Cosmic Electrons Research Articles

A study of the Weddell Sea Anomaly observed by FORMOSAT‐3/COSMIC

More than two years of COSMIC electron density profiles at low solar activities are collected to study the evolution of the Weddell Sea Anomaly (WSA), which appears as an evening enhancement in electron density during local summer. Observations show that the change in NmF2 (the F2 peak electron density) is associated with the change in hmF2 (the F2 peak height), while the latter is correlated closely with the components of the geomagnetic field. We find that (1) in the afternoon, hmF2 is more liable to rise drastically in regions with a larger ∣sin(2I)∣ value, which would occur early at certain declinations, eastward in the southern hemisphere and westward in the northern hemisphere; (2) subsequently, a larger increment of hmF2 is coincidentally followed by a stronger enhancement of NmF2 and the enhancement ends just around the local sunset; and (3) in midlatitudes, the evolution pattern of hmF2 in the evening of equinoxes and winter is similar to that in summer, albeit without a lasting NmF2 enhancement as that in summer. These features suggest that the NmF2 enhancement and the hmF2 increase could arise from the thermospheric wind effect, and solar photoionization plays a crucial role in the enhancement as well. The general midlatitude F2 layer enhancement in local summer evening is consistent with the WSA on the above features, indicating that the WSA is a manifestation, with a particular geometry of the magnetic field, of the evening enhancement induced by the winds.

A global survey of COSMIC ionospheric peak electron density and its height: A comparison with ground-based ionosonde measurements

With a network of ground-based ionosondes distributed around the world, the ionospheric peak electron density and its height measured by FORMOSAT-3/COSMIC satellites in terms of GPS radio occultation technique are extensively examined in this article. It is found that, in spite of the latitude, the mean values of the peak electron density measured by COSMIC satellites are systematically smaller than those observed by ground-based ionosondes. The discrepancy between them is dependent on the latitude, namely, it is small in low and mid-latitudes and large in high-latitude region. Moreover, statistical analysis shows that the slopes of the regression line that is best fitted to the scatter diagram of occultation-retrieved peak electron density (ordinate axis) versus ionosonde-observed peak density (abscissa axis) are universally less than one. This feature is believed to be the result of path average effect of non-uniform distribution of the electron density along the GSP ray during the occultation. A comparison between COSMIC-measured peak height and ionosonde-derived peak height hmF2 indicates that the former is systematically higher than the latter. The difference in the two can be as large as 20% or more in equatorial and low-latitude regions. This result implies that the peak height hmF2 derived from the virtual height through true height analysis based on Titheridge method seems to underestimate the true peak height. The correlation between COSMIC and ionosonde peak electron densities is analyzed and the result reveals that correlation coefficient seems to be dependent on the fluctuation of the occultation-retrieved electron density profile. The correlation will be higher (lower) for the electron density profiles with smaller (larger) fluctuations. This feature suggests that the inhomogeneous distribution of the electron density along the GPS ray path during the occultation plays an important role affecting the correlation between COSMIC and ionosonde measurements.

Visible and dark matter genesis and cosmic positron and electron excesses

Dark and baryonic matter contribute comparable energy density to the present universe. The dark matter may also be responsible for the cosmic positron and electron excesses. We connect these phenomena with the Dirac seesaw for neutrino masses. In our model (i) the dark matter relic density is a dark matter asymmetry generated simultaneously with the baryon asymmetry so that we can naturally understand the coincidence between the dark and baryonic matter and (ii) the dark matter mostly decays into the leptons so that its decay can interpret the anomalous cosmic rays with positron and electron excesses.

Constraints on leptonically annihilating dark matter from reionization and extragalactic gamma background

The PAMELA, Fermi and HESS experiments (PFH) have shown anomalous excesses in the cosmic positron and electron fluxes. A very exciting possibility is that those excesses are due to annihilating dark matter (DM). In this paper we calculate constraints on leptonically annihilating DM using observational data on diffuse extragalactic gamma-ray background and measurements of the optical depth to the last-scattering surface, and compare those with the PFH favored region in the m_{DM} - <\sigma_A v> plane. Having specified the detailed form of the energy input with PYTHIA Monte Carlo tools we solve the radiative transfer equation which allows us to determine the amount of energy being absorbed by the cosmic medium and also the amount left over for the diffuse gamma background. We find that the constraints from the optical depth measurements are able to rule out the PFH favored region fully for the \tau^{-}+\tau^{+} annihilation channel and almost fully for the \mu^{-}+\mu^{+} annihilation channel. It turns out that those constraints are quite robust with almost no dependence on low redshift clustering boost. The constraints from the gamma-ray background are sensitive to the assumed halo concentration model and, for the power law model, rule out the PFH favored region for all leptonic annihilation channels. We also find that it is possible to have models that fully ionize the Universe at low redshifts. However, those models produce too large free electron fractions at z > ~100 and are in conflict with the optical depth measurements. Also, the magnitude of the annihilation cross-section in those cases is larger than suggested by the PFH data.

Construction and Performance of a High Granularity Calorimeter

We describe the realization and performance of a prototype high granularity calorimeter built with lead and scintillating fibers. We describe the calorimeter construction and show cosmic ray and electron test beam results obtained with a custom-designed trigger.

Three‐dimensional ionospheric electron density structure of the Weddell Sea Anomaly

This paper provides the first three‐dimensional description of the ionospheric density structure of the Weddell Sea Anomaly (WSA). The WSA is characterized by a nighttime ionospheric density greater than that in daytime in the Weddell Sea region around the Antarctic Peninsula during the southern hemisphere summer. It was first observed by ground‐based ionosondes located in the Antarctica back in the 1950s and was further investigated by two‐dimensional maps over the oceans using TEC measurements collected by the TOPEX/Poseidon recently. Although these TEC maps have provided two‐dimensional views for tracking the time‐evolution and spatial coverage of the WSA, the vertical distribution of this peculiar feature is still unavailable. With the vertical ionospheric density profiles observed by the FORMOSAT‐3/COSMIC, three‐dimensional density structure of the WSA is presented here for the first time. Meanwhile, a similar WSA signature is observed in the northern and eastern hemisphere during June solstice by both the GPS‐TEC and the FORMOSAT‐3/COSMIC electron density observations. From the observed altitudinal structure of the WSA during 1800–2400 LT and the similar feature occurred in the opposite hemisphere suggest that the southward offset of the magnetic equator with respect to the geographic equator plays a major role for the WSA formation.

CALET Mission for the Observation of Cosmic Rays on the International Space Station

We have proposed CALET (CALorimetric Electron Telescope) mission to make observations of high energy cosmic rays, electrons, gamma-rays, and nuclei, on the International Space Station (ISS). CALET mission has been approved as one of candidates for the next mission utilizing the Japanese Experiment Module (JEM). The detector of CALET consists of an imaging calorimeter (IMC) and a total absorption calorimeter (TASC). Main objective of cosmic-ray observation with CALET is to determine precise energy spectrum of electrons up to 20 TeV. As the super nova remnants (SNR) are taken to be sources of electrons, some structure caused by nearby electron sources is expected to appear in the energy spectrum over 1 TeV. Gamma-rays from 20 MeV to a few TeV can be also observed by CALET. Because a thick TASC of CALET gives high energy resolution, annihilation line of SUSY particle, which is a candidate of the dark matter, can be detected. Observation of nuclei is also possible up to 1000 TeV owing to the thick TASC. We have been going on conceptual design of CALET to clear a next judgment in one or two years to proceed to practical development for launching in 2013.

Simulation Study on High Energy Cosmic Electron Detection by Shower Image

Many projects have recently been carried out and proposed for observing high energy electrons since it is realized that cosmic ray electrons are very important when studying the dark matter particles and the acceleration mechanism of cosmic rays. An imaging calorimeter, BETS (Balloon-borne Electron Telescope with Scintillator fiber), has been developed for this purpose. Using pattern analysis of the shower development, the electrons can be selected from those primary cosmic ray proton events with flux heights one-tenth that of the electrons. The Monte-Carlo simulation is indispensable for the instrument design, the signal trigger and the data analysis. We present different shower simulation codes and compare the simulation results with the beam test and the flight data of BETS. We conclude that the code FLUKA2002 gives the most consistent results with the experimental data.

Japanese polar patrol balloon experiments from 2002 to 2004

Polar patrol balloon experiments were carried out at Syowa Station in Antarctica from 2002 to 2004. Two balloons were launched for the purpose of observing phenomena in the polar atmosphere and one was done for the observation of high energy cosmic electrons. We developed a new housekeeping system including communication device using the Iridium satellite network, an auto-level controller driven by a new program for keeping the flight altitude, and a power management system for solar cells combined with secondary batteries. Two balloons for studying phenomena in the Antarctic atmosphere launched on January 13, 2003 made flights for 18 days and 25 days, respectively. All the housekeeping system worked well during the flights as we expected. Based on these experiments, we adjusted parameters for the altitude control system and the power management system. We launched a balloon for the cosmic electron observation on January 4, 2004. It flew 13 days around the Antarctica with the perfect operation of the onboard housekeeping system. We hope that fruitful scientific results will be obtained from these long-duration flights.

Observation of High Energy Cosmic Electrons by Long Duration Balloon in Antarctica(Current Topic)

Observation of High Energy Cosmic Electrons by Long Duration Balloon in Antarctica(Current Topic)

A hadronic tile calorimeter for the TESLA detector

Concept and design of a granular iron-scintillator sandwich calorimeter for the TESLA detector are shortly described and some recent R&D results for the light yield in the calorimeter tiles are discussed in view of further improvements. New types of sensitive semiconductor photodetectors with significant gain and insensitivity to the strong magnetic field are studied, some features and performance are discussed. A first prototype calorimeter assembled from ∼250 scintillator tiles is prepared for tests with cosmic muons and electrons (0.5–7 GeV) at DESY. These studies are needed to optimize construction and set up of a further 1 m 3 prototype with ∼4000 calorimeter cells for measurements in hadronic beams (1–50 GeV) in 2005/2006 and serve for test and improvement of the simulation tools for energy-flow measurements in jets and optimization of the mass reconstruction of multi-jet final states.

Scientific ballooning in Japan

Activities in scientific ballooning in Japan during 1998–1999 are reported. The total number of scientific balloons flown in Japan in 1998 and 1999 was sixteen, eight flights in each year. The scientific objectives were observations of high energy cosmic electrons, air samplings at various altitudes, monitoring of atmospheric ozone density, Galactic infrared observations, and test flights of new type balloons. Balloon expeditions were conducted in Antarctica by the National Institute of Polar Research, in Russia, in Canada and in India in collaboration with foreign countries' institutes to investigate cosmic rays, Galactic infrared radiation, and Earth's atmosphere. There were three flights in Antarctica, four flights in Russia, three flights in Canada and two flights in India. Four test balloons were flown for balloon technology, which included pumpkin-type super-pressure balloon and a balloon made with ultra-thin polyethylene film of 3.4 μm thickness.

Performance of TPC detector for the double β-decay experiment

A Large Time Projection Chamber (TPC) in a magnetic field designed to search for neutrinoless double β-decay of different isotopes is now operational. The TPC construction, high voltage drift supply, multiwire detectors, gas system is described. The first tracks from cosmic muons and background electrons have been obtained. Our goal is two neutrino double β-decay of 136Xe.

The cosmic electron background in low energy imaging atmospheric Cherenkov telescopes: effect of the geomagnetic field

A new generation of low threshold imaging atmospheric Cherenkov telescopes (IACTs) may reach γ-ray energies about 10 GeV with high sensitivities and very large collection areas. At these low energies cosmic electrons significantly contribute to the telescope background and are in principle indistinguishable from γ-rays. In this paper we estimate the electron background expected for two configurations of the low energy IACT MAGIC. We discuss in particular the reduction of the background caused by the geomagnetic field at different locations on the Earth's surface.

Preliminary study of a topological trigger device for cosmic-ray detectors

In view of implementing a topological trigger criterion in cosmic-ray detectors for efficient selection of required events a preliminary test has been done with a scintillating-fibre hodoscope using a position-sensitive photomultiplier. A space resolution of ∼0.6 mm in σ with a detection efficiency >97% has been obtained for charged particles of 5 GeV/c passing through 2×2 mm squared fibres. A custom-made discriminator, suppressing the cross-talk between adjacent fibres, allowed a better definition of track position even at high incident angles compared to the simple threshold discriminators. Simplicity as well as reliability of the prototype allow us to foresee a topological trigger device incorporated in different type of detectors, such as cosmic gamma or electron telescopes, solar neutron detectors and so on.

Possibility of increasing proton rejection by detecting primary cosmic radiation electrons using an ionization-neutron calorimeter

Measurements were made of the neutron yields from a lead absorber 60 cm thick in electromagnetic cascades initiated by 200–600 MeV electrons. A comparison between the neutron yields obtained for electrons and the results of similar measurements for protons and pions suggests that the rejection factor of the proton background is increased ∼102 times when an ionization-neutron calorimeter is used to measure primary cosmic radiation electrons at energies above 100 GeV.

Latitudinal distribution of &gt;106 MeV protons and its relation to the ambient solar wind in the inner southern and northern heliosphere: Ulysses Cosmic and Solar Particle Investigation Kiel Electron Telescope Results

We present observations and model calculations of the modulated intensities of galactic cosmic ray protons above 106 MeV/n along the Ulysses trajectory. Data are taken by the Cosmic and Solar Particle Investigation (COSPIN) Kiel Electron Telescope (KET) from spring 1993 to fall 1996. During this time period solar activity decreased and galactic cosmic rays recovered. To separate spatial from temporal variations we used the University of Chicago measurements from IMP 8 near Earth and compare the residual spatial variation with time independent modulation models. According to standard drift dominated modulation model, one would expect a radial gradient of ≈2%/AU and a latitudinal gradient of ≈1.2%/degree in both hemispheres. The measured mean radial gradient of «3%/AU is within the uncertainties in good agreement with the model predictions. However, the measured mean latitudinal gradient has a value of (0.33 ± 0.04)%/degree in both hemispheres at intermediate latitudes and is by a factor of 4 lower than expected. In the modified models the latitudinal gradient is in agreement with the measured ones when we increase the diffusion coefficient κθθ perpendicular to the magnetic field in polar direction to a value of 15% of the diffusion coefficient parallel to the magnetic field. The latitudinal gradients &gt;106 MeV protons calculated by modified modulation models are in very good agreement with the measured ones at intermediate latitudes. At lower latitudes, when Ulysses is embedded in the streamer belt, the models predict approximately the same latitudinal gradient than at intermediate latitudes, whereas the measured ones are significant smaller, or even vanishing. The observations support the previous conclusion from Paizis et al. [1995] that a significant latitudinal gradient is only observed when Ulysses is outside the streamer belt. Another remarkable observation is the difference of the radial gradient Gr at ∼3.5 AU in the southern (Gr≈3.5%/AU) and in the northern hemisphere (Gr≈2.3%/AU). Probable reasons for the significantly lower radial gradient in the northern hemisphere can be either a spatial asymmetry of the heliosphere or temporal variations.

Bremsstrahlung and Pair Creation by a Photon in the Spacetime of a Cosmic String

We consider two tree-graph processes in the spacetime of an infinite, straight and static cosmic string, namely Bremsstrahlung and electron–positron pair production. Results based on a simplified model with scalar fields which were obtained by other authors are extended to the more realistic QED case. In empty Minkowski spacetime, energy and momentum conservation preclude these processes. In spite of the local flatness of the metric, it is a topological defect that gives rise to non-conservation of momentum in the plane perpendicular to the string. Analytic expressions for the total transition probabilities and, in the case of Bremsstrahlung, the total radiation energy are found and compared with the results for the scalar field model. In a sense, the cylindrical mode solutions of the Dirac equation allow a spatial localisation of the decay processes relative to the string axis.

THE SEARCH FOR NEUTRINO SOURCES BEYOND THE SUN

It is hoped that in the near future, neutrino astronomy, born with the identification of thermonuclear fusion in the sun and the particle processes controlling the fate of a nearby supernova, will reach throughout and beyond our galaxy and make measurements relevant to cosmology, astrophysics, cosmic-ray physics and particle physics. The construction of a high-energy neutrino telescope requires a huge volume of very transparent, deeply buried material, such as ocean water or ice, which acts as the medium for detecting the particles. The AMANDA1 muon and neutrino telescope, now operating four strings of photomultiplier tubes buried in deep ice at the South Pole, is scheduled to be expanded to a ten-string array. The data collected over the first two years cover the three basic modes in which such instruments are operated: (i) the burst mode which monitors the sky for supernovae, (ii) the detection of electromagnetic showers initiated by PeV-energy cosmic electron neutrinos, and (iii) muon trajectory reconstruction for neutrino and gamma-ray astronomy. We speculate on the possible architectures of kilometer-scale instruments, using early data as a guideline.

Is the stable tau-neutrino really an allowable cold dark matter candidate?

Considering the annihilation of massive tau-neutrinos in the Galactic Halo, we show that it is difficult to obtain concordance between the observed (directly on indirectly) and predicted fluxes of cosmic electrons and positrons in the case of a stable tau-neutrino with mass m ≈ 1–24 MeV and magnetic moment μ ∼ 10 −6 μ B . These results exclude the possibility for such a tau-neutrino being the dominant cold dark matter particle component.