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  • 1
    Electronic Resource
    Electronic Resource
    HINOTORI - a Japanese satellite for solar flare studies
    Amsterdam : Elsevier
    Advances in Space Research 2 (1982), S. 201-202 
    Details
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0273-1177(82)90200-9
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  • 2
    Electronic Resource
    Electronic Resource
    Microwave and Soft X-ray Study of Solar Active Region Evolution (1998)
    Springer
    Solar physics 178 (1998), S. 353-378 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the properties and evolution of several active regions observed at multiple wavelengths over a period of about 10 days. We have used simultaneous microwave (1.5 and 17 GHz) and soft X-ray measurements made with the Very Large Array (VLA), the Nobeyama Radio Heliograph (NRH) and the Soft X-ray Telescope (SXT) on board the Yohkoh spacecraft, as well as photospheric magnetograms from KPNO. This is the first detailed comparison between observations at radio wavelengths differing by one order of magnitude. We have performed morphological and quantitative studies of active region properties by making inter-comparison between observations at different wavelengths and tracking the day-to-day variations. We have found good general agreement between the 1.5 and 17 GHz radio maps and the soft X-rays images. The 17 GHz emission is consistent with thermal bremsstrahlung (free-free) emission from electrons at coronal temperatures plus a small component coming from plasma at lower temperatures. We did not find any systematic limb darkening of the microwave emission from active regions. We discuss the difference between the observed microwave brightness temperature and the one expected from X-ray data and in terms of emission of a low temperature plasma at the transition region level. We found a coronal optical thickness of ∼ 10-3 and ∼ 1 for radiation at 17 and 1.5 GHz, respectively. We have also estimated the typical coronal values of emission measure (∼ 5 × 1028 cm-5), electron temperature (∼ 4.5 × 1066 K) and density (∼ 1.2 × 109 cm3). Assuming that the emission mechanism at 17 GHz is due to thermal free-free emission, we calculated the magnetic field in the source region using the observed degree of polarization. From the degree of polarization, we infer that the 17 GHz radiation is confined to the low-lying inner loop system of the active region. We also extrapolated the photospheric magnetic field distribution to the coronal level and found it to be in good agreement with the coronal magnetic field distribution obtained from microwave observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004982902622
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  • 3
    Electronic Resource
    Electronic Resource
    Successive electron and ion accelerations in impulsive solar flares on 7 and 21 June 1980 (1983)
    [s.l.] : Nature Publishing Group
    Nature 305 (1983), S. 292-294 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The time profiles of the impulsive burst on 7 June are shown in Fig. 1. The burst is composed of seven successive pulses of a quasiperiodicity of 8 s, for each of which the hard X-ray, ?-ray and microwave emissions were observed almost simultaneously1"6. Hard X-ray and ?-ray observations were made ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/305292a0
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  • 4
    Electronic Resource
    Electronic Resource
    Energy transport and dynamics (1994)
    Springer
    Solar physics 153 (1994), S. 55-72 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report findings concerning energy transport and dynamics in flares during the impulsive and gradual phases based on new ground-based and space observations (notably fromYohkoh). A preheating sometimes occurs during the impulsive phase. Caxix line shifts are confirmed to be good tracers of bulk plasma motions, although strong blue shifts are not as frequent as previously claimed. They often appear correlated with hard X-rays but, forsome events, the concept that electron beams provide the whole energy input to the thermal component seems not to apply. Theory now yields: new diagnostics of low-energy proton and electron beams; accurate hydrodynamical modeling of pulse beam heating of the atmosphere; possible diagnostics of microflares (based on X-ray line ratio or on loop variability); and simulated images of chromospheric evaporation fronts. For the gradual phase, the continual reorganization of magnetic field lines over active regions determines where and when magnetic reconnection, the mechanism favoured for energy release, will occur. Spatial and temporal fragmentation of the energy release, observed at different wavelengths, is considered to be a factor as well in energy transport and plasma dynamics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712492
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  • 5
    Electronic Resource
    Electronic Resource
    Simultaneous high spatial resolution observations of solar flares in X-rays and microwaves (review) (1982)
    Springer
    Solar physics 113 (1982), S. 49-56 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Results of simultaneous high-resolution microwave and X-ray two-dimensional imaging observations are briefly reviewed. It is shown that seven events published in the literature are not homogeneous but rather diverse with respect to spatial structure, mutual relations on position or shape. An outlook is presented for the next solar cycle to obtain a large data set for extensive study of energetic solar phenomena.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00147681
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  • 6
    Electronic Resource
    Electronic Resource
    Particle acceleration in flares (1994)
    Springer
    Solar physics 153 (1994), S. 33-53 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Particle acceleration is intrinsic to the primary energy release in the impulsive phase of solar flares, and we cannot understand flares without understanding acceleration. New observations in soft and hard X-rays, γ-rays and coherent radio emissions are presented, suggesting flare fragmentation in time and space. X-ray and radio measurements exhibit at least five different time scales in flares. In addition, some new observations of delayed acceleration signatures are also presented. The theory of acceleration by parallel electric fields is used to model the spectral shape and evolution of hard X-rays. The possibility of the appearance of double layers is further investigated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00712491
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  • 7
    Electronic Resource
    Electronic Resource
    Long time delay between the peaks of intense solar hard X-ray and microwave bursts (1983)
    Springer
    Solar physics 89 (1983), S. 379-390 
    Details
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract It is shown that the long time delays more than five seconds between the peaks of intense hard X-ray and microwave bursts are concerned with two independent phenomena. One is the energy dependent time delays in X-rays and the other is the frequency dependent time delays in microwaves. The time delays of 5 s to 10 s between the peaks of solar hard X-ray burst (≲100 keV) obtained with Hinotori spacecraft and microwave burst at 17 GHz were observed exceptionally in three intense events with a spectral maximum at about 17 GHz. It is found that the peak of harder X-rays (≳300 keV) also delays in these events by about the same amount with respect to the softer X-rays (≲100 keV), so that the peak at 17 GHz nearly coincides (≲4s) with that of the harder X-rays. This is quite reasonable because the gyro-synchrotron emissions from the electrons below about 100 keV in the solar flares are generally negligible at high microwave frequencies (≳10 GHz). The optical thickness of the radio source decreases with frequency and is unity generally at about 10–20 GHz in intense bursts as inferred from the radio spectrum. Further delay of the peaks at the lower microwave frequencies is attributed to the temporal increase in the effective size of radio source which is optically thick at the lower frequencies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00217257
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  • 8
    Electronic Resource
    Electronic Resource
    Thermal and nonthermal flare emission observed with the Nobeyama Radio Heliograph (1994)
    Springer
    Space science reviews 68 (1994), S. 217-224 
    Details
    ISSN: 1572-9672
    Keywords: solar flares ; radio emission ; nonthermal particles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The early phases of three flares, observed by the Nobeyama Radio Heliograph, are studied. Nonthermal and thermal radio sources are identified by comparison with soft X-ray images taken by the Soft X-ray Telescope onboard the Yohkoh satellite. Two of the flares are mainly of nonthermal origin and their location coincides with one of the footpoints of soft X-ray loops. Another flare has both thermal and nonthermal components which start to brighten simultaneously. This suggests that particle acceleration and plasma compression develop simultaneously.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00749141
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