The energy spectrum observed by the AGASA experiment and the spatial distribution of the sources of ultra-high energy cosmic rays

Seven and a half years of continuous monitoring of giant air showers triggered by ultra high-energy cosmic rays have been recently summarized by the AGASA collaboration. The resulting energy spectrum indicates clearly that the cosmic ray spectrum extends well beyond the Greisen-Zatsepin-Kuzmin (GZK) cut-off at $\sim 5 \times 10^{19}$ eV. Furthermore, despite the small number statistics involved, some structure in the spectrum may be emerging. Using numerical simulations, it is demonstrated in the present work that these features are consistent with a spatial distribution of sources that follows the distribution of luminous matter in the local Universe. Therefore, from this point of view, there is no need for a second high-energy component of cosmic rays dominating the spectrum beyond the GZK cut-off.Comment: 14 pages, 4 figures, Astrophys. J. Letters (submitted

On the significance of the observed clustering of ultra-high energy cosmic rays

Three pairs of possibly correlated ultra-high energy cosmic ray events were reported by Hayashida et al (1996). Here we calculate the propagation of the corresponding particles through both the intergalactic and galactic magnetic fields. The large scale disc and halo magnetic components are approximated by the models of Stanev (1997). The intergalactic magnetic field intensity is modulated by the actual density of luminous matter along the corresponding lines of sight, calculated from the CfA redshift catalogue (Huchra et al, 1995). The results indicate that, if the events of each pair had a common source and were simultaneously produced, they either originated inside the galactic halo or otherwise very unlikely events were observed. On the other hand, an estimate of the arrival probability of ultra-high energy cosmic rays, under the assumption that the distribution of luminous matter in the nearby universe traces the distribution of the sources of the particles and intensity of the intergalactic magnetic field, suggests that the pairs are chance clusterings.Comment: Ap. J. Letters Accepted - 13 pages + 4 figure

Prospects for direct cosmic ray mass measurements through the Gerasimova-Zatsepin effect

The Solar radiation field may break apart ultra high energy cosmic nuclei, after which both remnants will be deflected in the interplanetary magnetic field in different ways. This process is known as the Gerasimova-Zatsepin effect after its discoverers. We investigate the possibility of using the detection of the separated air showers produced by a pair of remnant particles as a way to identify the species of the original cosmic ray primary directly. Event rates for current and proposed detectors are estimated, and requirements are defined for ideal detectors of this phenomenon. Detailed computational models of the disintegration and deflection processes for a wide range of cosmic ray primaries in the energy range of 10^16 to 10^20 eV are combined with sophisticated detector models to calculate realistic detection rates. The fraction of Gerasimova-Zatsepin events is found to be of the order of 10^-5 of the cosmic ray flux, implying an intrinsic event rate of around 0.07 km^-2 sr^-1 yr^-1 in the energy range defined. Event rates in any real experiment, however, existing or under construction, will probably not exceed 10^-2 yr^-1.Comment: 4 pages, 4 figure

Acceptance of fluorescence detectors and its implication in energy spectrum inference at the highest energies

Along the years HiRes and AGASA experiments have explored the fluorescence and the ground array experimental techniques to measure extensive air showers, being both essential to investigate the ultra-high energy cosmic rays. However, such Collaborations have published contradictory energy spectra for energies above the GZK cut-off. In this article, we investigate the acceptance of fluorescence telescopes to different primary particles at the highest energies. Using CORSIKA and CONEX shower simulations without and with the new pre-showering scheme, which allows photons to interact in the Earth magnetic field, we estimate the aperture of the HiRes-I telescope for gammas, iron nuclei and protons primaries as a function of the number of simulated events and primary energy. We also investigate the possibility that systematic differences in shower development for hadrons and gammas could mask or distort vital features of the cosmic ray energy spectrum at energies above the photo-pion production threshold. The impact of these effects on the true acceptance of a fluorescence detector is analyzed in the context of top-down production models

Impact of electric trucks in GHG inventory – A Uruguayan scenario study

Agencia Nacional de Investigación e Innovación. FSE_1_2019_1_158846. Fondo Sectorial de Energía (Proyecto) – 2019. “Transporte Eléctrico de Carga: Análisis de los desafíos para su introducción en Uruguay”. Duración: octubre 2020 – abril 2022.This paper aims at studying the status of the current fleet of freight vehicles that travel through Uruguay, following international methodologies for calculating GHG gas emissions to determine the current inventory of gases caused by road freight transport. This inventory acts as a starting point to establish three future scenarios where different alternative powertrain technologies are implemented at different rates, such as battery electric vehicles (BEV) and fuel cell electric vehicles (FCEV). The transition from Euro III regulations into Euro V is also considered for these scenarios. Based on these future scenarios, it is possible to project the levels of future emissions that Uruguay will perceive in a time horizon that reaches the year 2050. This study aims to increase the level of information present in the region on the emissions generated in the road freight transport sector, providing new input to the development of future policies on these issues

Fast Synthetic Dataset for Kitchen Object Segmentation in Deep Learning

Object recognition has been widely investigated in computer vision for many years. Currently, this process is carried out through neural networks, but there are very few public datasets available with mask and class labels of the objects for the training process in usual applications. In this paper, we address the problem of fast generation of synthetic datasets to train neural models because creating a handcraft labeled dataset with object segmentation is a very tedious and time-consuming task. We propose an efficient method to generate a synthetic labeled dataset that adequately combines background images with foreground segmented objects. The synthetic images can be created automatically with random positioning of the objects or, alternatively, the method can produce realistic images by keeping the realism in the scales and positions of the objects. Then, we employ Mask-RCNN deep learning model, to detect and segment classes of kitchen objects using images. In the experimental evaluation, we study both synthetic datasets, automatic or realistic, and we compare the results. We analyze the performance with the most widely used indexes and check that the realistic synthetic dataset, quickly created through our method, can provide competitive results and accurately classify the different objects

Decaying neutron propagation in the Galaxy and the Cosmic Ray anisotropy at 1 EeV

We study the cosmic ray arrival distribution expected from a source of neutrons in the galactic center at energies around 1 EeV and compare it with the anisotropy detected by AGASA and SUGAR. Besides the point-like signal in the source direction produced by the direct neutrons, an extended signal due to the protons produced in neutron decays is expected. This associated proton signal also leads to an excess in the direction of the spiral arm. For realistic models of the regular and random galactic magnetic fields, the resulting anisotropy as a function of the energy is obtained. We find that for the anisotropy to become sufficiently suppressed below E\sim 10^{17.9}eV, a significant random magnetic field component is required, while on the other hand, this also tends to increase the angular spread of the associated proton signal and to reduce the excess in the spiral arm direction. The source luminosity required in order that the right ascension anisotropy be 4% for the AGASA angular exposure corresponds to a prediction for the point-like flux from direct neutrons compatible with the flux detected by SUGAR. We also analyse the distinguishing features predicted for a large statistics southern observatory.Comment: 14 pages, 6 figures, minor changes to match published versio

Unmasking the tail of the cosmic ray spectrum

A re-examination of the energy cosmic ray spectrum above $10^{20}$ eV is presented. The overall data-base provides evidence, albeit still statistically limited, that non-nucleon primaries could be present at the end of the spectrum. In particular, the possible appearance of superheavy nuclei (seldom discussed in the literature) is analysed in detail.Comment: To appear in Phys. Lett. B with the title ``Possible explanation for the tail of the cosmic ray spectrum'