Cosmic Electrons Research Articles

Assimilation of FORMOSAT‐3/COSMIC electron density profiles into a coupled thermosphere/ionosphere model using ensemble Kalman filtering

This paper presents our effort to assimilate FORMOSAT‐3/COSMIC (F3/C) GPS Occultation Experiment (GOX) observations into the National Center for Atmospheric Research (NCAR) Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE‐GCM) by means of ensemble Kalman filtering (EnKF). The F3/C electron density profiles (EDPs) uniformly distributed around the globe which provide an excellent opportunity to monitor the ionospheric electron density structure. The NCAR TIE‐GCM simulates the Earth's thermosphere and ionosphere by using self‐consistent solutions for the coupled nonlinear equations of hydrodynamics, neutral and ion chemistry, and electrodynamics. The F3/C EDP are combined with the TIE‐GCM simulations by EnKF algorithms implemented in the NCAR Data Assimilation Research Testbed (DART) open‐source community facility to compute the expected value of electron density, which is ‘the best’ estimate of the current ionospheric state. Assimilation analyses obtained with real F3/C electron density profiles are compared with independent ground‐based observations as well as the F3/C profiles themselves. The comparison shows the improvement of the primary ionospheric parameters, such as NmF2 and hmF2. Nevertheless, some unrealistic signatures appearing in the results and high rejection rates of observations due to the applied outlier threshold and quality control are found in the assimilation experiments. This paper further discusses the limitations of the model and the impact of ensemble member creation approaches on the assimilation results, and proposes possible methods to avoid these problems for future work.

Modeling and observations of the low latitude ionosphere‐plasmasphere system at long deep solar minimum

The behavior of the low latitude ionosphere‐plasmasphere system in American‐Brazilian longitudes (30°W–120°W) in three seasons at the long deep solar minimum (2006–2010) is investigated using the theoretical model SUPIM and FORMOSAT‐3/COSMIC electron density and GIM‐TEC data. The data and model reveal some new aspects primarily for the low solar EUV fluxes. The ionosphere develops as a thin layer in the morning though becomes nearly as strong as that at normal solar minimum at around diurnal maximum (14 LT). However, after sunset the ionosphere‐plasmasphere system decays rapidly to become an extremely weak cold system prior to sunrise (05 LT) when the ionosphere contracts to about 1/3rd as strong as that at normal solar minimum, with peak density only about 1.8 × 105 cm−3, half width only about 150 km, and O+/H+ transition height as low as 475 km where the ion densities are only 104 cm−3 and ion temperatures are only 600 K. The mechanical effects of the neutral wind dominate over other processes, which causes the disappearance of the well known winter anomaly in TEC and Nmax, and lowest O+/H+ transition height (∼650 km at 14 LT and 475 km at 05 LT) occurring at around ±15° magnetic latitudes where the mechanical effects optimize. In addition, the ionosphere becomes weakest about 7 months after the solar activity dipped to the lowest level in 2008.

Multi messenger astronomy and CTA: TeV cosmic rays and electrons

Cosmic rays are a sample of solar, galactic and extragalactic matter. Their origin and properties are one of the most intriguing question in modern astrophysics. The most energetic events and active objects in the Universe: supernovae explosion, pulsars, relativistic jets, active galactic nuclei, have been proposed as sources of cosmic rays although unambiguous evidences have still to be found. Electrons, while comprising ∼1% of the cosmic radiation, have unique features providing important information regarding the origin and propagation of cosmic rays in the Galaxy that is not accessible from the study of the cosmic-ray nuclear components due to their differing energy-loss processes. In this paper we will analyse, discussing the experimental uncertainties and challenges, the most recent measurements on cosmic-ray nuclei and, in particular, electrons with energies from tens of GeV into the TeV region.

Global response of the ionosphere to atmospheric tides forced from below: Comparison between COSMIC measurements and simulations by atmosphere‐ionosphere coupled model GAIA

This paper for the first time presents a detailed comparison between simulated and observed global electron density responses to different atmospheric tides forced from below. The recently developed Earth's whole atmospheric model from the troposphere to the ionosphere, called GAIA, has been used for the simulation of the electron density tidal responses. They have been compared with the extracted from the COSMIC electron density data tidal responses for the period of time October 2007 to March 2009. Particular attention has been paid to the nonmigrating DE3/DE2 and migrating DW1, SW2 and TW3 electron density responses. The GAIA model reproduced quite well the COSMIC DE3/DE2 responses. Both simulations and observations revealed three altitude regions of enhanced electron density responses: (1) an upper level response, above 300 km height, apparently shaped mainly by the “fountain effect”; (2) a response located near altitudes of ∼200–270 km, and (3) a lower thermospheric response situated near 120–150 km height. A possible mechanism is suggested for explaining the two lower level responses. For the first time the GAIA model simulations supported the observational evidence found in the COSMIC measurements that the ionospheric WN4 (WN3) longitude structure is not generated only by the DE3 (DE2) tide as it has been often assumed. As regards the comparison of the migrating DW1, SW2 and TW3 responses the obtained results clearly demonstrate that the GAIA model reproduce very well of the SW2 and TW3 COSMIC electron density responses. The only main discrepancy is seen in the migrating DW1 response; the observation does not support the splitting of the simulated response at both sides of the equator. This is due mainly to the difference between the SABER and GAIA SW2 tide in the lower thermosphere as it turned out that the DW1 electron density response strongly depends on the mean features of the lower thermospheric SW2 tide.

Earth magnetic field effects on the cosmic electron flux as background for Cherenkov Telescopes at low energies

Cosmic ray electrons and positrons constitute an important component of the background for imaging atmospheric Cherenkov Telescope Systems with very low energy thresholds. As the primary energy of electrons and positrons decreases, their contribution to the background trigger rate dominates over protons, at least in terms of differential rates against actual energies. After event reconstruction, this contribution might become comparable to the proton background at energies of the order of few GeV. It is well known that the flux of low energy charged particles is suppressed by the Earth’s magnetic field. This effect strongly depends on the geographical location, the direction of incidence of the charged particle and its mass. Therefore, the geomagnetic field can contribute to diminish the rate of the electrons and positrons detected by a given array of Cherenkov Telescopes.In this work we study the propagation of low energy primary electrons in the Earth’s magnetic field by using the backtracking technique. We use a more realistic geomagnetic field model than the one used in previous calculations. We consider some sites relevant for new generations of imaging atmospheric Cherenkov Telescopes. We also study in detail the case of 5@5, a proposed low energy Cherenkov Telescope array.

Sudden intensity increases and radial gradient changes of cosmic ray MeV electrons and protons observed at Voyager 1 beyond 111 AU in the heliosheath

Voyager 1 has entered regions of different propagation conditions for energetic cosmic rays in the outer heliosheath at a distance of about 111 AU from the Sun. The low energy 6–14 MeV galactic electron intensity increased by ~20% over a time period ≤10 days and the electron radial intensity gradient abruptly decreased from ∼19%/AU to ∼8%/AU at 2009.7 at a radial distance of 111.2 AU. At about 2011.2 at a distance of 116.6 AU a second abrupt intensity increase of ∼25% was observed for electrons. After the second sudden electron increase the radial intensity gradient increased to 18%/AU. This large positive gradient and the ∼13 day periodic variations of >200 MeV particles observed near the end of 2011 indicate that V1 is still within the overall heliospheric modulating region. The implications of these results regarding the proximity of the heliopause are discussed.

Thermosphere–ionosphere coupling in response to recurrent geomagnetic activity

The paper presents the global thermosphere–ionosphere response to the high-speed solar wind streams and the subsequent recurrent geomagnetic variations with a period of 9d during the period of time 1 October 2007–31 March 2009. The COSMIC electron density at fixed heights, as well as the ionospheric parameters foF2 and hmF2, and the two coefficients characterizing the top and bottom side vertical gradients of the electron density profile, are used for investigating the ionospheric 9-d (s=0) wave response. The SABER temperature data are utilized for studying the response of the lower thermosphere to the recurrent auroral heating. The COSMIC and SABER measurements are analyzed by one and the same method where the atmospheric tides and planetary waves which are present in the temperature and electron density measurements are simultaneously extracted from the data. The use of such data analysis approach brings to light additional features of the ionospheric response to a recurrent geomagnetic activity which have not been found before.

Cosmic ray Monte Carlo: A global fitting method in studying the properties of the new sources of cosmice±excesses

Recently PAMELA collaboration published the cosmic nuclei and electron spectra with high precision, together with the cosmic antiproton data updated, and the Fermi-LAT collaboration also updated the measurement of the total $e^+e^-$ spectrum to lower energies. In this paper we develop a Markov Chain Monte Carlo (MCMC) package {\it CosRayMC}, based on the GALPROP cosmic ray propagation model to study the implications of these new data. It is found that if only the background electrons and secondary positrons are considered, the fit is very bad with $\chi_{\rm red}^2 \approx 3.68$. Taking into account the extra $e^+e^-$ sources of pulsars or dark matter annihilation we can give much better fit to these data, with the minimum $\chi_{\rm red}^2 \approx 0.83$. This means the extra sources are necessary with a very high significance in order to fit the data. However, the data show little difference between pulsar and dark matter scenarios. Both the background and extra source parameters are well constrained with this MCMC method. Including the antiproton data, we further constrain the branching ratio of dark matter annihilation into quarks $B_q<0.5%$ at $2\sigma$ confidence level. The possible systematical uncertainties of the present study are discussed.

Improvement of retrieved FORMOSAT-3/COSMIC electron densities validated by ionospheric sounder measurements at Jicamarca

[1] Inversion techniques applied to GPS-LEO radio occultation data allow the retrieval of accurate and worldwide-distributed refractivity profiles, which, in the case of the ionosphere, can be converted into electron densities providing information regarding the electron content distribution in this atmospheric region. In order to guarantee the accuracy of the electron density retrievals, two key points should be taken into account: the horizontal gradients of the electronic distribution and the topside electron content above the LEO orbit. The deployment in April 2006 of the satellite Constellation Observing System for Meteorology Ionosphere and Climate (FORMOSAT-3/COSMIC), carrying GPS receivers on board, provides valuable radio occultation data with global and almost uniform coverage overcoming the sparsity of data from previous LEO missions (for instance, GPS/MET, CHAMP, and SAC-C). This is also one of the main limitations of other sources providing direct observations, such as ionosondes. In this study, the improved Abel transform inversion is used to analyze derived ionospheric electron density profiles of the whole year 2007 in a scenario with very high electron density gradients: The neighboring area of Jicamarca (76.9°W, 12°S, dip latitude: 1°N), Peru, located at very low latitude and close to the geomagnetic equator, and the influence of the Appleton-Hartree equatorial anomaly (Davies, 1990). Moreover, different strategies to account for the topside electron content in the occultation data inversion are compared and discussed, taking advantage of the availability of FORMOSAT-3/COSMIC data sets and manually calibrated measurements from Jicamarca DPS. Statistical results show that for the current scenario the improvements are only about 10%, evidencing that the lack of colocation is one important source of error for the classical Abel inversion. Implications with respect to the plasmaspheric contribution have been derived from this data set analysis, in particular, the necessity to account for it specially when the Total Electron Content (TEC) is small.

Antiproton modulation in the Heliosphere and AMS-02 antiproton over proton ratio prediction

We implemented a quasi time-dependent 2D stochastic model of solar modulation describing the transport of cosmic rays (CR) in the heliosphere. Our code can modulate the Local Interstellar Spectrum (LIS) of a generic charged particle (light cosmic ions and electrons), calculating the spectrum at 1AU. Several measurements of CR antiparticles have been performed. Here we focused our attention on the CR antiproton component and the antiproton over proton ratio. We show that our model, using the same heliospheric parameters for both particles, fit the observed anti-p/p ratio. We show a good agreement with BESS-97 and PAMELA data and make a prediction for the AMS-02 experiment.

Searching for TeV cosmic electrons with the CREST experiment

The Cosmic Ray Electron Synchrotron Telescope (CREST) high-altitude balloon experiment is a pathfinding effort to detect for the first time multi-TeV cosmic-ray electrons. Such would be the markers of nearby cosmic accelerators, as energetic electrons from distant Galactic sources are expected to be depleted by radiative losses during interstellar transport. Electrons will be detected indirectly by the characteristic signature of their geomagnetic synchrotron losses, in the form of a burst of coaligned x-ray photons intersecting the plane of the instrument. Since the primary electron itself need not traverse the payload, an effective detection area is achieved that is several times the nominal 6.4 m 2 instrument. The payload is composed of an array of 1024 BaF2 crystals surrounded by a set of veto scintillator detectors. A long-duration balloon flight in Antarctica is planned for the 2011-12 season.

Global ionospheric response to nonmigrating DE3 and DE2 tides forced from below

[1] In this paper we present the global spatial structure and seasonal variability of the COSMIC electron density response to the forced from below DE3 and DE2 tides during the period January 2008 to March 2009. The COSMIC electron density at fixed altitudes and SABER temperatures were utilized in order to define the ionospheric DE3 and DE2 tidal response to the DE3 and DE2 temperature tides coming from below. The tidal waves from both data sets have been extracted by the same data analysis method. The latitude structure of the ionospheric response for heights up to 450–500 km is distributed on both sides of the dip equator at about ±30° modified dip latitude; above 500 km the response is approximately confined over the equator. Two altitude regions of enhanced ionospheric response are found: an upper level response (above 300 km) and a bottom level one (below 250 km); the two regions are separated by a narrow altitude zone with no tidal response. The different phase structure of the ionospheric response in both altitude regions suggests that (1) the upper level response is mainly due to the DE3/DE2 modulated vertical plasma drift and (2) the bottom level response is complex and, in all likelihood, is caused by more than one mechanism.

Stratospheric warmings: The atmosphere–ionosphere coupling paradigm

The paper presents for the first time the global spatial (latitude and altitude) structure of the mean ionospheric response to sudden stratospheric warming (SSW) events in winters of 2007/2008 and 2008/2009. To elucidate the effect of the SSWs on the ionosphere the COSMIC f oF2, h mF2, and electron density data at fixed altitudes are analyzed. Both the mean f oF2 and h mF2 parameters and the mean electron density at fixed heights indicate regular negative responses to the SSW temperature pulses at high latitudes. Similar response is found for the diurnal variability of the COSMIC electron density. The response is confined mainly to low and middle latitudes. A possible mechanism causing the observed negative ionospheric response is suggested.

Magnetic field contribution to the last electron–photon scattering

When the cosmic microwave photons scatter electrons just prior to the decoupling of matter and radiation, magnetic fields do contribute to the Stokes matrix as well as to the scalar, vector and tensor components of the transport equations for the brightness perturbations. The magnetized electron–photon scattering is hereby discussed in general terms by including, for the first time, the contribution of magnetic fields with arbitrary direction and in the presence of the scalar, vector and tensor modes of the geometry. The propagation of relic vectors and relic gravitons is discussed for a varying magnetic field orientation and for different photon directions. The source terms of the transport equations in the presence of the relativistic fluctuations of the geometry are also explicitly averaged over the magnetic field orientations and the problem of a consistent account of the small-scale and large-scale magnetic field is briefly outlined.

Leptonic dark matter annihilation in the evolving universe:constraints and implications

The cosmic electron and positron excesses have been explained aspossible dark matter (DM) annihilation products. In this work weinvestigate the possible effects of such a DM annihilation scenarioduring the evolution history of the Universe. We first calculate theextragalactic γ-ray background (EGRB), which is producedthrough the final state radiation of DM annihilation to chargedleptons and the inverse Compton scattering betweenelectrons/positrons and the cosmic microwave background. The DM haloprofile and the minimal halo mass, which are not yet well determinedfrom the current N-body simulations, are constrained by the EGRBdata from EGRET and Fermi telescopes. Then we discuss the impact ofsuch leptonic DM models on cosmic evolution, such as thereionization and heating of intergalactic medium, neutral Hydrogen21 cm signal and suppression of structure formation. We show thatthe impact on the Hydrogen 21 cm signal might show interestingsignatures of DM annihilation, but the influence on star formation isnot remarkable. Future observations of the 21 cm signals could beused to place new constraints on the properties of DM.

Spectral measurements of imaging plate backgrounds, alpha-particles and beta-particles

Background radiation and radioactive sources have been measured with laser-scanned phosphor imaging plates using an image processing method that produces spectra. This enables distinction between ambient background radiation, alpha and beta radionuclides and provides a means for quantitation. The background counts span a broad spectral continuum, whereas counts resulting from alpha and beta activity are restricted to certain regions within the background continuum spectrum. The alpha-counting spectral region has a background count rate of <0.01 counts mm −2 h −1. The beta-counting region has a count rate of <1 count mm −2 h −1. One region of the background spectrum is attributed to heavy ions from cosmic rays and has a count rate of <1 count cm −2 day −1. With regard to imaging spectrometry, beta-particles from 3H ( E max=0.0186 MeV) could be distinguished from higher energy beta-particles such as those from 14C ( E max=0.157 MeV) and 40K ( E max=1.33 MeV). Beta-particles can be distinguished from alpha-particles, and radionuclide counts can be distinguished from the background. The spectral characterization of the background, alpha-particles and beta-particles is expected to support applications in cosmic ray, heavy ion, radionuclide and electron studies.

Investigation of Radiation Hardness of Germanium Photovoltaic Cells

This contribution discusses the radiation hardness of germanium (Ge) photovoltaic cells under space conditions corresponding to an irradiation dose of 1-MeV 1 × 1015 cm-2 electrons. For this purpose, different germanium photovoltaic cell technologies based on p-type substrates are analyzed. The investigation comprises standard Ge photovoltaic cells with a substrate doping concentration of NA = 1 × 1017 cm-3, as well as recently developed Ge photovoltaic devices with extended quantum efficiency in the IR (λ > nm), which are based on low-doped substrates with NA = 1-4 × 1016 cm-3 in conjunction with an electrical rear-side passivation layer. In comparison to the standard Ge photovoltaic cell design, higher germanium subcell current densities of up to 14% at begin of life and up to 13% after electron exposure are achieved. This is particularly advantageous for high-efficiency metamorphic GaInP/GaInAs/Ge triple-junction solar cell structures, where the Ge subcell may become current limiting. Measurement results are presented, showing that the quantum efficiency related to the direct and indirect absorption transitions is differently affected by the cosmic electron particle irradiation. Furthermore, the impact of irradiation on free carrier absorption processes is discussed.

Future balloon experiments for electron and positron measurements at high energy

A large interest has been triggered by the recent direct measurements of cosmic positrons and electrons. They include: the anomalous positron abundance reported by PAMELA; the spectral “feature” suggested by the analysis of the inclusive electron and positron data of the ATIC balloon experiment; the results of FERMI and H.E.S.S. experiments. Further accurate measurements, with smaller systematic errors, might clarify the present experimental scenario. While measurements of dipole asymmetries and of the electron spectrum above 1 TeV may require a space mission to provide a sufficient exposure, balloons can investigate the spectral shape below 1 TeV and contribute to the clarification of the, so-called, “ATIC anomaly”. A concise review will be presented of the main balloon missions that have been specifically designed to provide new electron measurements in the near future.

CAN DARK MATTER ANNIHILATION ACCOUNT FOR THE COSMIC e± EXCESSES?

In the talk I give a brief review of the works related with the recent results from PAMELA, ATIC and Fermi about the cosmic electron and positron excesses. Especially I introduce constraints gotten from astrophysical observations on the DM annihilation scenario to account for the cosmic electron excess.

A prototype of fine granularity lead-scintillating fiber calorimeter with imaging read out

The construction and tests performed on a smal prototype of lead-scintillating fiber calorimeter instrumented with multianode photomultipliers are reported. The prototype is 15 cm wide, 15 radiation lenghts deep and is made of 200 layers of 50 cm long fibers. One side of the calorimeter has been instrumented with an array of 3 × 5 multianode R8900-M16 Hamamatsu photomultipliers, each segmented with a matrix of 4 × 4 anodes. The read-out granularity is 240 pixels 11 × 11 mm 2 reading about 64 fibers each. They are interfaced to the 6 × 6 mm 2 pixelled photocade with truncated pyramid light guides made of BC-800 plastic, UV transparent. Moreover each photomultiplier provides also the OR information of the last 12 dynodes. This information can be useful for trigger purposes. The response of the individual anodes, their relative gain and cross-talk has been measured with a 404 nm picosecond laser illuminating only a few fibers on the opposite side of the read-out. We also present first results of the calorimeter response to cosmic rays and electron beam data collected at BTF facility in Frascati.