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Register a new userThe Optimum Distance at which to Determine the Size of a Giant Air Shower
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To determine the size of an extensive air shower it is not necessary to have knowledge of the function that describes the fall-off of signal size from the shower core (the lateral distribution function). In this paper an analysis with a simple Monte Carlo model is used to show that an optimum ground parameter can be identified for each individual shower. At this optimal core distance, $r_mathrm{opt}$, the fluctuations in the expected signal, $S(r_mathrm{opt})$, due to a lack of knowledge of the lateral distribution function are minimised. Furthermore it is shown that the optimum ground parameter is determined primarily by the array geometry, with little dependence on the energy or zenith angle of the shower or choice of lateral distribution function. For an array such as the Pierre Auger Southern Observatory, with detectors separated by 1500 m in a triangular configuration, the optimum distance at which to measure this characteristic signal is close to 1000 m.
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The size of the giant component in the configuration model, measured by the asymptotic fraction of vertices in the component, is given by a well-known expression involving the generating function of the degree distribution. In this note, we argue that the distribution over small degrees is more important for the size of the giant component than the precise distribution over very large degrees. In particular, the tail behavior of the degree distribution does not play the same crucial role for the size of the giant as it does for many other properties of the graph. Upper and lower bounds for the component size are derived for an arbitrary given distribution over small degrees $dleq L$ and given expected degree, and numerical implementations show that these bounds are close already for small values of $L$. On the other hand, examples illustrate that, for a fixed degree tail, the component size can vary substantially depending on the distribution over small degrees.
Using data from more than ten-years of observations with the Akeno Giant Air Shower Array (AGASA), we published a result that the energy spectrum of ultra-high energy cosmic rays extends beyond the cutoff energy predicted by Greisen, and Zatsepin and Kuzmin. In this paper, we reevaluate the energy determination method used for AGASA events with respect to the lateral distribution of shower particles, their attenuation with zenith angle, shower front structure, delayed particles observed far from the core and other factors. The currently assigned energies of AGASA events have an accuracy of $pm$25% in event-reconstruction resolution and $pm$18% in systematic errors around 10$^{20}$eV. This systematic uncertainty is independent of primary energy above 10$^{19}$eV. Based on the energy spectrum from 10$^{14.5}$eV to a few times 10$^{20}$eV determined at Akeno, there are surely events above 10$^{20}$eV and the energy spectrum extends up to a few times 10$^{20}$eV without a GZK-cutoff.
We observe a correlation between the slope of radio lateral distributions, and the mean muon pseudorapidity of 59 individual cosmic-ray-air-shower events. The radio lateral distributions are measured with LOPES, a digital radio interferometer co-located with the multi-detector-air-shower array KASCADE-Grande, which includes a muon-tracking detector. The result proves experimentally that radio measurements are sensitive to the longitudinal development of cosmic-ray air-showers. This is one of the main prerequisites for using radio arrays for ultra-high-energy particle physics and astrophysics.
Airless planetary bodies are covered by a dusty layer called regolith. The grain size of the regolith determines the temperature and the mechanical strength of the surface layers. Thus, knowledge of the grain size of planetary regolith helps to prepare future landing and/or sample-return missions. In this work, we present a method to determine the grain size of planetary regolith by using remote measurements of the thermal inertia. We found that small bodies in the Solar System (diameter less than ~100 km) are covered by relatively coarse regolith grains with typical particle sizes in the millimeter to centimeter regime, whereas large objects possess very fine regolith with grain sizes between 10 and 100 micrometer.
Stellar photometry in nine fields around the giant elliptical galaxy M87 in the Virgo cluster is obtained from archival images of the Hubble Space Telescope. The resulting Hertzsprung--Russell diagrams show populated red-giant and AGB branches. The position of the tip of the red-giant branch (the TRGB discontinuity) is found to vary with galactocentric distance. This variation can be interpreted as the effect of metal-rich red giants on the procedure of the measurement of the TRGB discontinuity or as a consequence of the existence of a weak gas-and-dust cloud around M87 extending out to $10^prime$ along the galactocentric radius and causing $I$-band absorption of up to $0.^m2$ near the center of the galaxy. The TRGB stars located far from the M87 center yield an average distance modulus of $(m-M) = 30.91pm0.08$, which corresponds to the distance of $D=15.4pm0.6$ Mpc. It is shown that stars in the field located between M86 and M87 galaxies at angular separations of $37^prime$ and $40^prime$ are not intergalactic stars, but belong to the M87 galaxy, i.e., that the stellar halo of this galaxy can be clearly seen at a galactocentric distance of 190 kpc. The distances are measured to four dwarf galaxies P4anon, NGC4486A, VCCA039, and dSph-D07, whose images can be seen in the fields studied. The first three galaxies are M87 satellites, whereas dSph-D07 is located at a greater distance and is a member of the M86 group.
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