1,884 research outputs found
Neutrinos from active black holes, sources of ultra high energy cosmic rays
A correlation between the highest energy Cosmic Rays (above ~ EeV) and the
distribution of active galactic nuclei (AGN) gives rise to a prediction of
neutrino production in the same sources. In this paper, we present a detailed
AGN model, predicting neutrino production near the foot of the jet, where the
photon fields from the disk and synchrotron radiation from the jet itself
create high optical depths for proton-photon interactions. The protons escape
from later shocks where the emission region is optically thin for proton-photon
interactions. Consequently, Cosmic Rays are predicted to come from FR-I
galaxies, independent of the orientation of the source. Neutrinos, on the other
hand, are only observable from sources directing their jet towards Earth, i.e.
flat spectrum radio sources and in particular BL Lac type objects, due to the
strongly boosted neutrino emission.Comment: Accepted for publication in Astroparticle Physics; 30 pages, 8
figure
Theoretical study of ionization profiles of molecular clouds near supernova remnants: Tracing the hadronic origin of GeV gamma radiation
Context: Since a few years, signatures of supernova remnants associated with
molecular clouds have been detected in gamma rays. Whether these gamma rays are
generated by cosmic ray electrons or by cosmic ray protons is usually not
known. The detection of hadronic ionization signatures in spatial coincidence
with gamma ray signatures can help to unambiguously identify supernova remnants
as sources of cosmic ray protons.
Methods: In order to calculate hadronic signatures from cosmic ray-induced
ionization for an examination of the origin of the observed gamma rays, the
transport equation for cosmic ray protons propagating in a molecular cloud,
including the relevant momentum loss processes, is solved analytically and the
proton flux at any position in the cloud is determined.
Results: Since the solution of the transport equation is obtained for
arbitrary source functions, it can be used for a variety of supernova remnants.
The corresponding theoretical ionization rate, as a function of the penetration
depth, is derived and compared to photoinduced ionization profiles in a case
study with four supernova remnants associated with molecular clouds. Three of
the remnants show a clear dominance of the hadronically induced ionization
rate, while for one remnant, X-ray emission seems to dominate by a factor of
10.
Conclusions: This is the first derivation of position-dependent profiles for
cosmic ray-induced ionization with an analytic solution for arbitrary cosmic
ray source spectra. The cosmic ray-induced ionization has to be compared to
X-ray ionization for strong X-ray sources. For sources dominated by cosmic
ray-induced ionization (e.g., W49B), the ionization profiles can be used in the
future to map the spatial structure of hadronic gamma rays and
rotation-vibrational lines induced by cosmic ray protons, helping to identify
sources of hadronic cosmic rays.Comment: published in Astronomy and Astrophysics, 20 pages, 17 figure
The diffuse neutrino flux from FR-II radio galaxies and blazars: A source property based estimate
Water and ice Cherenkov telescopes of the present and future aim for the
detection of a neutrino signal from extraterrestrial sources at energies E>PeV.
Some of the most promising extragalactic sources are Active Galactic Nuclei
(AGN). In this paper, the neutrino flux from two kinds of AGN sources will be
estimated assuming photohadronic interactions in the jet of the AGN. The first
analyzed sample contains FR-II radio galaxies while the second AGN type
examined are blazars. The result is highly dependent on the proton's index of
the energy spectrum. To normalize the spectrum, the connection between neutrino
and disk luminosity will be used by applying the jet-disk symbiosis model from
Falcke and Biermann (1995). The maximum proton energy and thus, also the
maximum neutrino energy of the source is connected to its disk luminosity,
which was shown by Lovelace (1976) and was confirmed by Falcke et al. (1995).Comment: 24 pages, 14 figures, to be published in Astroparticle Physic
Impact of Secondary Acceleration in Gamma-Ray Bursts
We discuss the acceleration of secondary muons, pions, and kaons in gamma-ray
bursts within the internal shock scenario, and their impact on the neutrino
fluxes. We introduce a two-zone model consisting of an acceleration zone (the
shocks) and a radiation zone (the plasma downstream the shocks). The
acceleration in the shocks, which is an unavoidable consequence of the
efficient proton acceleration, requires efficient transport from the radiation
back to the acceleration zone. On the other hand, stochastic acceleration in
the radiation zone can enhance the secondary spectra of muons and kaons
significantly if there is a sufficiently large turbulent region. Overall, it is
plausible that neutrino spectra can be enhanced by up to a factor of two at the
peak by stochastic acceleration, that an additional spectral peaks appears from
shock acceleration of the secondary muons and pions, and that the neutrino
production from kaon decays is enhanced. Depending on the GRB parameters, the
general conclusions concerning the limits to the internal shock scenario
obtained by recent IceCube and ANTARES analyses may be affected by up to a
factor of two by secondary acceleration. Most of the changes occur at energies
above 10^7 GeV, so the effects for next-generation radio-detection experiments
will be more pronounced. In the future, however, if GRBs are detected as
high-energy neutrino sources, the detection of one or several pronounced peaks
around 10^6 GeV or higher energies could help to derive the basic properties of
the magnetic field strength in the GRB.Comment: 10 pages, 5 figures, 1 tabl
Dreamers and Donald Trump: Anti-Trump Street Art Along the US-Mexico Border
What tools are at hand for residents living on the US-Mexico border to respond to mainstream news and presidential-driven narratives about immigrants, immigration, and the border region? How do citizen activists living far from the border contend with President Trump’s promises to “build the wall,” enact immigration bans, and deport the millions of undocumented immigrants living in the United States? How do situated, highly localized pieces of street art engage with new media to become creative and internationally resonant sites of defiance?
CARGC Paper 11, “Dreamers and Donald Trump: Anti-Trump Street Art Along the US-Mexico Border,” answers these questions through a textual analysis of street art in the border region. Drawing on her Undergraduate Honors Thesis and fieldwork she conducted at border sites in Texas, California, and Mexico in early 2018, former CARGC Undergraduate Fellow Julia Becker takes stock of the political climate in the US and Mexico, examines Donald Trump’s rhetoric about immigration, and analyzes how street art situated at the border becomes a medium of protest in response to that rhetoric.https://repository.upenn.edu/cargc_papers/1011/thumbnail.jp
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