951 research outputs found
Description of Atmospheric Conditions at the Pierre Auger Observatory Using Meteorological Measurements and Models
Atmospheric conditions at the site of a cosmic ray observatory must be known
well for reconstructing observed extensive air showers, especially when
measured using the fluorescence technique. For the Pierre Auger Observatory, a
sophisticated network of atmospheric monitoring devices has been conceived.
Part of this monitoring was a weather balloon program to measure atmospheric
state variables above the Observatory. To use the data in reconstructions of
air showers, monthly models have been constructed. Scheduled balloon launches
were abandoned and replaced with launches triggered by high-energetic air
showers as part of a rapid monitoring system. Currently, the balloon launch
program is halted and atmospheric data from numerical weather prediction models
are used. A description of the balloon measurements, the monthly models as well
as the data from the numerical weather prediction are presented
Comparison of available measurements of the absolute fluorescence yield
The uncertainty in the absolute value of the fluorescence yield is still one
of the main contributions to the total error in the reconstruction of the
primary energy of ultra-energetic air showers using the fluorescence technique.
A significant number of experimental values of the fluorescence yield have been
published in the last years, however reported results are given very often in
different units (photons/MeV or photons/m) and for different wavelength
intervals. In this work we present a comparison of available results normalized
to its value in photons/MeV for the 337 nm band at 800 hPa and 293 K. The
conversion of photons/m to photons/MeV requires an accurate determination of
the energy deposited by the electrons in the field of view of the experimental
setup. We have calculated the energy deposition for each experiment by means of
a detailed Monte Carlo simulation including when possible the geometrical
details of the particular setup. Our predictions on deposited energy, as well
as on some geometrical factors, have been compared with those reported by the
authors of the corresponding experiments and possible corrections to the
fluorescence yields are proposed.Comment: 29 pages, 5 figures Revised version submitted to Astroparticle
Physic
Characteristics of geomagnetic cascading of ultra-high energy photons at the southern and northern sites of the Pierre Auger Observatory
Cosmic-ray photons above 10^19 eV can convert in the geomagnetic field and
initiate a preshower, i.e. a particle cascade before entering the atmosphere.
We compare the preshower characteristics at the southern and northern sites of
the Pierre Auger Observatory. In addition to a shift of the preshower patterns
on the sky due to the different pointing of the local magnetic field vectors,
the fact that the northern Auger site is closer to the geomagnetic pole results
in a different energy dependence of the preshower effect: photon conversion can
start at smaller energies, but large conversion probabilitites (>90%) are
reached for the whole sky at higher energies compared to the southern Auger
site. We show how the complementary preshower features at the two sites can be
used to search for ultra-high energy photons among cosmic rays. In particular,
the different preshower characteristics at the northern Auger site may provide
an elegant and unambiguous confirmation if a photon signal is detected at the
southern site.Comment: 25 pages, 14 figures, minor changes, conclusions unchanged, Appendix
A replaced, accepted by Astroparticle Physic
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