740 research outputs found
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.
Estimates of multipolar coefficients to search for cosmic ray anisotropies with non-uniform or partial sky coverage
We study the possibility to extract the multipolar moments of an underlying
distribution from a set of cosmic rays observed with non-uniform or even
partial sky coverage. We show that if the degree is assumed to be upper bounded
by , each multipolar moment can be recovered whatever the coverage, but with
a variance increasing exponentially with the bound if the coverage is zero
somewhere. Despite this limitation, we show the possibility to test predictions
of a model without any assumption on by building an estimate of the
covariance matrix seen through the exposure function.Comment: 20 pages, 8 figure
The Use of the Signal at an Optimal Distance from the Shower Core as a Surrogate for Shower Size
When analysing data from air-shower arrays, it has become common practice to use the signal at a considerable distance from the shower axis (ropt) as a surrogate for the size of the shower. This signal, S(ropt), can then be related to the primary energy in a variety of ways. After a brief review of the reasons behind the introduction of ropt laid out in a seminal paper by Hillas in 1969, it will be shown that ropt, is a more effective tool when detectors are laid out on a triangular grid than when detectors are deployed on a square grid. This result may have implications for explaining the differences between the flux observed by the Auger and Telescope collaborations above 10\,EeV and should be kept in mind when designing new shower arrays
The Use of the Signal at an Optimal Distance from the Shower Core as a Surrogate for Shower Size
When analysing data from air-shower arrays, it has become common practice to use the signal at a considerable distance from the shower axis (_opt) as a surrogate for the size of the shower. This
signal, (_opt), can then be related to the primary energy in a variety of ways. After a brief review of the reasons behind the introduction of opt laid out in a seminal paper by Hillas in 1969, it will be shown that _opt, is a more effective tool when detectors are laid out on a triangular grid than when detectors are deployed on a square grid. This result may have implications for explaining the differences between the flux observed by the Auger and Telescope collaborations above 10 EeV and should be kept in mind when designing new shower arrays
Temporal profiling of the heat-stable proteome during late maturation of Medicago truncatula seeds identifies a restricted subset of late embryogenesis abundant proteins associated with longevity
Developing seeds accumulate late embryogenesis abundant (LEA) proteins, a family of intrinsically disordered and hydrophilic proteins that confer cellular protection upon stress. Many different LEA proteins exist in seeds, but their relative contribution to seed desiccation tolerance or longevity (duration of survival) is not yet investigated. To address this, a reference map of LEA proteins was established by proteomics on a hydrophilic protein fraction from mature Medicago truncatula seeds and identified 35 polypeptides encoded by 16 LEA genes. Spatial and temporal expression profiles of the LEA polypeptides were obtained during the long maturation phase during which desiccation tolerance and longevity are sequentially acquired until pod abscission and final maturation drying occurs. Five LEA polypeptides, representing 6% of the total LEA intensity, accumulated upon acquisition of desiccation tolerance. The gradual 30-fold increase in longevity correlated with the accumulation of four LEA polypeptides, representing 35% of LEA in mature seeds, and with two chaperone-related polypeptides. The majority of LEA polypeptides increased around pod abscission during final maturation drying. The differential accumulation profiles of the LEA polypeptides suggest different roles in seed physiology, with a small subset of LEA and other proteins with chaperone-like functions correlating with desiccation tolerance and longevity
2022 report from the Auger-TA working group on UHECR arrival directions
After over 60 years, the powerful engines that accelerate ultra-high-energy
cosmic rays (UHECRs) to the formidable energies at which we observe them from
Earth remain mysterious. Assuming standard physics, we expect UHECR sources to
lie within the local Universe (up to a few hundred~Mpc). The distribution of
matter in the local Universe is anisotropic, and we expect this anisotropy to
be imprinted on the distribution of UHECR arrival directions. Even though
intervening intergalactic and Galactic magnetic fields deflect charged UHECRs
and can distort these anisotropies, some amount of information on the
distribution of the sources is preserved. In this proceedings contribution, we
present the results of the joint Pierre Auger Observatory and Telescope Array
searches for (a) the largest-scale anisotropies (the harmonic dipole and
quadrupole) and (b) correlations with a sample of nearby starburst galaxies and
the 2MRS catalogue tracing stellar mass within~250~Mpc. This analysis updates
our previous results with the most recent available data, notably with the
addition of 3~years of new Telescope Array data. The main finding is a
correlation between the arrival directions of ~of
UHECRs detected with ~EeV by~Auger or with~~EeV by~TA
and the positions of nearby starburst galaxies on a
~angular scale, with a
~post-trial significance, up from obtained in our
previous study.Comment: proceedings of the 6th International Symposium on Ultra High Energy
Cosmic Rays (UHECR2022), 3-7 October 2022, L'Aquila, Ital
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
A search for point sources of EeV photons
Measurements of air showers made using the hybrid technique developed with
the fluorescence and surface detectors of the Pierre Auger Observatory allow a
sensitive search for point sources of EeV photons anywhere in the exposed sky.
A multivariate analysis reduces the background of hadronic cosmic rays. The
search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an
energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been
detected. An upper limit on the photon flux has been derived for every
direction. The mean value of the energy flux limit that results from this,
assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial
direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in
which EeV cosmic ray protons are emitted by non-transient sources in the
Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical
Journa
Reconstruction of inclined air showers detected with the Pierre Auger Observatory
We describe the method devised to reconstruct inclined cosmic-ray air showers
with zenith angles greater than detected with the surface array of
the Pierre Auger Observatory. The measured signals at the ground level are
fitted to muon density distributions predicted with atmospheric cascade models
to obtain the relative shower size as an overall normalization parameter. The
method is evaluated using simulated showers to test its performance. The energy
of the cosmic rays is calibrated using a sub-sample of events reconstructed
with both the fluorescence and surface array techniques. The reconstruction
method described here provides the basis of complementary analyses including an
independent measurement of the energy spectrum of ultra-high energy cosmic rays
using very inclined events collected by the Pierre Auger Observatory.Comment: 27 pages, 19 figures, accepted for publication in Journal of
Cosmology and Astroparticle Physics (JCAP
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