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  • 1
    Electronic Resource
    Electronic Resource
    Isotropic Gamma-ray Intensity in an Expanding Universe (1967)
    [s.l.] : Nature Publishing Group
    Nature 215 (1967), S. 1035-1038 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The intensities of isotropic gamma-rays produced by the inverse Compton process in an expanding universe are calculated, including the effect of red-shift on the radiation field. The results may give information concerning the universal black-body radiation field and the intergalactic electron flux ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/2151035a0
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  • 2
    Electronic Resource
    Electronic Resource
    Rayleigh-taylor instability in solar prominences as a mechanism for dXouble-ribbon flares
    Amsterdam : Elsevier
    Chinese Astronomy and Astrophysics 7 (1983), S. 1-5 
    Details
    ISSN: 0275-1062
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0275-1062(83)90022-X
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical studies of the flux and energy spectrum of gamma radiation from the Sun (1972)
    Springer
    Space science reviews 13 (1972), S. 3-123 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The purpose of this work is to study the various γ-ray-production mechanisms in solar flares and to calculate the flux, the spectrum, and the decay curves of γ radiation. Using the continuity equation and taking into account the energy losses for solar-flare-accelerated particles, we obtain the time-dependent particle distribution and thus the time behavior of the resulting γ rays. The important processes for producing γ rays in solar flares are found to be nonthermal electron bremsstrahlung, decay of neutral π mesons, positron annihilation, neutron capture, and decay of excited nuclei. The results are applied to several known solar flares. For a large flare such as the class 3+ on February 23, 1956, continuous γ rays with energies up to 100 MeV from electron bremsstrahlung and neutral π meson decays are observable at the orbit of the Earth by existing γ-ray detectors. Line γ rays from positron annihilation (0.51 MeV), neutron capture (2.23 MeV), and deexcitation of excited nuclei O16 (6.14 and 7.12 MeV) and C12 (4.43 MeV) are particularly strong and well above the continuous γ-ray background due to electron bremsstrahlung. These lines can be detected at the Earth.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198165
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  • 4
    Electronic Resource
    Electronic Resource
    The gradual and impulsive reconnection and the preheating of solar flares (1987)
    Springer
    Solar physics 107 (1987), S. 271-282 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss the preheating phase of solar flares triggered by emerging magnetic flux. We consider the development of microinstabilities in the diffusion region during the emergence process and we propose four different types of reconnection, by which we explain the preheating, as well as the impulsive phase of flares. We find that during the emergence of new magnetic flux the current sheet will not ‘jump’ from the initial classical state to a fully turbulent one, but will remain in a marginally turbulent state which may develop either gradually or impulsively depending on the conditions of emergence. As a consequence of this, we find that four cases of reconnection are indeed possible: a week gradual heating, a weak impulsive process, a gradual preheating followed by an impulsive phase, and violent bursty reconnection. The expansion rate of the diffusion region, the duration of the gradual phase, the magnetic energy release, and the energy deposition rate in coronal loops during the gradual phase are derived under simplifying assumptions and applied to X-ray and UV observations of flares from the Solar Maximum Mission.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152025
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  • 5
    Electronic Resource
    Electronic Resource
    Densities and mass motions in transition-zone plasmas in solar flares observed from Skylab (1980)
    Springer
    Solar physics 65 (1980), S. 283-298 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We studied the EUV line spectra of three flare observed with the NRL slit spectrograph on Skylab. The electron densities in the flare transition-zone plasmas are determined from density-sensitive lines of Si iii and O iv. The electron densities in all three flares studied were greatest during the flare maximum with values of the order of 1012 cm−3. The density decreases by a factor of 2 to 3 in the decay phase of the flares. The intensities of EUV lines from the flare chromospheric and transition-zone plasmas all are greatly enhanced. In contrast to lines for Oi, Ci, Feii and other chromospheric ions, the lines of Oiv and Nv and other transition-zone lines are not only enhanced but also very much broadened. Fitting of the N v 1242 Å line with a two-gaussian model shows that for two of the flares studied, there is a red-shifted component in addition to an unshifted component. The shifted component in the N v line profiles is interpreted as due to a dynamic and moving plasma with a bulk motion velocity of 12 km s−1 for one flare and more than 70 km s−1 for the other. The broadened line profiles indicate that there are large turbulent mass motions with random velocities ranging from 30 to 80 km s−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152795
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  • 6
    Electronic Resource
    Electronic Resource
    Spatial distribution of XUV emission and density in a loop prominence (1980)
    Springer
    Solar physics 65 (1980), S. 347-356 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the spatial distribution of XUV emission in the 14 August, 1973 loop prominence observed with the NRL spectroheliograph on Skylab. The loop prominence consists of two large loops and is observed in lines from ions with temperatures ranging from 5 × 104 K to 3 × 106 K. The loops seen in low temperature (≲106K) lines such as from He ii, Ne vii, Mg vii, Mg viii, and Si viii are systematically displaced from loops seen in higher temperature lines such as from Si xii, Fe xv, and Fe xvi. The cross section of the loop, particularly in cooler lines is nearly constant along the loop. For hotter loops in Si xii, Fe xv, and Fe xvi, however, emission at the top of the loop is more intense and extended than that near the footpoints, which makes the loops appear wider at the top. There is no evidence that the 14 August loop prominence consists of a cooler core surrounded by a hot sheath as in some active region and sunspot loops reported by Foukal (1975, 1976). Rather, the observed spatial displacement between cooler and hotter loops suggest that the 14 August loop prominence is composed of many magnetic flux tubes, each with its own temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152798
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  • 7
    Electronic Resource
    Electronic Resource
    Emission measures and structure of the transition region of a sunspot from emission lines in the far ultraviolet (1977)
    Springer
    Solar physics 52 (1977), S. 327-335 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Absolute intensities of emission lines in the wavelength range from 1200 Å to 1817 Å from the large sunspot in McMath region 12510 near Sun center are presented. The intensities are averaged across the umbra and penumbra of the sunspot. The observations were made with the NRL slit spectrograph on Skylab. Emission measures are derived from the measured intensities. Assuming a balance between the divergence of the conductive energy flux and the radiative energy losses, a self-consistent model of the lower transition region in the sunspot is constructed. The model gives a constant pressure of about 0.19 dyne cm-2, and a conductive flux which decreases approximately one order of magnitude between 2 × 105 K and 4 × 104 K. The temperature gradient is relatively constant, increasing slowly with decreasing temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149649
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  • 8
    Electronic Resource
    Electronic Resource
    Evolution of the high-temperature plasma in the 15 June 1973 flare (1977)
    Springer
    Solar physics 55 (1977), S. 413-419 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The analysis of the high temperature plasma in Fe xxiii–xxiv in the 15 June 1973 flare is presented. The observations were obtained with the NRLXUV spectroheliograph on Skylab. The results are: (1) There was preheating of the active region in which the flare occurred. In particular, a large loop in the vicinity of the flaring region showed enhanced brightness for many hours before the flare. The loop disappeared when the flare occurred, and returned in the postflare phase, as if the energy flux which had been heating the large loop was blocked during the flare and restored after the flare was gone. The large magnetic fields did not change significantly. (2) The flare occurred in low-lying loop or loops. The spatial distribution of flare emission shows that there was a temperature gradient along the loop. (3) The high temperature plasma emitting Fe xxiii and xxiv had an initial upward motion with a velocity of about 80 km s−1. (4) There was large turbulent mass motion in the high temperature plasma with a random velocity of 100 to 160 km s−1. (5) The peak temperature of the hot plasma, determined from the Fe xxiii and xxiv intensity ratio, was 14 × 106 K. It decreased slightly and then, for a period of 4 min, remained at 12.6 × 106 K before dropping sharply to below 10 × 106 K. The density of the central core of the hot plasma, determined from absolute intensity of Fe xxiv 255 Å line, was of the order of 1011 cm−3. The persistence of the high level of turbulence and of the high temperature plateau in the decaying phase of the flare indicates the presence of secondary energy release. From the energy balance equation the required energy source is calculated to be about 3 to 7 ergs cm−3 s−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00152584
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  • 9
    Electronic Resource
    Electronic Resource
    The EUV continuum emission (1400–1960 Å) in a solar flare observed from Skylab (1978)
    Springer
    Solar physics 59 (1978), S. 361-371 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The total radiative output in the EUV continuum (1400–1960 Å) from the 5 September 1973 flare has been obtained from the EUV spectra of the flare observed with the NRL slit spectrograph (SO82B) on Skylab. The radiative energy in the EUV continuum is of the order of 1029 ergs, which is more than a factor of 2 greater than those radiated in soft X-rays (8–20 Å) and in Hα for the flare. Thus, the EUV continuum emission is an important radiative energy loss, and should be included in the consideration of the energy balance of the flare.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00951841
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  • 10
    Electronic Resource
    Electronic Resource
    Morphology and spatial distribution of XUV and X-ray emissions in an active region observed from Skylab (1980)
    Springer
    Solar physics 67 (1980), S. 259-265 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We studied the morphology and spatial distribution of loops in an active region, using coordinated observations obtained with both the S082A XUV spectroheliograph and the S056 grazingincidence X-ray telescope on Skylab. The active region loops in the temperature range 5 × 105 −3 × 106 K fall basically into two distinctive groups: the hot loops with temperatures 2–3 × 106 K as observed in coronal lines and X-rays, and the relatively cool loops with temperature 5 × 105 −1 × 106 K as observed in transition-zone lines (Ne vii, Mg ix). The brightest hot coronal loops in the active region are mostly low-lying, compact, closely-packed, and show greater stability than the transition-zone loops, which are fewer in number, large, and slender. The observed aspect ratio of the hot coronal loops is in the range of 0.1 and 0.2, which are almost two orders of magnitude larger than those for the Ne vii loops. Brief discussion of the MHD stability of the loops in terms of the aspect ratio is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00149806
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