165 research outputs found
Annihilation emission from young supernova remnants
A promising source of the positrons that contribute through annihilation to
the diffuse Galactic 511keV emission is the beta-decay of unstable nuclei like
56Ni and 44Ti synthesised by massive stars and supernovae. Although a large
fraction of these positrons annihilate in the ejecta of SNe/SNRs, no
point-source of annihilation radiation appears in the INTEGRAL/SPI map of the
511keV emission. We exploit the absence of detectable annihilation emission
from young local SNe/SNRs to derive constraints on the transport of MeV
positrons inside SN/SNR ejecta and their escape into the CSM/ISM, both aspects
being crucial to the understanding of the observed Galactic 511keV emission. We
simulated 511keV lightcurves resulting from the annihilation of the decay
positrons of 56Ni and 44Ti in SNe/SNRs and their surroundings using a simple
model. We computed specific 511keV lightcurves for Cas A, Tycho, Kepler,
SN1006, G1.9+0.3 and SN1987A, and compared these to the upper-limits derived
from INTEGRAL/SPI observations. The predicted 511keV signals from positrons
annihilating in the ejecta are below the sensitivity of the SPI instrument by
several orders of magnitude, but the predicted 511keV signals for positrons
escaping the ejecta and annihilating in the surrounding medium allowed to
derive upper-limits on the positron escape fraction of ~13% for Cas A, ~12% for
Tycho, ~30% for Kepler and ~33% for SN1006. The transport of ~MeV positrons
inside SNe/SNRs cannot be constrained from current observations of the 511keV
emission from these objects, but the limits obtained on their escape fraction
are consistent with a nucleosynthesis origin of the positrons that give rise to
the diffuse Galactic 511keV emission.Comment: 15 pages, 11 figures, accepted for publication in A&
Operations of and Future Plans for the Pierre Auger Observatory
Technical reports on operations and features of the Pierre Auger Observatory,
including ongoing and planned enhancements and the status of the future
northern hemisphere portion of the Observatory. Contributions to the 31st
International Cosmic Ray Conference, Lodz, Poland, July 2009.Comment: Contributions to the 31st ICRC, Lodz, Poland, July 200
Measurement of the Depth of Maximum of Extensive Air Showers above 10^18 eV
We describe the measurement of the depth of maximum, Xmax, of the
longitudinal development of air showers induced by cosmic rays. Almost four
thousand events above 10^18 eV observed by the fluorescence detector of the
Pierre Auger Observatory in coincidence with at least one surface detector
station are selected for the analysis. The average shower maximum was found to
evolve with energy at a rate of (106 +35/-21) g/cm^2/decade below 10^(18.24 +/-
0.05) eV and (24 +/- 3) g/cm^2/decade above this energy. The measured
shower-to-shower fluctuations decrease from about 55 to 26 g/cm^2. The
interpretation of these results in terms of the cosmic ray mass composition is
briefly discussed.Comment: Accepted for publication by PR
The Pierre Auger Observatory III: Other Astrophysical Observations
Astrophysical observations of ultra-high-energy cosmic rays with the Pierre
Auger ObservatoryComment: Contributions to the 32nd International Cosmic Ray Conference,
Beijing, China, August 201
Anisotropy and chemical composition of ultra-high energy cosmic rays using arrival directions measured by the Pierre Auger Observatory
The Pierre Auger Collaboration has reported evidence for anisotropy in the
distribution of arrival directions of the cosmic rays with energies
eV. These show a correlation with the distribution
of nearby extragalactic objects, including an apparent excess around the
direction of Centaurus A. If the particles responsible for these excesses at
are heavy nuclei with charge , the proton component of the
sources should lead to excesses in the same regions at energies . We here
report the lack of anisotropies in these directions at energies above
(for illustrative values of ). If the anisotropies
above are due to nuclei with charge , and under reasonable
assumptions about the acceleration process, these observations imply stringent
constraints on the allowed proton fraction at the lower energies
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
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