697 research outputs found
The Small Contribution of Molecular Bremsstrahlung Radiation to the Air-Fluorescence Yield of Cosmic Ray Shower Particles
A small contribution of molecular Bremsstrahlung radiation to the
air-fluorescence yield in the UV range is estimated based on an approach
previously developed in the framework of the radio-detection of showers in the
gigahertz frequency range. First, this approach is shown to provide an estimate
of the main contribution of the fluorescence yield due to the de-excitation of
the C electronic level of nitrogen molecules to the B
one amounting to MeV at
800 hPa pressure and 293 K temperature conditions, which compares well to
previous dedicated works and to experimental results. Then, under the same
pressure and temperature conditions, the fluorescence yield induced by
molecular Bremsstrahlung radiation is found to be
MeV in the wavelength range of
interest for the air-fluorescence detectors used to detect extensive air
showers induced in the atmosphere by ultra-high energy cosmic rays. This means
that out of photons with wavelength between 330 and 400 nm
detected by fluorescence detectors, one of them has been produced by molecular
Bremsstrahlung radiation. Although small, this contribution is not negligible
in regards to the total budget of systematic uncertainties when considering the
absolute energy scale of fluorescence detectors.Comment: 9 pages, 2 figures, accepted for publication in Astropart. Phys.
arXiv admin note: text overlap with arXiv:1601.0055
An Estimate of the Spectral Intensity Expected from the Molecular Bremsstrahlung Radiation in Extensive Air Showers
A detection technique of ultra-high energy cosmic rays, complementary to the
fluorescence technique, would be the use of the molecular Bremsstrahlung
radiation emitted by low-energy electrons left after the passage of the showers
in the atmosphere. The emission mechanism is expected from quasi-elastic
collisions of electrons produced in the shower by the ionisation of the
molecules in the atmosphere. In this article, a detailed calculation of the
spectral intensity of photons at ground level originating from the transitions
between unquantised energy states of free ionisation electrons is presented. In
the absence of absorption of the emitted photons in the plasma, the obtained
spectral intensity is shown to be 5 10^{-26} W m^{-2}Hz^{-1} at 10 km from the
shower core for a vertical shower induced by a proton of 10^{17.5} eV.Comment: 16 pages, 6 figures, accepted in Astroparticle Physics. Compared to
v1 version: 1. Inclusion of ro-vibrational processes. 2. Use of more accurate
ionization potential values and energy distribution of the secondary
electron
Molecular Bremsstrahlung Radiation at GHz Frequencies in Air
A detection technique for ultra-high energy cosmic rays, complementary to the
fluorescence technique, would be the use of the molecular Bremsstrahlung
radiation emitted by low-energy ionization electrons left after the passage of
the showers in the atmosphere. In this article, a detailed estimate of the
spectral intensity of photons at ground level originating from this radiation
is presented. The spectral intensity expected from the passage of the
high-energy electrons of the cascade is also estimated. The absorption of the
photons in the plasma of electrons/neutral molecules is shown to be negligible.
The obtained spectral intensity is shown to be W cm
GHz at 10 km from the shower core for a vertical shower induced by a
proton of eV. In addition, a recent measurement of Bremsstrahlung
radiation in air at gigahertz frequencies from a beam of electrons produced at
95 keV by an electron gun is also discussed and reasonably reproduced by the
model.Comment: 20 pages, 9 figures, figures (2,4,7) improved in v2, accepted by
Phys. Rev.
Angular Power Spectrum Estimation of Cosmic Ray Anisotropies with Full or Partial Sky Coverage
We study the angular power spectrum estimate in order to search for large
scale anisotropies in the arrival directions distribution of the highest-energy
cosmic rays. We show that this estimate can be performed even in the case of
partial sky coverage and validated over the full sky under the assumption that
the observed fluctuations are statistically spatial stationary. If this
hypothesis - which can be tested directly on the data - is not satisfied, it
would prove, of course, that the cosmic ray sky is non isotropic but also that
the power spectrum is not an appropriate tool to represent its anisotropies,
whatever the sky coverage available. We apply the method to simulations of the
Pierre Auger Observatory, reconstructing an input power spectrum with the
Southern site only and with both Northern and Southern ones. Finally, we show
the improvement that a full-sky observatory brings to test an isotropic
distribution, and we discuss the sensitivity of the Pierre Auger Observatory to
large scale anisotropies.Comment: 16 pages, 6 figures, version accepted for publication by JCA
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