are key elements to understand the origin, acceleration and propagation of the Galactic cosmic rays. Besides the well known knee and ankle features, the recent results of KASCADE-Grande indicate that the measured energy spectrum exhibits also a less pronounced but still clear deviation from a single power law between the knee and the ankle, with a spectral hardening at 2 × 10¹⁶ eV and a steepening at 10¹⁷ eV. The average mass composition gets heavier after the knee till 10¹⁷ eV where a bending of the heavy component is observed. An indication of a hardening of the light component just above 10¹⁷ eV has been measured as well. In this paper the major results obtained so far by the KASCADE-Grande experiment are reviewed.

The Fermi Large Area Telescope (LAT) has observed Tycho Supernova Remnant in the MeV-GeV energy range. The spectrum has been studied using the first three years of data and new data are being collected. We present a multiwavelength model of the observed spectrum from radio to TeV energy range, based on the hypothesis of hadronic origin of γ-rays. As described by the Fermi acceleration theory, a single proton population was considered, modeled with a simple power-law in momentum. The photon emissivity is computed following Kamae et al (2006) [T. Kamae, et al., ApJ 647 (2006) 692]. The leptonic component is also taken into account according to Giordano et al. (2012) [F. Giordano, et al., ApJ 744 (2012) L2] prescriptions and it turns out to be negligible with respect to the hadronic one. The model returns a spectral index of $2.23(\pm 0.05)$ and an acceleration efficiency of 5% of the total kinetic energy expelled in Supernova explosion and it may provide a hint of the acceleration processes in SNRs up to energies close to the knee of cosmic ray spectrum. This work shows that experimental data can be easily explained with a simple model, representing a good test for the acceleration theory.

The ratios of heavy nuclei from Sulfur ($Z=16$) to Chromium ($Z=24$) fluxes to the flux of iron nuclei were measured recently in the ATIC-2 experiment. These ratios were the decreasing functions of energy from 5 GeV/n to approximately 50 GeV/n as expected. However, an unexpected sharp upturn in the ratios was observed at energy ∼ 50 GeV/n. In this paper, we revise the data and show that the statistical confidence of the observed upturn in the ATIC data is 99.7% and some additional arguments supporting the phenomenon are presented. A possible cause of the upturn is discussed and it is demonstrated that it can be partially understood within a model of ‘Closed Galaxy with Bubbles’ (CGB). Some features and problems of the CGB model are discussed.

The Extreme Universe Space Observatory (EUSO) onboard the Japanese Experiment Module (JEM-EUSO) of the International Space Station (ISS) is an innovative space-based mission with the aim of detecting Ultra-High Energy Cosmic Rays (UHECRs) from the ISS, by using the Earth's atmosphere as a calorimeter viewed by a fluorescence telescope. An observatory able to produce an arrival direction map with more than several hundreds events above 5 × 10¹⁹ eV would give important information on the origin of the UHECRs and identify structures in the sky map that contain information about the source density and/or distribution. This is likely to lead to an understanding of the acceleration mechanisms with a high potential for producing discoveries in astrophysics and/or fundamental physics. The scientific motivations of the mission as well as the current development status of the instrument and its performance are reviewed.

Fermi bubbles are giant gamma-ray structures extended north and south of the Galactic center with characteristic sizes of order of 10 kpc recently discovered by Fermi Large Area Telescope. Good correlation between radio and gamma-ray emission in the region covered by Fermi bubbles implies the presence of high-energy electrons in this region. Since it is relatively difficult for relativistic electrons of this energy to travel all the way from the Galactic sources toward Fermi bubbles one can assume that they accelerated in-situ. The corresponding acceleration mechanism should also affect the distribution of the relativistic protons in the Galaxy. Since protons have much larger lifetimes the effect may even be observed near the Earth. In our model we suggest that Fermi bubbles are created by acceleration of electrons on series of shocks born due to periodic star accretions by supermassive black hole Sgr A*. We propose that hadronic CR within the “knee” of the observed CR spectrum are produced by Galactic supernova remnants distributed in the Galactic disk. Reacceleration of these particles in the Fermi Bubble produces CRs beyond the knee. This model provides a natural explanation of the observed CR flux, spectral indexes, and matching of spectra at the knee.

A probable interpretation of the fine structure of all particle energy spectrum between the knee and the ankle (the sharp first knee at 3–4 PeV, the spectrum hardening at 20–30 PeV, the second knee at 200–300 PeV) as well as a $<\ln A>$ (E) dependence measured recently by the Tunka-133 experiment, is presented. We show that these features are compatible with the combined model where cosmic rays around the knee are produced by the group of dedicated sources and the extragalactic light component appears in the energy region of 10¹⁶–${10}^{17}\text{eV}$ and reaches about 50% of all particles around (2–3)$\times {10}^{17}\text{eV}$.

We analyze the results of recent measurements of Galactic cosmic ray (GCRs) energy spectra and the spectra of nonthermal emission from supernova remnants (SNRs) in order to determine their consistency with GCR origin in SNRs. It is shown that the measured primary and secondary CR nuclei energy spectra as well as the observed positron-to-electron ratio are consistent with the origin of GCRs up to the energy 10¹⁷ eV in SNRs. Existing SNR emission data provide evidences for efficient CR production in SNRs accompanied by significant magnetic field amplification. In some cases the nature of the detected γ-ray emission is difficult to determine because key SNR parameters are not known or poorly constrained.