207 research outputs found
Nearby supernova remnants and the cosmic-ray spectral hardening at high energies
Recent measurements of cosmic-ray spectra of several individual nuclear
species by the CREAM, TRACER, and ATIC experiments indicate a change in the
spectral index of the power laws at TeV energies. Possible explanations among
others include non linear diffusive shock acceleration of cosmic-rays,
different cosmic-ray propagation properties at higher and lower energies in the
Galaxy and the presence of nearby sources. In this paper, we show that if
supernova remnants are the main sources of cosmic rays in our Galaxy, the
effect of the nearby remnants can be responsible for the observed spectral
changes. Using a rigidity dependent escape of cosmic-rays from the supernova
remnants, we explain the apparent observed property that the hardening of the
helium spectrum occurs at relatively lower energies as compared to the protons
and also that the spectral hardening does not persist beyond TeV
energies.Comment: 6 pages, MNRAS accepted, minor text correction
GeV-TeV cosmic-ray spectral anomaly as due to re-acceleration by weak shocks in the Galaxy
Recent cosmic-ray measurements have found an anomaly in the cosmic-ray energy
spectrum at GeV-TeV energies. Although the origin of the anomaly is not clearly
understood, suggested explanations include effect of cosmic-ray source
spectrum, propagation effects, and the effect of nearby sources. In this paper,
we propose that the spectral anomaly might be an effect of re-acceleration of
cosmic rays by weak shocks in the Galaxy. After acceleration by strong
supernova remnant shock waves, cosmic rays undergo diffusive propagation
through the Galaxy. During the propagation, cosmic rays may again encounter
expanding supernova remnant shock waves, and get re-accelerated. As the
probability of encountering old supernova remnants is expected to be larger
than the younger ones due to their bigger sizes, re-acceleration is expected to
be mainly due to weaker shocks. Since weaker shocks generate a softer particle
spectrum, the resulting re-accelerated component will have a spectrum steeper
than the initial cosmic-ray source spectrum produced by strong shocks. For a
reasonable set of model parameters, it is shown that such re-accelerated
component can dominate the GeV energy region while the non-reaccelerated
component dominates at higher energies, explaining the observed GeV-TeV
spectral anomaly.Comment: 12 pages, A&A accepte
GCOS -- The Global Cosmic Ray Observatory
Nature is providing particles with energies exceeding 100 EeV. Their
existence imposes immediate questions: Are they ordinary particles, accelerated
in extreme astrophysical environments, or are they annihilation or decay
products of super-heavy dark matter or other exotic objects? If the particles
are accelerated in extreme astrophysical environments, are their sources
related to those of high-energy neutrinos, gamma rays, and/or gravitational
waves, such as the recently observed mergers of compact objects? The particles
can also be used to study physics processes at extreme energies; is Lorentz
invariance still valid? Are the particles interacting according to the Standard
Model or are there new physics processes? The particles can be used to study
hadronic interactions (QCD) in the kinematic forward direction; what is the
cross section of protons at center-of-mass energies TeV?
These questions are addressed at present by installations like the Telescope
Array and the Pierre Auger Observatory. After the year 2030, a next-generation
observatory will be needed to study the physics and properties of the
highest-energy particles in Nature, building on the knowledge harvested from
the existing observatories. It should have an aperture at least an order of
magnitude bigger than the existing observatories. Recently, more than 200
scientists from around the world came together to discuss the future of the
field of multi-messenger astroparticle physics beyond the year 2030. Ideas have
been discussed towards the physics case and possible scenarios for detection
concepts of the Global Cosmic Ray Observatory - GCOS. A synopsis of the key
results discussed during the brainstorming workshop will be presented
Cosmogenic gamma-rays and neutrinos constrain UHECR source models
We use CRPropa 3 to show how the expected cosmogenic neutrino and gamma-ray
spectra depend on the maximum energy of ultra-high energy cosmic rays (UHECRs)
at their sources, on the spectral index at injection and on the chemical
composition of UHECRs. The isotropic diffuse gamma-ray background measured by
Fermi/LAT is already close to touching upon a model with co-moving source
evolution and with the chemical composition, spectral index and maximum
acceleration energy optimized to provide the best fit to the UHECR spectrum and
composition measured by the Pierre Auger Collaboration. Additionally, the
detectable fraction of protons present at the highest energies in UHECRs, for
experiments with sensitivities to the single-flavor neutrino flux at
EeV in the range of - GeV cm s
sr, is shown as a function of the evolution of UHECR sources.
Experiments that reach this sensitivity will be able to significantly constrain
the proton fraction for realistic source evolution models.Comment: Proc. 35th ICRC, Busan, South Korea, PoS(ICRC2017)56
The origin of galactic cosmic rays
The origin of galactic cosmic rays is one of the most interesting unsolved
problems in astroparticle physics. Experimentally, the problem is attacked by a
multi-disciplinary effort, namely by direct measurements of cosmic rays above
the atmosphere, by air shower observations, and by the detection of TeV
rays. Recent experimental results are presented and their implications
on the contemporary understanding of the origin of galactic cosmic rays are
discussed.Comment: Invited talk given at the Roma International Conference on
Astro-Particle physics (RICAP07) June 20th - 22nd, 2007. To be published in
Nuclear Instruments and Methods
Models of the Knee in the Energy Spectrum of Cosmic Rays
The origin of the knee in the energy spectrum of cosmic rays is an
outstanding problem in astroparticle physics. Numerous mechanisms have been
proposed to explain the structure in the all-particle spectrum. In the article
basic ideas of several models are summarized, including diffusive acceleration
of cosmic rays in shock fronts, acceleration via cannonballs, leakage from the
Galaxy, interactions with background particles in the interstellar medium, as
well as new high-energy interactions in the atmosphere. The calculated energy
spectra and mean logarithmic masses are compiled and compared to results from
direct and indirect measurements.Comment: 30 pages, 20 figures accepted by Astroparticle Physics captions of
figures 1-3 clarified, references adde
Cosmic-ray composition and its relation to shock acceleration by supernova remnants
An overview is given on the present status of the understanding of the origin
of galactic cosmic rays. Recent measurements of charged cosmic rays and photons
are reviewed. Their impact on the contemporary knowledge about the sources and
acceleration mechanisms of cosmic rays and their propagation through the Galaxy
is discussed. Possible reasons for the knee in the energy spectrum and
scenarios for the end of the galactic cosmic-ray component are described.Comment: Invited talk given at the 36th COSPAR Scientific Assembly Beijing,
China, 16 -- 23 July 2006 - submitted to Advances in Space Research -
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