High temporal and spatial resolution observations of low energy electrons by a mother-daughter rocket in the vicinity of two quiescent auroral arcs

Low energy precipitated electrons have been measured with high time resolution through an auroral display by a series of high geometrical factor particle counters on a ‘mother-daughter’ sounding rocket, launched during wintertime near 2100 LT from Andenes, Norway.The observations show that the 0·5–3 keV electron fluxes are anisotropically distributed, with a maximum in a direction parallel to the local geomagnetic field vector at all latitudes covered by the rocket, except within the visual auroral forms where the pitch-angle distributions are isotropic or slightly peaked in a direction normal to the geomagnetic field. The 1 and 3 keV electron fluxes are weakly anticorrelated in the vicinity of the arcs, where also the 3 keV electron flux displays a more structured variation than the 0.5 and 1 keV electron fluxes.     

A high time resolution study of the solar wind-magnetosphere energy coupling function

A high time resolution study of the relationship between the solar wind-magnetosphere energy coupling function ? and the total energy dissipation rate U_T of the magnetosphere is made using 5-min average values of solar wind data and of the geomagnetic indices AE and Dst. All the results are essentially the same as those obtained by the earlier studies which were based on the hourly average data set. Therefore, we confirm that the magnetosphere is primarily a driven system.     

The swinging spring — Approximate analyses for low and very high energy,II

The two families of periodic solutions emanating from the lower equilibrium of a planar spring-pendulum system are analyzed both at and near resonance. Hamiltonian perturbation theory is used to obtain approximate formulas for the characteristic and the period of the motion. As the energy is increased to very high levels, a circulatory and an almost rectilinear periodic motion persist. Expressions for the trace of a stability matrix are determined for both these solutions. Comparisons are made throughout with accurate results from numerical integration.

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Résumé Les deux familles de solutions périodiques qui proviennent de l'équilibre inférieur d'un pendule élastique plan sont analysées pour le cas de résonnance et dans le voisinage de résonnance. On emploie la théorie perturbatrice Hamiltonienne pour obtenir des formules d'approximation pour la caractéristique et pour la période du mouvement. Quand l'énergie est augmentée à des niveaux très élevés, un mouvement périodique circulatoire et un mouvement périodique presque rectiligne sont préservés. Des expressions pour la trace d'une matrice de stabilité sont déterminées pour les deux familles de solutions périodiques. Des comparaisons sont faites entre les formules d'approximation et des résultats précis obtenus par l'integration numérique.

     

Electron temperatures in W51 complex from high resolution,low frequency radio observations

W51 is a giant radio complex lying along the tangent to the Sagitarius arm at a distance of about 7 kpc from the Sun, with an extension of about 1° in the sky. It is divided into three components A, B, C where W51A and W51B consist of many compact HII regions while W51C is a supernova remnant. We have made continuum radio observations of these HII regions of the W51 complex at 240, 610, 1060 and 1400 MHz using GMRT with lower resolution (20″ × 15″) at the lowest frequency. The observed spectra of the prominent thermal subcomponents of W51 have been fitted to a free-free emission spectrum and their physical properties like electron temperatures and emission measures have been estimated. The electron temperatures from continuum spectra are found to be lower than the temperatures reported from radio recombination line (RRL) studies of these HII regions indicating the need for a filling factor even at this resolution. Also, the observed brightness at 240 MHz is found to be higher than expected from the best fits suggesting the need for a multicomponent model for the region.     

A high resolution imaging detector for TeV gamma-ray astronomy

Details are presented of an atmospheric Cherenkov telescope for use in very high energy gamma-ray astronomy which consists of a cluster of 109 close-packed photomultiplier tubes at the focus of a 10 meter optical reflector. The images of the Cherenkov flashes generated both by gamma-ray and charged cosmic-ray events are digitized and recorded. Subsequent off-line analysis of the images improves the significance of the signal to noise ratio by a factor of 10 compared with non-imaging techniques.     

A search for very high energy bursts

Of great importance in distinguishing between models for gamma-ray bursts (GRBs) is the experimental determination of the highest energy gamma rays associated with bursts. The EGRET detection of a 15 GeV gamma ray indicates that the spectra of at least some bursts extend well beyond the several MeV limit of the BATSE detectors (Hurleyet al., 1994). The low expected flux means that the collecting area of the present generation of satellite-based detectors is too small to detect gamma rays much above this energy efficiently, and such searches are currently undertaken with ground based detectors. In this paper searches made for very high energy GRBs with a southern hemisphere air shower particle array are described.     

A rocket instrument for imaging the aurora by means of high speed photometric scanning

A high resolution rocket-borne mechanical flying spot scanner has evolved from similar ground-based instruments. The spinning motion of the rocket together with that of a motor-driven prism are used to scan a narrow-angle photometer systematically and repetitively over the full 4π sr region around the rocket. Outputs from two wavelengths selected by narrow-band interference filters are available from the one instrument. The large quantity of data thus obtained are first reproduced in pictorial form making it relatively easy to identify auroral and airglow features which can then be studied quantitatively. Computer reduction of the data also makes it possible to determine the attitude of the vehicle carrying the scanner to an accuracy better than can be achieved with an aspect magnetometer. Results illustrating the capabilities of the instrument and data analysis system have been obtained from rocket AKD-VB-27 which was launched from the Churchill Research Range, 20 January 1971.     

A solar radio spectrograph with high time resolution

Instrumentation for obtaining high time resolution dynamic spectra of solar radio bursts at decimetric wavelengths is described. The spectrograph sweeps the frequency range of 565–1000 MHz at a rate of 100 times per second. All data are recorded both on film and as an analog signal on magnetic tape. The frequency and flux calibrations are discussed. A sampling system which allows the activity at three discrete frequencies to be plotted on a chart recorder is described.     

A search for high energy gamma-rays from solar active regions

The Elliot model for solar flares predicts weak -ray emission from the flare region prior to large flares. A search has been made for such -radiation of energy > 50 MeV. The experiment was performed using balloon-borne detectors flown from an equatorial station during the 1967/1968 solar maximum. A number of small flares were observed, but no associated -rays were detected. A limit of 2.3 × 10⁴ photons/cm² s was placed on the emission from an importance 1N flare. The general lack of major solar activity during the period of the balloon flights precluded a test for the Elliot model.     

Two simple image slicers for high resolution spectroscopy

We present the design, manufacturing, test and performance of two image slicers for high resolution spectroscopy. Based on the classical Bowen-Walraven concept, our slicers allow to make two slices of the image of the input fibre. We introduce the idea of a second fibre that can be cropped in half to reach the same width of the science target fibre and that can be used for simultaneous wavelength reference. The slicers presented are mirror and prism based, respectively. Both devices work within expectation, showing differences mainly in their efficiency. The prism based slicer is the solution that was adopted for the FIDEOS spectrograph, an instrument built by the AIUC for the ESO 1m telescope of La Silla. Test spectra obtained with this instrument are included as examples of a real application of the device.     

A simple graphical solution for rocket wake boundaries

Assuming a simple conical ‘aerodynamic’ wake extending downstream from any point on the surface of a sounding rocket of typical configuration, equations are given to calculate whether a boom-mounted probe is within the wake, for varying wake angles. The calculation is straightforward for wake angles 0° and 90°. For the general case, as an alternative to solving quartic equations, a simple graphical method of solution is provided, affording quick solutions in generalized coordinates applicable to a wide range of rocket and boom configurations.     

A new concept and a preliminary design for a high resolution (HR) and very‐high resolution (VHR) spectrograph for the LBT

A way to fully exploit the large collecting area of modern 8–10m class telescopes is high resolution spectroscopy. Many astrophysical problems from planetary science to cosmology benefit from spectroscopic observations at the highest resolution currently achievable and would benefit from even higher resolutions. Indeed in the era of 8–10m class telescopes no longer the telescope collecting area but the size of the beam – which is related to the maximum size in which reflection gratings are manufactured – is what mainly limits the resolution. A resolution‐slit product R_φ ≃ 40,000 is the maximum currently provided by a beam of 20 cm illuminating the largest grating mosaics. We present a conceptual design for a spectrograph with R_φ ≃ 80,000, i.e. twice as large as that of existing instruments. Examples of the possible exploitation of such a high R_φ value, including spectropolarimetry and very high resolution (R ∼ 300,000), are discussed in detail. The new concept is illustrated through the specific case of a high resolution spectropolarimeter for the Large Binocular Telescope.     

A radiation belt monitor for the high energy transient experiment satellite

A Radiation Belt Monitor (RBM) sensitive to protons and electrons with energy 0.5 MeV¹ has been designed for the High Energy Transient Experiment (HETE) satellite in order to: first, control the on-off configuration of the experiments (i.e. those susceptible to proton damage); and second, to indicate the presence of proton and/or electron events that could masquerade as legitimate high energy photon events. One of the two RBM channels has an enhanced sensitivity to electrons. Each channel of the RBM, based on a PIN silicon diode, requires a typical power of 6 milliwatts. Tests have been performed with protons with energies from 0.1 to 2.5 MeV (generated by a Cockcroft-Walton linear accelerator via the d(d,p)t reaction), and with electrons with energies up to 1 MeV (from a 1.0 µCi²⁰⁷Bi source).     

A low resolution map of Europa from four occultations by Io

Analysis of three occultations of JII (Europa) by JI (Io) has resulted in a preliminary reflectivity map of JII for the hemisphere centered on longitude 324°, a measurement of 1483±20 km for the radius of JII, estimates of the event impact parameters, determination of the mid event times, and a visual geometric albedo, p_ν = 0.74, for JII. A fourth occultation light curve was used after derivation of the results to confirm their validity.     

A multibeam antenna for solar MM-wave burst observations with high spatial and temporal resolution

In this paper a new method for the determination of the position of microwave burst sources on the Sun, its implementation and first observational results, are presented. The 13.7 m antenna at Itapetinga with a five-channel receiver operating at 48 GHz and with a time resolution of 1 ms is used. Five horn antennas clustered around the focus of the Cassegrain reflector provide 5 beams diverging by about 2. This configuration allows the observation of different parts of an active region and the determination of the center of the burst position with an accuracy of 5 to 20 depending on the angular distance relative to the antenna axis. The field of view is 2 by 4. The time resolution of 1 ms is suitable to search for fast structures at 48 GHz. A total bandwidth of 400 MHz is used in order to achieve a sensitivity of 0.04 s.f.u. sufficient for the detection of weak bursts. First observational results of the flare on May 11, 1991 show a well-located source position during all stages.Paper presented at the 4th CESRA workshop in Ouranopolis (Greece) 1991.     

Instrumentation for very high energy gamma-ray astronomy

Considerable progress has been made in the last half-decade in the field of very high energy (VHE) gamma-ray astronomy (photons with energies between 10¹¹ and 10¹³ eV). The high background level due to the isotropic cosmic ray flux which has bedevilled the field since its inception in the early 1960's can now be reduced to such a degree that significant gamma-ray signals from several sources become visible within a few hours of observation. The instrumentation and methodologies which have made this possible are reviewed. A brief historical introduction is followed by a summary of the salient properties of the atmospheric Cherenkov flash associated with VHE gamma-ray events. The major components of a VHE gamma-ray astronomy telescope are then reviewed. This is followed by a discussion of the different methodologies currently being used to discriminate against the cosmic ray background. Properties of several specific installations are then summarized, and possible future developments in VHE instrumentation are briefly discussed.     

A high resolution mid-infrared image of the Starburst Galaxy M82

We have produced high-resolution images of the nuclear region of M82 with SpectroCam-10, a mid-infrared instrument at the Palomar 5 m telescope. These images were taken at 11.7 m and 9.8 m with a 1m filter bandpass at the diffraction limit of 0.6 arcsec, making them the highest resolution maps yet available of M82. In addition, we have obtained high-resolution (/=2000) maps of the velocity field of the nuclear disk of M82 in the 12.81 m line emission of [NeII]. In these proceedings we present the 11.7 m image, which will appear together with the 9.8 m map and the [Ne II] spectra in a subsequent paper, now in preparation. This image shows very clearly a bridge structure joining the eastern and western clusters.