Ray Space Research Articles

Variatsii kosmicheskikh luchei i kosmicheskaya pogoda

Variatsii kosmicheskikh luchei i kosmicheskaya pogoda

On energetic particles in space

On energetic particles in spaceParticles energized above the Earth's atmosphere provide unique informations about specific physical processes in the outer space. This is an attempt to present a short review of the knowledge of the characteristics of the cosmic energetic particles in wide energy range as observed on the ground, in the atmosphere, on Earth's satellites and on space probes. However, the review is related only to selected problems of cosmic ray physics and space physics. The bias is especially towards lower energies. After the historical introduction the features of primary cosmic rays is described. The heliosphere, in which the direct measurements of cosmic energetic particles takes place, is modulating the primary flux by magnetic fields controlled by the processes on solar surface and, is contributing to the low energy population by acceleration via transient processes as well as by solar flares. Important processes occur near the heliospheric outer boundary from where recently the space probes provided new information. Heliospheric influence is summarized in the third chapter. Another important object, the magnetosphere, is changing trajectories of incoming charged particles by "magnetospheric optics". Magnetosphere iself by the acceleration, transport, trapping as well as losses of lower energy particles alternates significantly the radiation environment near the Earth. The knowledge of particle population for which the condition of trapping are suitable in magnetospheres of giant planets of solar system, have increased thanks to space probes and planetary orbiters. Chapter four summarizes few important points of the magnetospheric influence on energetic particles. The measurements of temporal variability of the flux, energy spectra and angular distribution of cosmic ray particles influenced by solar-terrestrial effects, provides a unique tool for monitoring and eventual prediction of space weather effects, in addition to the investigations of the photon flux of various wavelength from the Sun, solar wind plasma and the magnetic field in interplanetary space. This is the main part of the chapter five.

Indirect searches in the PAMELA and Fermi era

The detection of γ -rays, antiprotons and positrons due to pair annihilation of dark matter particles in the Milky Way halo is a viable indirect technique to search for signatures of supersymmetric dark matter where the major challenge is the discrimination of the signal from the background generated by standard production mechanisms. The new PAMELA antiproton data are consistent with the standard secondary production and this allows us to constrain exotic contribution to the spectrum due to neutralino annihilations. In particular, we show that in the framework of minimal supergravity (mSUGRA), in a clumpy halo scenario (with clumpiness factor ⩾10) and for large values of tan ( β ) ⩾ 55 , almost all the parameter space allowed by WMAP is excluded. Instead the PAMELA positron fraction data exhibit an excess that it is very difficult to explain with secondary production. The Fermi-LAT experiment recently reported high precision measurements of the spectrum of cosmicray electrons-plus-positrons (CRE) between 20 GeV and 1 TeV. The spectrum shows no prominent spectral features, and is significantly harder than that inferred from several previous experiments. The PAMELA excess in positron fraction combined with the new Fermi results on the electron+positron spectrum unavoidably testifies the presence of primary positrons in cosmic rays because it is not possible to explain the PAMELA ratio with a deficit of electrons at high energies. Here we discuss the status of indirect dark matter searches and a perspective for PAMELA and Fermi γ -ray space telescope experiments.

How dark matter reionized the Universe

Although empirical evidence indicates that the Universe's gas had become ionized by redshift z{approx_equal}6, the mechanism by which this transition occurred remains unclear. In this article, we explore the possibility that dark matter annihilations may have played the dominant role in this process. Energetic electrons produced in these annihilations can scatter with the cosmic microwave background to generate relatively low energy gamma rays, which ionize and heat gas far more efficiently than higher energy prompt photons. In contrast to previous studies, we find that viable dark matter candidates with electroweak scale masses can naturally provide the dominant contribution to the reionization of the Universe. Intriguingly, we find that dark matter candidates capable of producing the recent cosmic ray positron excesses observed by PAMELA (or the electrons spectrum measured by the Fermi Gamma Ray Space Telescope) are also predicted to lead to the full reionization of the Universe by z{approx}6.

GAMMA-RAY BURST PREDICTIONS FOR THEFERMI GAMMA RAY SPACE TELESCOPE

Results of a phenomenological model to estimate the GRB detection rate by the Fermi Gamma ray Space Telescope are reported. This estimate is based on the BATSE 4B GRB fluence distribution, the mean ratio of fluences measured at 100 MeV - 5 GeV with EGRET and at 20 keV - 2 MeV with BATSE, and the mean EGRET GRB spectrum for the 5 EGRET spark-chamber GRBs. For a 10% fluence ratio and a number spectral index alpha_1 = -2 at 100 MeV - 5 GeV energies, we estimate a rate of ~ 20 and 4 GRBs per yr in the Fermi Large Area Telescope field of view with at least 5 photons with energy E > 100 MeV and E > 1 GeV, respectively. We also estimate ~ 1.5 GRBs per yr in the Fermi FoV where at least 1 photon with energy E > 10 GeV is detected. For these parameters, we estimate = 1 - 2 GRBs per year detected with the Fermi telescope with more than 100 gamma rays with E >~ 100$ MeV. Comparison predictions for alpha_1 = -2.2, different fluence ratios, and the AGILE gamma-ray satellite are made. Searches for different classes of GRBs using a diagram plotting 100 MeV - 10 GeV fluence vs. 20 keV - 20 MeV fluence is considered as a way to search for separate classes of GRBs and, specifically, spectral differences between the short-hard and long duration GRB classes, and for hard components in GRBs.

BRIGHT ACTIVE GALACTIC NUCLEI SOURCE LIST FROM THE FIRST THREE MONTHS OF THEFERMILARGE AREA TELESCOPE ALL-SKY SURVEY

The first three months of sky-survey operation with the Fermi Gamma Ray Space Telescope (Fermi) Large Area Telescope (LAT) reveals 132 bright sources at |b|>10 deg with test statistic greater than 100 (corresponding to about 10 sigma). Two methods, based on the CGRaBS, CRATES and BZCat catalogs, indicate high-confidence associations of 106 of these sources with known AGNs. This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely Centaurus A and NGC 1275, and 104 blazars consisting of 57 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and 5 blazars with uncertain classification. Four new blazars were discovered on the basis of the LAT detections. Remarkably, the LBAS includes 10 high-energy peaked BL Lacs (HBLs), sources which were so far hard to detect in the GeV range. Another 10 lower-confidence associations are found. Only thirty three of the sources, plus two at |b|>10 deg, were previously detected with EGRET, probably due to the variable nature of these sources. The analysis of the gamma-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. No significant correlation between radio and peak gamma-ray fluxes is observed. Blazar log N - log S and luminosity functions are constructed to investigate the evolution of the different blazar classes, with positive evolution indicated for FSRQs but none for BLLacs. The contribution of LAT-blazars to the total extragalactic gamma-ray intensity is estimated.

FERMIDISCOVERY OF GAMMA-RAY EMISSION FROM NGC 1275

We report the discovery of high-energy (E>100 MeV) gamma-ray emission from NGC 1275, a giant elliptical galaxy lying at the center of the Perseus cluster of galaxies, based on observations made with the Large Area Telescope (LAT) of the Fermi Gamma ray Space Telescope. The positional center of the gamma-ray source is only ~3' away from the NGC 1275 nucleus, well within the 95% LAT error circle of ~5'.The spatial distribution of gamma-ray photons is consistent with a point source. The average flux and power-law photon index measured with the LAT from 2008 August 4 to 2008 December 5 are F_gamma = (2.10+-0.23)x 10^{-7} ph (>100 MeV) cm^{-2} s^{-1} and Gamma = 2.17+-0.05, respectively. The measurements are statistically consistent with constant flux during the four-month LAT observing period.Previous EGRET observations gave an upper limit of F_gamma < 3.72x 10 ^{-8} ph (>100 MeV) cm^{-2} s^{-1} to the gamma-ray flux from NGC 1275. This indicates that the source is variable on timescales of years to decades, and therefore restricts the fraction of emission that can be produced in extended regions of the galaxy cluster. Contemporaneous and historical radio observations are also reported. The broadband spectrum of NGC 1275 is modeled with a simple one-zone synchrotron/synchrotron self-Compton model and a model with a decelerating jet flow.

THE STELLAR CONTRIBUTION TO THE EXTRAGALACTIC BACKGROUND LIGHT AND ABSORPTION OF HIGH-ENERGY GAMMA RAYS

TeV γ-rays from distant astrophysical sources are attenuated due to electron–positron pair creation by interacting with ultraviolet/optical to infrared photons which fill the universe and are collectively known as the extragalactic background light (EBL). We model the ∼0.1–10 eV starlight component of the EBL derived from expressions for the stellar initial mass function (IMF), star formation history of the universe, and wavelength-dependent absorption of a large sample of galaxies in the local universe. These models are simultaneously fitted to the EBL data as well as to the data on the stellar luminosity density in our local universe. We find that the models with modified Salpeter A IMF together with Cole et al. or Hopkins and Beacom star formation history best represent available data. Since no dust emission is included, our calculated EBL models can be interpreted as the lower limits in the ∼0.1–1 eV range. We present simple analytic fits to the best-fit EBL model evolving with redshift. We then proceed to calculate γ-ray opacities and absorption of ∼10–300 GeV γ-rays coming from different redshifts. We discuss implications of our results for the Fermi Gamma Ray Space Telescope and ground-based Air Cherenkov Telescopes.

GeV telescopes: results and prospects for Fermi

We present a review of the current status and future prospects of the field of high-energy gamma-ray astrophysics in the 30 MeV to 30 GeV regime. Scientific studies in this energy range are carried out by satellite-based gamma-ray instruments. We have now entered a new era in space-based gamma-ray astrophysics with the operation of AGILE and the Fermi Gamma Ray Space Telescope. We summarize here highlights from earlier experiments such as the EGRET on board the Compton Gamma Ray Observatory and describe some of the first results from AGILE and Fermi.

The $so(d + 2, 2)$ minimal representation and ambient tractors: the conformal geometry of momentum space

Tractor Calculus is a powerful tool for analyzing Weyl invariance; although fundamentally linked to the Cartan connection, it may also be arrived at geometrically by viewing a conformal manifold as the space of null rays in a Lorentzian ambient space. For dimension d conformally flat manifolds we show that the (d+2)-dimensional Fefferman--Graham ambient space corresponds to the momentum space of a massless scalar field. Hence on the one hand the null cone parameterizes physical momentum excitations, while on the other hand, null rays correspond to points in the underlying conformal manifold. This allows us to identify a fundamental set of tractor operators with the generators of conformal symmetries of a scalar field theory in a momentum representation. Moreover, these constitute the minimal representation of the non-compact conformal Lie symmetry algebra of the scalar field with Kostant--Kirillov dimension d+1. Relaxing the conformally flat requirement, we find that while the conformal Lie algebra of tractor operators is deformed by curvature corrections, higher relations in the enveloping algebra corresponding to the minimal representation persist. We also discuss potential applications of these results to physics and conformal geometry.

High energy neutron and pion-decay gamma-ray emissions from solar flares

Solar flare gamma-ray emissions from energetic ions and electrons have been detected and measured to GeV energies since 1980. In addition, neutrons produced in solar flares with 100 MeV to GeV energies have been observed at the Earth. These emissions are produced by the highest energy ions and electrons accelerated at the Sun and they provide our only direct (albeit secondary) knowledge about the properties of the accelerator(s) acting in a solar flare. The solar flares, which have direct evidence for pion-decay gamma-rays, are unique and are the focus of this paper. We review our current knowledge of the highest energy solar emissions, and how the characteristics of the acceleration process are deduced from the observations. Results from the RHESSI, INTEGRAL and CORONAS missions will also be covered. The review will also cover the solar flare capabilities of the new mission, FERMI GAMMA RAY SPACE TELESCOPE, launched on 2008 June 11. Finally, we discuss the requirements for future missions to advance this vital area of solar flare physics.

Projective dynamics and classical gravitation

Given a real vector space V of finite dimension, together with a particular homogeneous field of bivectors that we call a "field of projective forces", we define a law of dynamics such that the position of the particle is a "ray" i.e. a half-line drawn from the origin of V. The impulsion is a bivector whose support is a 2-plane containing the ray. Throwing the particle with a given initial impulsion defines a projective trajectory. It is a curve in the space of rays S(V), together with an impulsion attached to each ray. In the simplest example where the force is identically zero, the curve is a straight line and the impulsion a constant bivector. A striking feature of projective dynamics appears: the trajectories are not parameterized. Among the projective force fields corresponding to a central force, the one defining the Kepler problem is simpler than those corresponding to other homogeneities. Here the thrown ray describes a quadratic cone whose section by a hyperplane corresponds to a Keplerian conic. An original point of view on the hidden symmetries of the Kepler problem emerges, and clarifies some remarks due to Halphen and Appell. We also get the unexpected conclusion that there exists a notion of divergence-free field of projective forces if and only if dim V=4. No metric is involved in the axioms of projective dynamics.

Pancharatnam geometric phase originating from successive partial projections

The spin of a polarized neutron beam subjected to a partial projection in another direction, traces a geodesic arc in the 2-sphere ray space. We delineate the geometric phase resulting from two successive partial projections on a general quantal state and derive the direction and strength of the third partial projection that would close the geodesic triangle. The constraint for the three successive partial projections to be identically equivalent to a net spin rotation regardless of the initial state, is derived.

Whole Core Transport Calculation Employing Hexagonal Modular Ray Tracing and CMFD Formulation

A whole core transport module for hexagonal cores is developed and implemented in the DeCART code. The module consists of a whole core ray tracing kernel for solving the two-dimensional (2-D) method of characteristics (MOC) equation and a coarse-mesh finite difference (CMFD) kernel to accelerate the MOC transport iteration. Whole core ray tracing is realized by incorporating a hexagonal-assembly-based modular ray tracing scheme. The complete path linking constraint forthe modular ray is achieved by adjusting the ray angle and the ray spacing in the range of [0, 30°], and the complete reflection constraint at the problem boundary is satisfied by defining the corresponding reflection angles at the reflection surfaces. The hexagonal CMFD kernel employs unstructured nodes that can treat the irregular-shaped gap cells as well as the regular hexagonal cells. Some features such as cell ray approximation and modified cycle ray scheme are employed to reduce the memory requirements for the segment information and the boundary angular fluxes, respectively. The solution accuracy and execution performance of the hexagonal module are examined for the C5G7 hexagonal variation problems that are established by modifying the original C5G7MOX 3-D extension benchmark. The CMFD kernel shows a significant speedup of 60 in the 2-D core problem. The cell ray approximation does not violate the original solution accuracy when using the default ray spacing of the DeCART code. The modified cycle ray scheme shows its superiority over the simple core ray sweeping scheme in terms of the memory requirement and the original cycle ray scheme in terms of the computing time. Compared with the Monte Carlo solutions, the DeCART solution agrees to within 40 pcm for the eigenvalue and 2% for the pin power distribution.

Global Illumination using Photon Ray Splatting

Abstract We present a novel framework for efficiently computing the indirect illumination in diffuse and moderately glossy scenes using density estimation techniques. Many existing global illumination approaches either quickly compute an overly approximate solution or perform an orders of magnitude slower computation to obtain high‐quality results for the indirect illumination. The proposed method improves photon density estimation and leads to significantly better visual quality in particular for complex geometry, while only slightly increasing the computation time. We perform direct splatting of photon rays, which allows us to use simpler search data structures. Since our density estimation is carried out in ray space rather than on surfaces, as in the commonly used photon mapping algorithm, the results are more robust against geometrically incurred sources of bias. This holds also in combination with final gathering where photon mapping often overestimates the illumination near concave geometric features. In addition, we show that our photon splatting technique can be extended to handle moderately glossy surfaces and can be combined with traditional irradiance caching for sparse sampling and filtering in image space.

Ray space ‘Riccati’ evolution and geometric phases for N-level quantum systems

We present a simple derivation of the matrix Riccati equations governing the reduced dynamics as one descends from the group U(N) describing the Schroedinger evolution of an N-level quantum system to the various coset spaces, Grassmanian manifolds, associated with it. The special case pertaining to the geometric phase in N-level systems is described in detail. Further, we show how the matrix Riccati equation thus obtained can be reformulated as an equation describing Hamiltonian evolution in a classical phase space and establish correspondences between the two descriptions.

A study of an air medium influence on the rectilinearity of laser ray proliferation towards the using for large distances and high-precision metrology

The influence of a turbulent air medium on a laser beam space localization precision was studied experimentally. For a helium-neon one-mode laser LGN-302 and for a solid-state multimode laser DS-670, the laser ray coordinate measurement uncertainties were determined with 1 m step for the distances up to 9 m from the laser source. It was found that the σ values at 9 m distance are equal to σ(DS-670) = 21 μm and σ(LGN-302) = 12 μm. To reduce the turbulent air medium influence on the laser ray space localization precision, the laser beam was positioned inside a heat-isolating tube. Very significant decrease of σ values was achieved at 9 m from the source: σ*(DS-670) = 2 μm and σ*(LGN-302) = 2.5 μm. The work is made within a framework of a preparation to the creation of a high-precision large-distance laser metrology to be possibly used for long linear collider component alignment.

1P1-J07 奥行き成分を利用した密な光線空間についての考察(3次元計測/センサフュージョン)

This paper proposes a construction method of dense ray space using depth components. Light Field Rendering is the technology that can compose a free viewpoint image. However, there is a weak point in Light Field Rendering. A high-resolution free viewpoint image needs dense ray space. This construction method supplements a weak point of Light Field Rendering that many cameras are necessary. This construction method composes a ray of a spot without a camera. Therefore, this construction method doesn't need many cameras. Lastly, this paper considers a construction method of dense ray space using depth components.

Guided visibility sampling

This paper addresses the problem of computing the triangles visible from a region in space. The proposed aggressive visibility solution is based on stochastic ray shooting and can take any triangular model as input. We do not rely on connectivity information, volumetric occluders, or the availability of large occluders, and can therefore process any given input scene. The proposed algorithm is practically memoryless, thereby alleviating the large memory consumption problems prevalent in several previous algorithms. The strategy of our algorithm is to use ray mutations in ray space to cast rays that are likely to sample new triangles. Our algorithm improves the sampling efficiency of previous work by over two orders of magnitude.

RAYSET: A TAXONOMY FOR IMAGE-BASED RENDERING

A new concept, referred to as rayset, is discussed in this paper. It is a parametric function consisting of two mapping relations. The first one maps from a parameter space to the ray space, while the second one maps from the parameter space to the attribute space. A taxonomy is proposed based on the rayset concept whereby scene representations and scene reconstruction techniques used in image-based rendering are individually classified. Existing image-based rendering techniques are surveyed under the proposed classification. The review shows that different image-based scene representations, such as multiple-center-of-projection image and concentric mosaics, can be cast as different kinds of raysets. Different scene reconstruction approaches can be regarded as attempts to render different raysets. The concepts of rayset warping and rayset editing are also formulated. Under the rayset taxonomy, both techniques try to alter one of the mapping relations defined by a rayset without changing the other one.