1,238 research outputs found
The galactic gamma-ray distribution: Implications for galactic structure and the radial cosmic ray gradient
The radial distribution of gamma ray emissivity in the Galaxy was derived from flux longitude profiles, using both the final SAS-2 results and the recently corrected COS-B results and analyzing the northern and southern galactic regions separately. The recent CO surveys of the Southern Hemisphere, were used in conjunction with the Northern Hemisphere data, to derive the radial distribution of cosmic rays on both sides of the galactic plane. In addition to the 5 kpc ring, there is evidence from the radial asymmetry for spiral features which are consistent with those derived from the distribution of bright HII regions. Positive evidence was also found for a strong increase in the cosmic ray flux in the inner Galaxy, particularly in the 5 kpc region in both halves of the plane
Comment on ``Cosmological Gamma Ray Bursts and the Highest Energy Cosmic Rays''
In a letter with the above title, published some time ago in PRL, Waxman made
the interesting suggestion that cosmological gamma ray bursts (GRBs) are the
source of the ultra high energy cosmic rays (UHECR). This has also been
proposed independently by Milgrom and Usov and by Vietri. However, recent
observations of GRBs and their afterglows and in particular recent data from
the Akeno Great Air Shwoer Array (AGASA) on UHECR rule out extragalactic GRBs
as the source of UHECR.Comment: Comment on a letter with the above title published by E. Waxman in
PRL 75, 386 (1995). Submitted for publication in PRL/Comment
Pulsar and diffuse contributions to the observed galactic gamma radiation
With the acquisition of satellite data on the energy spectrum of galactic gamma-radiation, it is clear that such radiation has a multicomponent nature. A calculation of the pulsar gamma ray emission spectrum is used together with a statistical analysis of recent data on 328 known pulsars to make a new determination of the pulsar contribution to galactic gamma ray emission. The contributions from diffuse interstellar cosmic ray induced production mechanisms to the total emission are then reexamined. It is concluded that pulsars may account for a significant fraction of galactic gamma ray emission
Antiparticles in the extragalactic cosmic radiation
It may be possible to account for a previously puzzling feature - a bump in the energy range 10 to the 14th power eV to 10 to the 15th power - of the cosmic ray spectrum by hypothesizing a primary extragalactic origin for the bulk of the observed cosmic ray antiprotons, although such an explanation is not unique. In this model, most of the cosmic rays above 10 to the 15th power eV are extragalactic. A method is described of testing this hypothesis experimentally
Matter antimatter domains: A possible solution to the CP domain wall problem in the early universe
An SU(5) grand unified theory model is used to show how the degeneracy between vacua with different spontaneously broken charge parity can be dynamically lifted by a condensate of heavy fermion pairs. This drives a phase transition to a unique vacuum state with definite charge parity. The transition eliminates the domain walls in a matter antimatter symmetric domain cosmology
Shadowing of Ultrahigh Energy Neutrinos
The rise with energy of the neutrino--nucleon cross section implies that at
energies above few TeV the Earth is becoming opaque to cosmic neutrinos. The
neutrinos interact with the nucleons through the weak charged current,
resulting into absorption, and the weak neutral current, which provides a
redistribution of the neutrino energy. We Mellin transform the neutrino
transport equation and find its exact solution in the moment space. A simple
analytical formula is provided, which describes accurately the neutrino
spectrum, after the neutrinos have traversed the Earth. The effect of the weak
neutral current is most prominent for an initial flat neutrino spectrum and we
find that at low energies (around 1 TeV) the neutrino intensity is even
enhanced.Comment: gziped, tar file of LaTeX paper plus 2 postscript figures, 13 page
A Determination of the Intergalactic Redshift Dependent UV-Optical-NIR Photon Density Using Deep Galaxy Survey Data and the Gamma-ray Opacity of the Universe
We calculate the intensity and photon spectrum of the intergalactic
background light (IBL) as a function of redshift using an approach based on
observational data obtained in many different wavelength bands from local to
deep galaxy surveys. This allows us to obtain an empirical determination of the
IBL and to quantify its observationally based uncertainties. Using our results
on the IBL, we then place 68% confidence upper and lower limits on the opacity
of the universe to gamma-rays, free of the theoretical assumptions that were
needed for past calculations. We compare our results with measurements of the
extragalactic background light and upper limits obtained from observations made
by the Fermi Gamma-ray Space Telescope.Comment: 32 pages, 6 figures, Accepted for publication in the Astrophysical
Journa
Corrected Table for the Parametric Coefficients for the Optical Depth of the Universe to Gamma-rays at Various Redshifts
Table 1 in our paper, ApJ 648, 774 (2006) entitled "Intergalactic Photon
Spectra from the Far IR to the UV Lyman Limit for 0 < z < 6 and the Optical
Depth of the Universe to High Energy Gamma-Rays" had erroneous numbers for the
coefficients fitting the parametric form for the optical depth of the universe
to gamma-rays. The correct values for these parameters as described in the
original text are given here in a corrected table for various redshifts for the
baseline model (upper row) and fast evolution (lower row) for each individual
redshift. The parametric approximation is good for optical depths between 0.01
and 100 and for gamma-ray energies up to ~2 TeV for all redshifts but also for
energies up to ~10 TeV for redshifts less than 1.Comment: Table 1 corrected and new gamma-ray energy range of validity give
An Empirical Determination of the Intergalactic Background Light Using NIR Deep Galaxy Survey Data out to 5 microns and the Gamma-ray Opacity of the Universe
We extend our previous model-independent determination of the intergalactic
background light (IBL), based purely on galaxy survey data, out to a wavelength
of 5 microns. Our approach enables us to constrain the range of photon
densities, based on the uncertainties from observationally determined
luminosity densities and colors. We further determine a 68% confidence upper
and lower limit on the opacity of the universe to gamma-rays up to energies of
1.6/(1+z) TeV. A comparison of our lower limit redshift-dependent opacity
curves to the opacity limits derived from the results of both ground-based air
Cherenkov telescope and Fermi-LAT observations of PKS 1424+240 allows us to
place a new upper limit on the redshift of this source, independent of IBL
modeling.Comment: version accepted for publication in the Astrophysical Journal, 23
pages, 4 figure
An Empirical Determination of the Intergalactic Background Light from UV to FIR Wavelengths Using FIR Deep Galaxy Surveys and the Gamma-ray Opacity of the Universe
We have previously calculated the intergalactic background light (IBL) as a
function of redshift in the far ultraviolet to near infrared range, based
purely on data from deep galaxy surveys. Here we utilize similar methods to
determine the mid- and far infrared IBL out to a wavelength of 850 microns. Our
approach enables us to constrain the range of photon densities, based on the
uncertainties from observationally determined luminosity densities and colors.
By also including the effect of the 2.7 K cosmic background photons, we
determine 68% confidence upper and lower limits on the opacity of the universe
to gamma-rays up to PeV energies. Our direct results on the IBL are consistent
with those from complimentary gamma-ray analyses using observations from the
Fermi -ray space telescope and the H.E.S.S. air Cherenkov telescope.
Thus, we find no evidence of previously suggested processes for the
modification of gamma-ray spectra other than that of absorption by pair
production alone.Comment: 33 pages, 11 figures, replacement matches article published in ApJ
827:6 (2016
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