Nuclear physics. B, Proceedings, supplements最新文献

In addition to efficient particle accelerators in the Galaxy, such as supernova remnants and pulsar wind nebulae, other sources can accelerate particles up to very high energies. We present the case of protostellar jets and runaway stars, where strong shocks act upon electrons and protons through a diffusive process. The detection of synchrotron radio emission from these sources indicates that at least electrons are accelerated in these systems. If protons are accelerated as well, both population of relativistic particles can produce high-energy radiation through a variety of processes. We show results from models of the non-thermal emission, from radio to gamma rays, in these kind of sources. High-energy photons from both protostellar jets and massive runaways might be detectable with the current facilities in the GeV domain, or by the forthcoming Cherenkov arrays. A clear detection would prove that young stars are also cosmic ray accelerators.

We analyse the high energy processes, occurring within open clusters containing massive binary systems, which turn to the production of high energy γ-rays and neutrinos. Nuclei, accelerated within the binary systems, inject protons and neutrons as a result of their fragmentation in collisions with stellar radiation and matter of the winds. We calculate the radiation produced by these protons and neutrons during their interaction with the matter of the stellar wind and the open cluster. The detectability of γ-ray emission and neutrino emission by the present and future Cherenkov telescopes and the neutrino telescopes is discussed.

The intensity of extraterrestrial neutrinos discovered by IceCube [M. G. Aartsen et al. (IceCube Collaboration), Science 342 (2013) 1242856] is in reasonable agreement with predictions of neutrinos from the jets of active galactic nuclei due to pion production by accelerated protons [K. Mannheim, Astropart. Phys. 3 (1995) 295]. The observed deficit of Glashow-resonance events at 6.3 PeV could result from the suppression of events with energies larger than PeV due to the presence of a strong “big blue bump” radiation field in flat-spectrum radio quasars. The total neutrino spectrum could exhibit a two-component structure in which the sub-PeV component is dominated by the jets from AGN with high accretion rates and another component peaking at EeV energies due to those with low accretion rates. Each component of the neutrino spectrum should carry the energy flux that corresponds to its relative contribution to the extragalactic gamma ray background. The arrival directions should correlate with known sources, and a simple test shows that the PeV events can indeed be explained by known blazars with prominent radio jets. If a Galactic component of cosmic rays with energies per nucleon above knee energies exists, as air shower array data seem to indicate, the neutrinos due to pion production from these sources are also detectable, pinpointing them an energies where gamma-ray observations are not yet possible.

In the last years the direct measurement of cosmic rays received a push forward by the possibility of conducting experiments on board long duration balloon flights, satellites and on the International Space Station. The increase in the collected statistics and the technical improvements in the construction of the detectors permit the fluxes measurement to be performed at higher energies with a reduced discrepancy among different experiments respect to the past. However, high statistical precision is not always associated to the needed precision in the estimation of systematics; features in the particle spectra can be erroneously introduced or hidden. A review and a comparison of the latest experimental results on direct cosmic rays measurements will be presented with particular emphasis on their similarities and discrepancies.

Galactic Supernova Remnants (SNRs) are among the best candidates as source of cosmic rays due to energetics, observed rate of explosion and as possible sites where the Fermi mechanisms naturally plays a key role. Evidence of hadronic acceleration processes taking place in SNRs are being collected with the Fermi-LAT, whose sensitivity in the range 100MeV–100GeV is crucial for disentangling possible hadronic contribution from inverse Compton or bremsstrahlung leptonic component. A survey of the detected SNRs will be given, focusing the attention on the role of the environment and the evolution stage of the SNR in the interpretation of the observed γ-ray spectra.

The search for a theory of the origin of cosmic rays that may be considered as a standard, agreeable model is still ongoing. On one hand, much circumstantial evidence exists of the fact that supernovae in our Galaxy play a crucial role in producing the bulk of cosmic rays observed on Earth. On the other hand, important questions about their ability to accelerate particles up to the knee remain unanswered. The common interpretation of the knee as a feature coinciding with the maximum energy of the light component of cosmic rays and a transition to a gradually heavier mass composition is mainly based on KASCADE results. Some recent data appear to question this finding: YAC1 – Tibet Array and ARGO-YBJ find a flux reduction in the light component at ∼ 700 TeV, appreciably below the knee. Whether the maximum energy of light nuclei is as high as 3000 TeV or rather as low as a few hundred TeV has very important consequences on the supernova remnant paradigm for the origin of cosmic rays, as well on the crucial issue of the transition from Galactic to extragalactic cosmic rays. In such a complex phenomenological situation, it is important to have a clear picture of what is really known and what is not. Here I will discuss some solid and less solid aspects of the theory (or theories) for the origin of cosmic rays and the implications for future searches in this field.

The shocks of several young supernova remnants (SNR) are often associated with very thin optical filaments dominated by Balmer emission resulting from charge-exchange and collisional excitation between neutral Hydrogen from the interstellar medium and shocked protons and electrons. Optical lines are a direct probe of the conditions at the shock, in particular the width of the narrow and broad components reflect the temperature upstream and downstream of the shock, respectively. When the shock accelerate efficiently non-thermal particles, the shock structure changes producing anomalous Balmer lines and it is possible to use their line shape and their spatial profile to check the efficiency of SNR shocks in accelerating cosmic rays. Here we illustrate the kinetic theory of shock acceleration in presence of neutrals with some applications to young SNRs. We show that in three cases (RCW 86, SNR 0509-67.5 and Tycho) anomalous Balmer lines can be explained assuming that a fraction of ∼ 10% of the total shock kinetic energy is converted into not thermal particles, while in one single case, the northwestern part of SN 1006, there is no evidence of efficient acceleration.

Young pulsars have been scarcely discussed as sources of high and ultrahigh energy cosmic rays (UHECR) in the literature. However, the production of UHECRs in these objects could give a picture that is surprisingly consistent with the latest data measured with the Auger Observatory. Here we discuss the production of high and UHE cosmic rays in pulsars. We compare the propagated UHECR observables from the pulsar population with the available data. Finally, we discuss signatures of such a scenario, that one could find in the diffusive neutrino backgrounds and in the lightcurves of supernovae.