Observation of Thunderstorm Ground Enhancements with intense fluxes of high-energy electrons

The high altitude (∼3200 m above sea level) of Aragats Space Environmental Center (ASEC) and low elevation of the thunderclouds provides a good opportunity to detect Thunderstorm Ground Enhancements (TGEs), particles of which rapidly attenuate in the atmosphere. In 2012, we have estimated the energy spectra of several TGEs and revealed significant electron fluxes extended till 30–40 MeV. Measured in the one and the same event gamma ray and electron fluxes allow to estimate the height of the thundercloud above the detector. Proceeding from the energy spectra and the height of the cloud we estimate the electron spectra on the exit from the electric field of the thundercloud, the number of excess electrons in the cloud and avalanche multiplication rate.     

The maximum energy and spectra of cosmic rays accelerated in active galactic nuclei

Astronomy Letters - We computed the energy spectra of the incident (on an air shower array) ultrahigh-energy (E&;gt;4×1019eV) cosmic rays (CRs) that were accelerated in nearby Seyfert...     

Relative abundances of cosmic ray nuclei from neon to iron over Fort Churchill

The relative abundances of the nuclei from neon to iron in the energy interval 150–400 MeV/n have been estimated by using a balloon borne cellulose-nitrate plastic detector. The source abundances are obtained by extrapolating the near-earth abundances using leaky box model of cosmic ray propagation in the interstellar space. The results are compared with those of other investigators and a general agreement is obtained. However, a discrepancy arises especially in the case of Al which is not detected in the present investigation.     

North-south asymmetry of the heliosphere from cosmic-ray observations

The evidence that the heliosphere retains a pronounced north-south asymmetry during a long period (five solar cycles) is discussed. A modification of the standard model for the interplanetary magnetic field that provides the observed asymmetry is considered.     

暗物质空间探测器BGO量能器的读出设计

暗物质空间探测器是中国科学院紫金山天文台暗物质空间天文实验室提出的,其目的是为了探测暗物质粒子湮灭可能产生的高能电子和伽玛粒子.整个探测器主要由BGO(Bismuth germanate,锗酸铋)高能图像量能器和闪烁体径迹探测器构成.探测器的能量探测范围将覆盖10 GeV到10 TeV的高能电子和伽玛粒子,其中高能粒子的能量主要沉积在BGO量能器中.为了验证探测器方案,紫金山天文台暗物质空间天文实验室设计了暗物质空间探测器BGO量能器的读出系统原型,并对其进行了初步的测试.     

Small-scale anisotropy of cosmic rays with energies above 3×1018 eV based on data from the Yakutsk EAS facility

We analyze the directions of the arrival of cosmic rays with energies E ₀≥3×10¹⁸ eV and zenith angles θ≤45° recorded by the Yakutsk extensive air shower (EAS) facility during 1974–2000. They are shown to have a small-scale structure with scale sizes of 5°–10°. Enhanced particle fluxes compared to the expected levels for random distributions at (4–5)σ are observed from the Galactic and Supergalactic planes.     

Quasi-linear perpendicular diffusion coefficients of charged cosmic rays calculated directly from the Newton–Lorentz equation

It is the subject of this article to determine diffusion coefficients of charged test particles perpendicular to a mean magnetic field analytically by starting directly from the Newton–Lorentz equation. We employ the so-called standard quasi-linear theory to test the well-known field line random walk limit. It is demonstrated in this article that there is an additional gyroresonant contribution which describes the scattering of the particle away from a single field line. For certain situations, this additional contribution is small and can be neglected. For other cases, we obtain new results such as a rigidity-dependent quasi-linear perpendicular mean free path. The results of this article are relevant for particles in the solar wind which move scatter free or nearly scatter free in the direction parallel to the magnetic field of the Sun.     

Efficiency of cosmic ray reflections from an ultrarelativistic shock wave

The process of cosmic ray acceleration up to energies in excess of 10²⁰ eV at relativistic shock waves with large Lorentz factors, Γ≫1, requires ∼Γ² particle energy gains at single reflections from the shock (cf. Gallant & Achterberg). In the present Letter , by applying numerical simulations we address an efficiency problem arising for such models. The actual efficiency of the acceleration process is expected to be substantially lower than the estimates of previous authors.     

Design of the Prototype Readout System of BGO Calorimeter in the Space Dark Matter Detector of Purple Mountain Observatory

A space dark matter detector is proposed by the Key Laboratory of Dark Matter And Space Astronomy of Chinese Academy of Sciences for detecting the high-energy electrons and Gamma particles produced by the annihilation of dark matter in space. The whole detector is mainly composed of the BGO (bismuth germanium oxide) high-energy image calorimeter and scintillation hodoscope. The energy range of the detector will cover the high-energy electrons and Gamma particles of 10 Gev∼10 TeV, in which the energies of high-energy particles are mainly deposited in the BGO calorimeter. For verifying the scheme of the detector, we have designed a prototype readout system for the BGO calorimeter of the space dark matter detector, and made a preliminary test on it.     

Thermal instability and the effects of cosmic-ray diffusion

We study the dynamical effects of cosmic rays (CRs) on thermal instability in the linear regime. CRs and the thermal plasma are treated as two different interacting fluids, in which CRs can diffuse along the magnetic field lines. We show that the growth rate of the magnetothermal condensation mode is reduced because of the existence of CRs, and this stabilizing effect depends on the diffusion coefficient and the ratio of CR pressure to gas pressure. Thus, a slower rate of structure formation via thermal instability is predicted when CRs are considered.     

Radio pulses from ultra-high energy atmospheric showers as the superposition of Askaryan and geomagnetic mechanisms

Radio emission in atmospheric showers is currently interpreted in terms of radiation due to the deviation of the charged particles in the magnetic field of the Earth and to the charge excess (Askaryan effect). Each of these mechanisms has a distinctive polarization. The complex signal patterns can be qualitatively explained as the interference (superposition) of the fields induced by each mechanism. In this work we explicitly and quantitatively test a simple phenomenological model based on this idea. The model is constructed by isolating each of the two components at the simulation level and by making use of approximate symmetries for each of the contributions separately. The results of the model are then checked against full ZHAireS Monte Carlo simulations of the electric field calculated from first principles. We show that the simple model describes radio emission at a few percent level in a wide range of shower-observer geometries and on a shower-by-shower basis. As a consequence, this approach provides a simple method to reduce the computing time needed to accurately predict the electric field of radio pulses emitted from air showers, with many practical applications in experimental situations of interest.     

The dynamical coupling of cosmic rays and magnetic field in galactic disks

In this paper we demonstrate the importance of cosmic rays for the dynamics of the interstellar medium. We present the first 3D-MHD numerical simulations of the Parker instability triggered by cosmic rays accelerated in supernova remnants. We show that in the presence of galactic rotation a net radial magnetic field is produced as a result of the cosmic ray injection. This process provides a very efficient magnetic field amplification within the general frame of so called fast galactic dynamo proposed by Parker (1992). This revised version was published online in September 2006 with corrections to the Cover Date.     

The Converter Mechanism of Particle Acceleration and Its Applications to the Unidentified Egret Sources

We discuss the properties of gamma-ray radiation accompanying the acceleration of cosmic rays via the converter mechanism. The mechanism exploits multiple photon-induced conversions of high-energy particles from charged into neutral state (namely, protons to neutrons and electrons to photons) and back. Because a particle in the neutral state can freely cross the magnetic field lines, this allows to avoid both particle losses downstream and reduction in the energy gain factor, which normally takes place due to highly collimated distribution of accelerated particles. The converter mechanism efficiently operates in relativistic outflows under the conditions typical for Active Galactic Nuclei, Gamma-Ray Bursts, and microquasars, where it outperforms the standard diffusive shock acceleration. The accompanying radiation has a number of distinctive features, such as an increase of the maximum energy of synchrotron photons and peculiar radiation beam-pattern, whose opening angle is much wider at larger photon energies. This provides an opportunity to observe off-axis relativistic jets in GeV–TeV energy range. One of the implications is the possibility to explain high-latitude unidentified EGRET sources as off-axis but otherwise typical relativistic-jet sources, such as blazars.     

Limb Spicules from the Ground and from Space

We amassed statistics for quiet-sun chromosphere spicules at the limb using ground-based observations from the Swedish 1-m Solar Telescope on La Palma and simultaneously from NASA’s Transition Region and Coronal Explorer (TRACE) spacecraft. The observations were obtained in July 2006. With the 0.2 arcsecond resolution obtained after maximizing the ground-based resolution with the Multi-Object Multi-Frame Blind Deconvolution (MOMFBD) program, we obtained specific statistics for sizes and motions of over two dozen individual spicules, based on movies compiled at 50-second cadence for the series of five wavelengths observed in a very narrow band at Hα, on-band and at ± 0.035 nm and ± 0.070 nm (10 s at each wavelength) using the SOUP filter, and had simultaneous observations in the 160 nm EUV continuum from TRACE. The MOMFBD restoration also automatically aligned the images, facilitating the making of Dopplergrams at each off-band pair. We studied 40 Hα spicules, and 14 EUV spicules that overlapped Hα spicules; we found that their dynamical and morphological properties fit into the framework of several previous studies. From a preliminary comparison with spicule theories, our observations are consistent with a reconnection mechanism for spicule generation, and with UV spicules being a sheath region surrounding the Hα spicules.     

The observation of extensive air showers from an Earth-orbiting satellite

We review the main issues that are relevant for the observation of extensive air showers from an Earth-orbiting satellite. Extensive air showers are produced by the interaction of ultra-high energy cosmic particles with the atmosphere and can be observed by an orbiting telescope detecting the air scintillation light.We provide the main analytical formulas and semi-analytical results needed to optimize the design of a suitable telescope and estimate the best-expected performance and the minimal necessary requirements for the observation.While we have in mind an EUSO-like general-purpose experiment, the results presented in this paper are useful for any kind of space-based experiment.     

Probable spectral steepening of UHEγ-rays of nuclear origin and its consequences

Recent accelerator data based parameterization of the inclusive cross section (c −s) forπ0 production in hadronic collisions and an explicit incorporation of the finiteness of the relevant projectile hadron spectrum suggest a significant steepening in the spectrum (by as much as 0.4 in the spectral index) of the secondaryγ-ray towards the end of the spectrum. We emphasize here that this spectral steepening in conjunction with the possibility that in the bright X-ray binaries the maximum energy to which theγ-ray producing progenitor protons may be accelerated is only ∼ l0 PeV, may imply an effective efficiency forγ-ray production,ε, as reckoned by the PeV arrays, one or two orders smaller than the previous estimates. To explain the genesis of a given PeV photon flux from an X-ray binary, one, therefore, has to. accordingly consider a much higher value of the progenitor proton beam luminosity,L _p . This requirement may raise further questions regarding the actual genesis of PeVγ-rays in X-ray binaries, or alternatively, on the veracity of the high values of the PeV photon fluxes reported by earlier experiments.     

Drift Scanning from Ground and in Space

The drift scanning technique offers, in principle, a simple and efficientmethod for imaging wide regions of the sky with intrinsic high astrometricaccuracy. Its performance is analyzed in two distinct environments, namelyfrom a small class ground based telescope and a spaceborne interferometer. Inparticular, the study is referred to the proposed ESA cornerstone missionGAIA (Global Astrometric Interferometer for Astrophysics).The constant clock rate of a CCD, due to the declination dependentsidereal speed variation, results in a systematic image smearing, whichlimits the positional accuracy. Moreover, the readout timing accuracyprovides an additional random noise corresponding to a drift speed jitter.Stability requirements on the order of 10-6 or better have to be fulfilledfor the space option.Both effects can be addressed by proper system design; provisionalimplementation strategies are discussed for both applications.