Flaring Coronal Structures

1994 ◽  
Vol 144 ◽  
pp. 227-234
Author(s):  
T. Watanabe
Keyword(s):  
Solar Corona ◽  
Magnetic Reconnection ◽  
Time Scales ◽  
Solar Flares ◽  
Initial Phase ◽  
X Ray ◽  
Ionized Plasmas ◽  
First Time ◽  
Coronal Structures

AbstractThe highlights of the Japanese solar mission,Yohkoh, are presented, with emphasis on flaring structures in the solar corona. Definitive evidences of the magnetic reconnection in the solar corona are observationally confirmed for the first time. New insights in the location of hard X-ray sources are obtained. Completely blueshifted line emissions from highly ionized plasmas are seen at the very initial phase of solar flares. It is revealed that the solar corona is very dynamic in various time scales in X-ray intensities. Ample evidences of numerous flare-like activity like microflares and X-ray jets conclude that they are also the manifestation of the magnetic reconnection.

scholarly journals MHD Aspects of Coronal Transients

1980 ◽  
Vol 91 ◽  
pp. 263-277 ◽  
Author(s):  
U. Anzer
Keyword(s):  
Solar Corona ◽  
Time Scales ◽  
White Light ◽  
Solar Flares ◽  
Great Length ◽  
X Ray

If one defines coronal transients as events which occur in the solar corona on rapid time scales (≲ several hours) then one would have to include a large variety of solar phenomena: flares, sprays, erupting prominences, X-ray transients, white light transients, etc. Here we shall focus our attention on the latter two phenomena; solar flares have been discussed at great length in a recent Skylab workshop and IAU Colloqium No. 44 was devoted to the study of prominences. Coronal transients, in the narrower sense, were first seen with the instruments on board of Skylab, both in the optical and the X-ray part of the spectrum.

scholarly journals Statistical Properties of Magnetic Separators in Model Active Regions

2000 ◽  
Vol 195 ◽  
pp. 443-444
Author(s):  
B. T. Welsch ◽  
D. W. Longcope
Keyword(s):  
Active Region ◽  
Solar Corona ◽  
Magnetic Reconnection ◽  
First Principles ◽  
Magnetic Charge ◽  
Active Regions ◽  
Heating Rates ◽  
X Ray ◽  
Field Lines ◽  
Charge Topology

“Transient brightenings” (or “microflares”) regularly deposit 1027 ergs of energy in the solar corona, and account for perhaps 20% of the active corona's power (Shimizu 1995). We assume these events correspond to episodes of magnetic reconnection along magnetic separators in the solar corona. Using the techniques of magnetic charge topology, we model active region fields as arising from normally distributed collections of “magnetic charges”, point-like sources/sinks of flux (or field lines). Here, we present statistically determined separator (X-ray loop) lengths, derived from first principles. We are in the process of statistical calculations of heating rates due to reconnection events along many separators.

scholarly journals Hard X-ray Spectrum of the Above-the-Looptop Source in Impulsive Solar Flares

2000 ◽  
Vol 195 ◽  
pp. 413-414
Author(s):  
S. Masuda
Keyword(s):  
Magnetic Reconnection ◽  
Energy Release ◽  
Solar Flares ◽  
Count Rate ◽  
High Quality ◽  
X Ray ◽  
Flare Energy

Extended AbstractThe Hard X-ray Telescope (HXT: Kosugi et al. 1991) onboard Yohkoh has observed that, in impulsive solar flares, a hard X-ray source is located above the apex of a soft X-ray flaring loop, in addition to double footpoint sources (Masuda et al. 1994, 1995). This observation suggests that flare energy-release, probably magnetic reconnection, takes place not in the soft X-ray loop but above the loop. It is important to derive the hard X-ray spectrum of the above-the-looptop source accurately in order to understand how electrons are energized there. The above-the-looptop source was most clearly observed during the 13 January 1992 flare. However, the count rate, especially in the H-band (53–93 keV), is too small to synthesize high-quality images and to derive an accurate spectrum.

scholarly journals Observations of X-Ray Jets Using Yohkoh Soft X-Ray Telescope

1993 ◽  
Vol 141 ◽  
pp. 343-346
Author(s):  
K. Shibata ◽  
Y. Ishido ◽  
L. Acton ◽  
K. Strong ◽  
T. Hirayama ◽  
...  
Keyword(s):  
Time Series ◽  
Kinetic Energy ◽  
Solar Corona ◽  
Magnetic Reconnection ◽  
Typical Size ◽  
X Ray

AbstractTime series of SXT (Soft X-ray Telescope) images have revealed many jet-like features in the solar corona. Typical size of the “jet” is 5 × 103 – 4 × 105 km, the typical projected velocity is 30 – 300 km/s, and the kinetic energy estimated to be 1025 – 1028 erg. Many of the jets are associated with flare-like bright points or sub-flares. Three typical examples are discussed, including an X-ray jet identified with an Hα surge. It is suggested that magnetic reconnection is one of the possible mechanisms to produce these X-ray jets.

Observations from the Hinotori mission

1991 ◽  
Vol 336 (1643) ◽  
pp. 339-347 ◽  
Keyword(s):  
Solar Flares ◽  
Bragg Diffraction ◽  
High Dispersion ◽  
X Rays ◽  
Crystal Spectrometer ◽  
Quartz Crystals ◽  
X Ray ◽  
X Ray Imaging ◽  
Imaging Telescope ◽  
First Time

The satellite Hinotori was launched in 1981 by the Institute of Space and Astronautical Science of Japan. Two major experiments on board the Hinotori satellite were a hard X-ray imaging telescope with modulation collimators, and a high dispersion soft X-ray crystal spectrometer utilizing the Bragg diffraction of X-rays on quartz crystals. These two instruments have revealed for the first time that solar flares show varying characteristics depending on the environment of flaring regions, and that flares produce plasmas as hot as 3-4 x 10 7 K.

scholarly journals Quiescent Coronae of Active Chromosphere Stars

1983 ◽  
Vol 71 ◽  
pp. 83-108 ◽  
Author(s):  
Leon Golub
Keyword(s):  
Solar Corona ◽  
High Sensitivity ◽  
Model Atmosphere ◽  
Loop Model ◽  
X Rays ◽  
M Dwarfs ◽  
Coronal Emission ◽  
Dwarf Stars ◽  
X Ray ◽  
First Time

ABSTRACTThe EINSTEIN Observatory has for the first time provided high sensitivity X-ray measurements of quiescent coronal emission from a large sample of dwarf stars. We now have observed a sufficient number of the nearby M-dwarfs to determine an X-ray luminosity function and we have explored the activity and variability of these stars to the extent of observing, for the first time, X-ray flares with simultaneous groundbased optical and IUE ultraviolet coverage.The M dwarfs are found to have a much higher degree of variability in X-rays than does the Sun; however, in most cases a quiescent level is definable. We will discuss the quiescent emission from these stars and the changes in quiescent level on time scales from hours to ~ 1 year. We have determined coronal temperatures for many of these stars; they are generally hotter than the Solar corona and some of the more active dM stars have Tcor ~ 107 K.Arguments are presented in support of the hypothesis that M-dwarf coronae are magnetically dominated, as is the Solar corona. We then examine the usefulness of loop model atmosphere calculations in elucidating the coronal heating mechanism and the ways in which observations may be used to test competing theories. The X-ray measurements can be used to predict magnetic field strengths on these stars, with testable implications.

scholarly journals Hot X-ray onsets of solar flares

2020 ◽  
Vol 501 (1) ◽  
pp. 1273-1281
Author(s):  
Hugh S Hudson ◽  
Paulo J A Simões ◽  
Lyndsay Fletcher ◽  
Laura A Hayes ◽  
Iain G Hannah
Keyword(s):  
Solar Flares ◽  
Impulsive Phase ◽  
High Energy ◽  
Small Sample ◽  
X Ray ◽  
Isothermal Plasma ◽  
Modelling Techniques ◽  
Loop Regions ◽  
Collisional Heating ◽  
Coronal Structures

ABSTRACT The study of the localized plasma conditions before the impulsive phase of a solar flare can help us understand the physical processes that occur leading up to the main flare energy release. Here, we present evidence of a hot X-ray ‘onset’ interval of enhanced isothermal plasma temperatures in the range of 10–15 MK over a period of time prior to the flare’s impulsive phase. This ‘hot onset’ interval occurs during the initial soft X-ray increase and definitely before any detectable hard X-ray emission. The isothermal temperatures, estimated by the Geostationary Operational Environmental Satellite X-ray sensor, and confirmed with data from the Reuven Ramaty High Energy Solar Spectroscopic Imager, show no signs of gradual increase, and the ‘hot onset’ phenomenon occurs regardless of flare classification or configuration. In a small sample of four representative flare events, we tentatively identify this early hot onset soft X-ray emission to occur within footpoint and low-lying loop regions, rather than in coronal structures, based on images from the Atmospheric Imaging Assembly. We confirm this via limb occultation of a flaring region. These hot X-ray onsets appear before there is evidence of collisional heating by non-thermal electrons, and hence challenge the standard modelling techniques.

scholarly journals On the Thermal Interpretation of Hard X-Ray Bursts from Solar Flares

1974 ◽  
Vol 57 ◽  
pp. 395-412 ◽  
Author(s):  
John C. Brown
Keyword(s):  
Solar Flares ◽  
Thermal Conduction ◽  
Temperature Structure ◽  
X Rays ◽  
X Ray ◽  
Time Variations ◽  
Relationship Of ◽  
First Time ◽  
The Relationship ◽  
Continuous Temperature

The possible validity of thermal bremsstrahlung models of flare hard X-ray bursts is investigated quantitatively. In particular, the problem of rapid thermal conduction in ‘multi-temperature’ models is adequately examined for the first time by using a continuous temperature distribution consistent with the observed X-ray spectrum. This distribution is obtained from a general analytic solution for the temperature structure required to mimick any ‘non-thermal’ spectrum, the method being equally applicable to cosmic sources.It is concluded that the thermal interpretation might extend to X-rays of hundreds of keV, a result with important consequences for flare energetics. The relationship of such a model to observations of X-ray polarization and rapid time variations is also considered.

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