1,831,722 research outputs found
Electrons in the cosmic radiation
Get PDFThe nature of cosmic ray electrons and their radiation in the Universe has been studied. A convection associated diffusion model is proposed to describe the main characteristics of the large-scale distribution of cosmic ray electrons in the Galaxy: (1) a small Galacto-centric radial gradient; (2) spectral flattening with Galactic latitude; and (3) an extensive halo above the Disk. A new derivation of the interstellar radiation field indicates the existence of an inverse Compton γ -ray halo. This γ -ray halo can contribute up to 60% of the observed diffuse Galactic γ-ray flux at intermediate latitudes and also accounts for the spectral flattening with latitude. This result leads to a new estimate of the extragalactic γ -ray background flux. An energy equipaxtition theory is proposed for the global correlation between radio power and far-infrared luminosity for spiral galaxies, in which the dynamical role of cosmic rays in galactic evolution is implied. The model successfully explains the non-unity slope of the correlation and predicts the escape of cosmic ray electrons from our Galaxy. The interstellar flux of MeV cosmic ray electrons is derived from γ -ray data. The flux is found to be surprisingly high and a new type of source is required. The lower hybrid plasma instability initiated by stellar winds is suggested to be the acceleration mechanism. This high flux of electrons is sufficient to account for the interstellar ionization and heating in HI regions. Features of the local Galactic magnetic field are revealed by analysing pulsar rotation measure data. The large scale regular field is found to be in a bisymmetric configuration and to be stronger in the interarm region (3 µG) than in the arm region (1 µG). The derived small-scale irregular field is shown to have a dominant strength of 6 µG
Measurement of Ultra-High Energy Cosmic Rays with CHICOS
Get PDFThe California HIgh school Cosmic ray ObServatory (CHICOS) is a ground-based scintillator array designed to measure the extended air showers of ultra-high energy cosmic rays. The goal of the project is to gain insight into the origin of ultra-high energy cosmic rays by measuring the energy spectrum and the distribution of arrival directions.
The CHICOS array has been in operation since 2003. It consists of 77 pairs of scintillator dectectors deployed at schools in the San Fernando and San Gabriel valleys near Los Angeles, and is designed to observe cosmic ray air showers at energies of 10^18 eV and above. In addition, the Chiquita subarray is designed to observe smaller showers in the energy range of 1016 - 1019 eV.
We present new descriptions of the air shower lateral distribution function and time distribution function, which have been derived from AIRES-generated simulated air showers. The new functions are specific to the CHICOS altitude and allow for a maximum likelihood shower reconstruction method, which is more appropriate to the CHICOS data than the χ2 minimization method. We present several analyses of the accuracy of the reconstruction software in the energy ranges available to the Chiquita and CHICOS arrays.
The energy spectrum between 1017 eV and 1019 eV has been measured by the Chiquita subarray. At the lowest energy range, it is found to agree with previous measurements, while the measured flux falls below previous experiments for energies greater than approximately 1017.5 eV. The CHICOS energy spectrum above 1018.4 eV is found to agree with previous results published by AGASA. However, we do not observe the cutoff in the spectrum at 1020 eV reported more recently by the Auger and HiRes Collaborations.
A correlation analysis between CHICOS data and nearby active galactic nuclei (AGN) was performed. No excess of cosmic rays was observed in the vicinity of nearby AGN. The maximum correlation was observed for cosmic ray events with E > 1020 eV and for AGN with z < 0.009, with Pchance = 21%. This is consistent with random correlations from an isotropic distribution, a result also found by HiRes, but in disagreement with Auger.</p
COSMIC-PopSynth/COSMIC: COSMIC -- 08/10/22
No full textSee the changelog for a description of the major changes
Full list of PRs:
kstar hotfix by @katiebreivik in https://github.com/COSMIC-PopSynth/COSMIC/pull/543
correcting the upper end of the pisn gap in the Marchant+ prescription by @michaelzevin in https://github.com/COSMIC-PopSynth/COSMIC/pull/545
Eddfac application for wind accretion in massive stars by @katiebreivik in https://github.com/COSMIC-PopSynth/COSMIC/pull/546
fixed the silly integration errors when sampling a Plummer profile by @carlrodriguez in https://github.com/COSMIC-PopSynth/COSMIC/pull/550
qmin, m2min, msort by @michaelzevin in https://github.com/COSMIC-PopSynth/COSMIC/pull/551
Sse changes by @poojanagrawal in https://github.com/COSMIC-PopSynth/COSMIC/pull/555
This should release pre-built wheels for Python 3.9 and 3.10 by @scottcoughlin2014 in https://github.com/COSMIC-PopSynth/COSMIC/pull/557
Tiny pr that fixes broken docs because of warning by @katiebreivik in https://github.com/COSMIC-PopSynth/COSMIC/pull/559
Orbital sampling by @elenagonzalez870 in https://github.com/COSMIC-PopSynth/COSMIC/pull/563
Fixing gh actions by @scottcoughlin2014 in https://github.com/COSMIC-PopSynth/COSMIC/pull/562
bump python version by @katiebreivik in https://github.com/COSMIC-PopSynth/COSMIC/pull/564
updating ubuntu image by @katiebreivik in https://github.com/COSMIC-PopSynth/COSMIC/pull/565
had wrong name for ubuntu image by @katiebreivik in https://github.com/COSMIC-PopSynth/COSMIC/pull/566
New Contributors
@poojanagrawal made their first contribution in https://github.com/COSMIC-PopSynth/COSMIC/pull/555
@elenagonzalez870 made their first contribution in https://github.com/COSMIC-PopSynth/COSMIC/pull/563
Full Changelog: https://github.com/COSMIC-PopSynth/COSMIC/compare/v3.4.0...v3.4.
The Observational Signatures of Cosmic Strings
No full textCosmic strings were postulated by Kibble in 1976 and, from a theoretical point of view, their existence finds support in modern superstring theories, both in compactification models and in theories with extended additional dimensions. One of the best observational evidences for cosmic strings is the gravitational lensing effects they produce. A first effect is produced by an intervening string along the line of sight which splits in two components (double images) faint background galaxies, thus forming a chain of lensed galaxies along the path of the string. The second optical method is the serendipity discovery through anomalous lensing of extended objects. The huge ratio existing between the string width and length leads to a sort of step function signature on the gravitationally lensed images of background sources. The optical research of cosmic strings signatures suffers from many spurious effects mainly induced by the fact that, in order to be effective, the detection of background galaxies needs to be pushed down to very low flux limits. At these flux levels photometric errors, as well as noise statistics increase the number of spurious detections and, for instance, an application to the Sloan Digital Sky Survey leads to an huge and unrealistic number of candidate pairs. One way to minimize the contamination introduced in the catalogues by the spurious detection, is to increase the contrast by selecting pairs in the 3D space, i.e. by attributing to each galaxy a redshift estimate. At this purpose, a new method for photometric redshifts estimation has been created. The method is based on multiwavelength photometry and on a combination of various data mining techniques developed under the EuroVO and NVO frameworks for data gathering, pre-processing and mining, while relying on the scaling capabilities of the computing grid. This method allowed us to obtain photometric redshifts with an increased accuracy (up to 30%) with respect to the literature. The second fundamental observational evidence for cosmic strings is the signature they are expected to leave in the CMB a signature which may be sought for in the available WMAP data and in the soon to come Planck data. Theory shows that a moving string should produce a step-like discontinuity of low S/N ratio in the CMB, as a consequence of the Doppler shift due to the relative velocity between the string and the observer, thus causing the temperature distribution to deviate from a Gaussian. In the simplifying assumption that the string is a straight discontinuity in space time, we used the S.Co.P.E. computational grid to produce a large number of simulations covering a wide range of values for the velocity of the string, its direction and its distance from the observer. Simulations are produced using a C++ code that generates realistic maps of the CMB temperature distribution in presence of a straight cosmic string. By varying its characteristic parameters, it is possible to explore the signatures left by various types of moving strings. In order to amplify the step-like discontinuity and smooth the noise, maps are then subjected to a “squeezing” procedure. Successively, on the “squeezed” maps, we tested some filters that recognizes high value differences between close pixels. The excellent results of our filter on simulations prompted us to apply it on WMAP 5 years data
COSMIC-PopSynth/COSMIC: COSMIC v3.4.8
No full textWhat's Changed
Nan check by @katiebreivik in https://github.com/COSMIC-PopSynth/COSMIC/pull/576
Remove zsun wind and add NaN catch by @katiebreivik in https://github.com/COSMIC-PopSynth/COSMIC/pull/578
Full Changelog: https://github.com/COSMIC-PopSynth/COSMIC/compare/v3.4.7...v3.4.
COSMIC Brochure and Poster
No full textCOSMIC project will identify the most effective ways in which these new technologies and applications are being used by citizens and governments. The project will also provide instruments for all relevant stakeholders to use new information and communication technologies for the benefit of the security of all citizens
Cosmic strings and scalar tensor gravity
Get PDFThis thesis is concerned with the study of cosmic strings. We studied the values for the Higgs mass and string coupling for which the gravitational effect of an infinite cosmic string in the context of the Einstein theory is not only locally but also globally weak. We conclude this happens for strings formed at scales less or equal to the Planck one with Higgs mass being less or equal to the boson vectorial mass. Then we examined the metric of an isolated self-gravitating abelian-Higgs vortex in dilatonic gravity for arbitrary coupling of the vortex fields to the dilaton. We looked for solutions in both massless and massive dilaton gravity. We compared our results to existing metrics for strings in Einstein and .Jordan-Brans-Dicke theories. We explored the generalisation of Bogomolnyi arguments for our vortices and commented on the effects on test particles. We then included the presence of an axion field and examined the metric of an isolated self-gravitating axionic-dilatonic string. Finally we studied dilatonic strings through black hole solutions in string theory. We concluded that the horizon of non-extreme charged black holes supports the long-range fields of the Nielsen-Olesen string that can be considered as black hole hair and whose gravitational effect is in general the production of a conical deficit into the metric of the black hole background. We also concluded that the effect of the dilaton on the horizon of these black holes is to generate an additional charge
20. COSMIC RAYS
No full textThe cosmic radiation incident at the top of the terrestrial atmosphere includes all stable charged particles and nuclei with lifetimes of order 106 years or longer. Technically, “primary ” cosmic rays are those particles accelerated at astrophysical sources and “secondaries ” are those particles produced in interaction of the primaries with interstellar gas. Thus electrons, protons and helium, as well as carbon, oxygen, iron, and other nuclei synthesized in stars, are primaries. Nuclei such as lithium, beryllium, and boron (which are not abundant end-products of stellar nucleosynthesis) are secondaries. Antiprotons and positrons are partly, if not entirely, secondaries, but the fraction of these particles that may be primary is a question of current interest. Apart from particles associated with solar flares, the cosmic radiation comes from outside the solar system. The incoming charged particles are “modulated ” by the solar wind, the expanding magnetized plasma generated by the Sun, which decelerates and partially excludes the lower energy galactic cosmic rays from the inner solar system. There is a significant anticorrelation between solar activity (which has an eleven-year cycle) and the intensity of the cosmic rays with energies below about 10 GeV. In addition
Jupiter as a giant cosmic ray detector
No full textAll authors highlight financial support of the European Community under the FP7 by an ERC starting grant.We explore the feasibility of using the atmosphere of Jupiter to detect ultra-high-energy cosmic rays (UHECRs). The large surface area of Jupiter allows us to probe cosmic rays of higher energies than previously accessible. Cosmic ray extensive air showers in Jupiter's atmosphere could in principle be detected by the Large Area Telescope (LAT) on the Fermi observatory. In order to be observed, these air showers would need to be oriented toward the Earth, and would need to occur sufficiently high in the atmosphere that the gamma rays can penetrate. We demonstrate that, under these assumptions, Jupiter provides an effective cosmic ray "detector" area of 3.3 × 107 km2. We predict that Fermi-LAT should be able to detect events of energy >1021 eV with fluence 10-7 erg cm-2 at a rate of about one per month. The observed number of air showers may provide an indirect measure of the flux of cosmic rays ≳ 1020 eV. Extensive air showers also produce a synchrotron signature that may be measurable by Atacama Large Millimeter/submillimeter Array (ALMA). Simultaneous observations of Jupiter with ALMA and Fermi-LAT could be used to provide broad constraints on the energies of the initiating cosmic rays.Peer reviewe
Stand-alone cosmic muon reconstruction before installation of the CMS silicon strip tracker
Get PDFThis is the Pre-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2009 IOPThe subsystems of the CMS silicon strip tracker were integrated and commissioned at the Tracker Integration Facility (TIF) in the period from November 2006 to July 2007. As part of the commissioning, large samples of cosmic ray data were recorded under various running conditions in the absence of a magnetic field. Cosmic rays detected by scintillation counters were used to trigger the readout of up to 15 % of the final silicon strip detector, and over 4.7 million events were recorded. This document describes the cosmic track reconstruction and presents results on the performance of track and hit reconstruction as from dedicated analyses.This work was supported by: the Austrian
Federal Ministry of Science and Research; the Belgium Fonds de la Recherche Scientifique and Fonds voorWetenschappelijk
Onderzoek; the Academy of Finland and Helsinki Institute of Physics; the Institut National de Physique Nucleaire et de Physique des Particules / CNRS, France; the Bundesministerium fur Bildung und Forschung, Germany; the Istituto Nazionale di Fisica Nucleare, Italy; the Swiss Funding Agencies; the Science and Technology Facilities Council, UK; the US Department of Energy, and National Science Foundation. Individuals have received support from the Marie-Curie IEF program (European Union) and the A.P. Sloan Foundation
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