G. Medina-Tanco

Origin of the highest energy cosmic rays

Abstract Introducing a simple Galactic wind model patterned after the solar wind we show that back-tracing the orbits of the highest energy cosmic events suggests that they may all come from the Virgo cluster, and so probably from the active radio galaxy M87. This confirms a long standing expectation. Those powerful radio galaxies that have their relativistic jets stuck in the interstellar medium of the host galaxy, such as 3C147, will then enable us to derive limits on the production of any new kind of particle, expected in some extensions of the standard model in particle physics. New data from HIRES will be crucial in testing the model proposed here.

On the Ongoing Multiple Blowout in NGC 604

Several facts regarding the structure of NGC 604 are examined here. The three main cavities produced by the mechanical energy from massive stars, which in NGC 604 are spread over a volume of 106 pc3, are shown here to be undergoing blowout into the halo of M33. High-resolution long-slit spectroscopy is used to track the impact from massive stars, while Hubble Space Telescope archive data are used to display the asymmetry of the nebula. NGC 604 is found to be a collection of photoionized filaments and sections of shells that are in direct contact with the thermalized matter ejected by the massive stars. The multiple blowout events presently drain the energy injected by massive stars, and thus the densest photoionized gas is found almost at rest and is expected to suffer a slow evolution.

The JEM-EUSO Mission

The JEM‐EUSO mission explores the origin of the extreme energy cosmic rays (EECRs) above 100 EeV and explores the limits of the fundamental physics, through the observations of their arrival directions and energies. It is designed to achieve an exposure larger than 1 million km2 sr year at the highest energies to open a new particle astronomy channel. This super‐wide‐field of view (60 degrees) telescope with a diameter of about 2.5 m looks down from space onto the night sky to detect near UV photons (330–400 nm, both fluorescent and Cherenkov photons) emitted from the giant air showers produced by EECRs. The arrival direction map with more than five hundred events after just the three years will tell us the origin of the EECRs, allow us to identify the nearest EECR sources with known astronomical objects, which can afterwards be examined in other astronomical channels. This is likely to lead to an understanding of the acceleration mechanisms perhaps producing discoveries in astrophysics and fundamental ph...

A new composition-sensitive parameter for ultra-high energy cosmic rays

Abstract A new family of parameters intended for composition studies in cosmic ray surface array detectors is proposed. The application of this technique to different array layout designs has been analyzed. The parameters make exclusive use of surface data combining the information from the total signal at each triggered detector and the array geometry. They are sensitive to the combined effects of the different muon and electromagnetic components on the lateral distribution function of proton and iron initiated showers at any given primary energy. Analytical and numerical studies have been performed in order to assess the reliability, stability and optimization of these parameters. Experimental uncertainties, the underestimation of the muon component in the shower simulation codes, intrinsic fluctuations and reconstruction errors are considered and discussed in a quantitative way. The potential discrimination power of these parameters, under realistic experimental conditions, is compared on a simplified, albeit quantitative way, with that expected from other surface and fluorescence estimators.

On the formation of massive stellar clusters

Here we report on the properties of the star forming factory, in which the continuous creation of stars results into a highly concentrated, massive (globular cluster-like) stellar system. We show that under very general conditions a large-scale gravitational instability in the ISM, that triggers the collapse of a massive cloud, leads with the aid of a spontaneous rst generation of massive stars, to a standing, small radius, cold and dense shell. Eventually, as more of the collapsing matter is processed and incorporated, the shell becomes gravitationally unstable and begins to fragment, allowing for the formation of new stars. The shell keeps its standing location thanks to a detailed balance established between the ram pressure from the collapsing cloud which, together with the gravitational force excerted on the shell by the forming cluster, act against the mechanical energy deposited by the collection of new stars. The model accounts for a full analysis of feedback, as well as for the mass spectrum of fragments that result from the continuous fragmentation of the standing shell. This matches well, at both ends of the spectrum, the properties of a universal IMF. Other properties of the modelled clusters are here stressed.

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 summarized recently by the AGASA collaboration. The resulting energy spectrum indicates clearly that the cosmic-ray spectrum extends well beyond the Greisen-Zatsepin-Kuzmin (GZK) cutoff at ~5 × 1019 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 cutoff.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 ∼ 5 × 10 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. Subject headings: Cosmic Rays — large-scale structure — magnetic fields

Perturbative exponential expansion and matter neutrino oscillations

We derive an analytical description of neutrino oscillations in matter based on the Magnus exponential representation of the time evolution operator. Our approach is valid in a wide range of the neutrino energies and properly accounts for the modifications that the respective probability transitions suffer when neutrinos originated in different sources traverse the Earth. The present approximation considerably improves over other perturbative treatments existing in the current literature. Furthermore, the analytical expressions derived inside the Magnus framework are remarkably simple, which facilitates their practical use. When applied to the calculation of the day-night asymmetry in the solar neutrino flux our result reproduces the numerical calculation with an accuracy better than 1% for the first-order approximation. When the approximation is extended to the second order, the accuracy of the method is further improved by almost 1 order of magnitude, and it is still better than 5% even for neutrino energies as large as 100 MeV. In the GeV regime characteristic of atmospheric and accelerator neutrinos this accuracy is complemented by a good reproduction of the position of the maxima in the flavor transition probabilities.

Longitudinal development of extensive air showers: Hybrid code SENECA and full Monte Carlo

Abstract New experiments, exploring the ultra-high energy tail of the cosmic ray spectrum with unprecedented detail, are exerting a severe pressure on extensive air shower modelling. Detailed fast codes are in need in order to extract and understand the richness of information now available. Some hybrid simulation codes have been proposed recently to this effect (e.g., the combination of the traditional Monte Carlo scheme and system of cascade equations or pre-simulated air showers). In this context, we explore the potential of SENECA, an efficient hybrid tri-dimensional simulation code, as a valid practical alternative to full Monte Carlo simulations of extensive air showers generated by ultra-high energy cosmic rays. We extensively compare hybrid method with the traditional, but time consuming, full Monte Carlo code CORSIKA which is the de facto standard in the field. The hybrid scheme of the SENECA code is based on the simulation of each particle with the traditional Monte Carlo method at two steps of the shower development: the first step predicts the large fluctuations in the very first particle interactions at high energies while the second step provides a well detailed lateral distribution simulation of the final stages of the air shower. Both Monte Carlo simulation steps are connected by a cascade equation system which reproduces correctly the hadronic and electromagnetic longitudinal profile. We study the influence of this approach on the main longitudinal characteristics of proton, iron nucleus and gamma induced air showers and compare the predictions of the well known CORSIKA code using the QGSJET hadronic interaction model.

Ultra-High Energy Cosmic Rays: Are They Isotropic?

From the analysis of Akeno Giant Air Shower Array (AGASA) data above 4 × 1019 eV, we show that the ultra-high energy cosmic ray flux is neither purely isotropic nor reflects the expected anisotropy from a pure source distribution that maps large-scale structure in the local universe. The arrival distribution seems to be the result of a mixture of fluxes (e.g., dark matter halo plus large-scale structure) or the superposition of direct and diffuse radiation field components, respectively. Another viable option is an arbitrary extragalactic flux reprocessed by a magnetized galactic wind model, as recently proposed in the literature.

Overall View of the JEM‐EUSO Instruments

JEM‐EUSO mission with a large and wide‐angle telescope mounted on ISS has been planned to open up “particle astronomy” through the investigation of extreme‐energy cosmic rays by detecting fluorescent and Cherenkov photons by air showers developed in the earth’s atmosphere. The JEM‐EUSO telescope consists of optical Fresnel lenses with a diameter of about 2.5 m, 300 k channels of MAPMT, frontend readout electronics, trigger electronics, and system electronics. An infrared camera and a LIDAR system will be used to monitor the earth’s atmosphere.