How isotropic can the UHECR flux be?

Modern observatories of ultra-high energy cosmic rays (UHECR) have collected over 10^4 events with energies above 10 EeV, whose arrival directions appear to be nearly isotropically distributed. On the other hand, the distribution of matter in the nearby Universe -- and, therefore, presumably also that of UHECR sources -- is not homogeneous. This is expected to leave an imprint on the angular distribution of UHECR arrival directions, though deflections by cosmic magnetic fields can confound the picture. In this work, we investigate quantitatively this apparent inconsistency. To this end we study observables sensitive to UHECR source inhomogeneities but robust to uncertainties on magnetic fields and the UHECR mass composition. We show, in a rather model-independent way, that if the source distribution tracks the overall matter distribution, the arrival directions at energies above 30 EeV should exhibit a sizeable dipole and quadrupole anisotropy, detectable by UHECR observatories in the very near future. Were it not the case, one would have to seriously reconsider the present understanding of cosmic magnetic fields and/or the UHECR composition. Also, we show that the lack of a strong quadrupole moment above 10 EeV in the current data already disfavours a pure proton composition, and that in the very near future measurements of the dipole and quadrupole moment above 60 EeV will be able to provide evidence about the UHECR mass composition at those energies.Comment: 9 pages, 8 figures; accepted versio

Propagation of high-energy cosmic rays in extragalactic turbulent magnetic fields: resulting energy spectrum and composition

We extend previous studies of mixed-composition extragalactic cosmic-ray source models, by investigating the influence of a non-negligible extragalactic magnetic field on the propagated cosmic-ray spectrum and composition. We study the transport of charged particles in turbulent fields and the transition from a ballistic to a diffusive propagation regime. We introduce a method allowing a fast integration of the particle trajectories, which allows us to calculate extragalactic cosmic-ray spectra in the general case, without using either the diffusive or the rectilinear approximation. We find that the main features of the mixed-composition models -- regarding the interpretation of the ankle and the non-monotonous evolution of the average cosmic-ray mass -- remain essentially unchanged as long as the magnetic field intensity does not exceed a few nG.Comment: 15 pages, 20 figure

Fernand Deligny: pedagogia y nomadismo en la educación de las "otras infancias"

L'article revisa la vida i l'obra de l'educador francès Fernand Deligny i ho fa des de la perspectiva de les altres infàncies, de les que han oblidades per les pedagogies «generals». Des d'una posició que hem anomenat «pedagogía nòmada» (per la seva mobilitat intel·lectual però també per la seva transhumància social) el treball ofereix diferents temàtiques que permeten analitzar, des d'una posició micro, els elements que configuren la basta obra del controvertit educador.The article reviews the life and work of the French educator Fernand Deligny, and does so from the perspective of other childhoods, from the ones that have been forgotten by «general» pedagogies. From a point of view that we have called «nomadic pedagogy» (due to its intellectual mobility and also to its social transhumance) the work offers different issues that enable –from a micro approach– an analysis of the elements that make up the vast work of the controversial educator.El artículo revisa la vida y la obra del educador francés Fernand Deligny y no hace desde la perspectiva de las otras infancias, de las que han sido descuidadas o son olvidadas por las pedagogías «generales». Des de una posición que hemos denominado «pedagogía nómada» (por su movilidad intelectual pero también por su trashumancia social) el trabajo ofrece diferentes temáticas que permiten analizar, desde una posición micro, los elementos que configuran la basta obra del controvertido educador

Fernand Deligny’s autists: In favor of an impolitical education

Nuestro trabajo será una lectura de lo impolítico y lo imposible que nos lega Deligny, haciendo foco en las traducciones al castellano de Los Vagabundos Eficaces (1971) y Lo Arácnido y otros textos (2015). Retomaremos «lo impolítico» de la filosofía de Esposito y lo aplicaremos al ejercicio del desencuadre en Deligny. Recorreremos tres encuadres modernos: sujeto, proyecto, rendimiento; a cada uno de ellos le presentaremos un rasgo de Deligny: autista, arácnido, vagabundos eficaces. A lo largo de todos ellos intentaremos mostrar la comunidad autista de Deligny como acto impolítico a la educación moderna. Finalmente, nuestra apuesta será por una educación imposible, crítica radical a la representación modernaWe will try to read the concept of impolitic and impossible in Deligny’s work. We will focus on Les Vagabonds Efficaces (“The Efficient Vagabonds”, 1971) and The Arachnean and Other Texts (2015). We will return to “the impolitic” of Esposito’s philosophy and try to apply it to the exercise of unframing in Deligny. We will work on three great modern frames: subject, project, achievement; to each of them, we will present a trait of Delig-ny: autistic, arachnid, effective vagabonds. Throughout them, we will try to show the autistic community of Deligny as an impolitic act to modern education. Finally, our bet will be for an impossible education, a radical critic to modern representatio

The Small Contribution of Molecular Bremsstrahlung Radiation to the Air-Fluorescence Yield of Cosmic Ray Shower Particles

A small contribution of molecular Bremsstrahlung radiation to the air-fluorescence yield in the UV range is estimated based on an approach previously developed in the framework of the radio-detection of showers in the gigahertz frequency range. First, this approach is shown to provide an estimate of the main contribution of the fluorescence yield due to the de-excitation of the C $^3\Pi_{\mathrm{u}}$ electronic level of nitrogen molecules to the B $^3\Pi_{\mathrm{g}}$ one amounting to $Y_{[337]}=(6.05\pm 1.50)~$ MeV$^{-1}$ at 800 hPa pressure and 293 K temperature conditions, which compares well to previous dedicated works and to experimental results. Then, under the same pressure and temperature conditions, the fluorescence yield induced by molecular Bremsstrahlung radiation is found to be $Y_{[330-400]}^{\mathrm{MBR}}=0.10~$ MeV$^{-1}$ in the wavelength range of interest for the air-fluorescence detectors used to detect extensive air showers induced in the atmosphere by ultra-high energy cosmic rays. This means that out of $\simeq 175~$ photons with wavelength between 330 and 400 nm detected by fluorescence detectors, one of them has been produced by molecular Bremsstrahlung radiation. Although small, this contribution is not negligible in regards to the total budget of systematic uncertainties when considering the absolute energy scale of fluorescence detectors.Comment: 9 pages, 2 figures, accepted for publication in Astropart. Phys. arXiv admin note: text overlap with arXiv:1601.0055

UHE nuclei propagation and the interpretation of the ankle in the cosmic-ray spectrum

We consider the stochastic propagation of high-energy protons and nuclei in the cosmological microwave and infrared backgrounds, using revised photonuclear cross-sections and following primary and secondary nuclei in the full 2D nuclear chart. We confirm earlier results showing that the high-energy data can be fit with a pure proton extragalactic cosmic ray (EGCR) component if the source spectrum is \propto E^{-2.6}. In this case the ankle in the CR spectrum may be interpreted as a pair-production dip associated with the propagation. We show that when heavier nuclei are included in the source with a composition similar to that of Galactic cosmic-rays (GCRs), the pair-production dip is not present unless the proton fraction is higher than 85%. In the mixed composition case, the ankle recovers the past interpretation as the transition from GCRs to EGCRs and the highest energy data can be explained by a harder source spectrum \propto E^{-2.2} - E^{-2.3}, reminiscent of relativistic shock acceleration predictions, and in good agreement with the GCR data at low-energy and holistic scenarios.Comment: 4 pages, 4 figures, submitted to A&A Letters (minor changes, two figures replaced, two references added

On the viability of holistic cosmic-ray source models

We consider the energy spectrum of cosmic-rays (CRs) from a purely phenomenological point of view and investigate the possibility that they all be produced by the same type of sources with a single power-law spectrum, in E^{-x}, from thermal to ultra-high energies. We show that the relative fluxes of the Galactic (GCR) and extra-galactic (EGCR) components are compatible with such a holistic model, provided that the index of the source spectrum be x \simeq 2.23\pm 0.07. This is compatible with the best-fit indices for both GCRs and EGCRs, assuming that their source composition is the same, which is indeed the case in a holistic model. It is also compatible with theoretical expectations for particle acceleration at relativistic shocks.Comment: 5 pages, 1 figure, Accepted for publication in Astronomy and Astrophysic