Electron Temperature and Emission Measure Determinations of Very Faint Solar Flares

1996 ◽  
Vol 461 ◽  
pp. 465 ◽  
Author(s):  
U. Feldman ◽  
G. A. Doschek ◽  
W. E. Behring
Keyword(s):  
Electron Temperature ◽  
Solar Flares ◽  
Emission Measure

Electron Temperature, Emission Measure, and X-Ray Flux in A2 to X2 X-Ray Class Solar Flares

1996 ◽  
Vol 460 ◽  
pp. 1034 ◽  
Author(s):  
U. Feldman ◽  
G. A. Doschek ◽  
W. E. Behring ◽  
K. J. H. Phillips
Keyword(s):  
Electron Temperature ◽  
Solar Flares ◽  
Emission Measure ◽  
X Ray

Analysis of the differential emission measure distributions for solar flares observed by RESIK

2018 ◽  
Vol 179 ◽  
pp. 545-552
Author(s):  
A. Kepa ◽  
B. Sylwester ◽  
J. Sylwester ◽  
M. Gryciuk ◽  
M. Siarkowski
Keyword(s):  
Solar Flares ◽  
Emission Measure ◽  
Differential Emission Measure

Plasma Diagnostics of Microflares observed by STIX and AIA

2021 ◽  
Author(s):  
Jonas Saqri ◽  
Astrid Veronig ◽  
Ewan Dickson ◽  
Säm Krucker ◽  
Andrea Francesco Battaglia ◽  
...  
Keyword(s):  
Solar Flares ◽  
Magnetic Energy ◽  
Emission Measure ◽  
Transport Processes ◽  
X Rays ◽  
Solar Dynamics Observatory ◽  
Energy Bands ◽  
Accurate Analysis ◽  
Great Opportunity ◽  
Wide Range

<p>Solar flares are generally thought to be the impulsive release of magnetic energy giving rise to a wide range of solar phenomena that influence the heliosphere and in some cases even conditions of earth. Part of this liberated energy is used for particle acceleration and to heat up the solar plasma. The Spectrometer/Telescope for Imaging X-rays (STIX) instrument onboard the Solar Orbiter mission launched on February 10th 2020 promises advances in the study of solar flares of various sizes. It is capable of measuring X-ray spectra from 4 to 150 keV with 1 keV resolution binned into 32 energy bins before downlinking. With this energy range and sensitivity, STIX is capable of sampling thermal plasma with temperatures of≳10 MK, and to diagnose the nonthermal bremsstrahlung emission of flare-accelerated electrons. During the spacecraft commissioning phase in the first half of the year 2020, STIX observed 68 microflares. Of this set, 26 events could clearly be identified in at least two energy channels, all of which originated in an active region that was also visible from earth. These events provided a great opportunity to combine the STIX observations with the multi-band EUV imagery from the Atmospheric Imaging Assembly (AIA) instrument on board the earth orbiting Solar Dynamics Observatory (SDO). For the microflares that could be identified in two STIX science energy bands, it was possible to derive the temperature and emission measure (EM) of the flaring plasma assuming an isothermal source. For larger events where more detailed spectra could be derived, a more accurate analysis was performed by fitting the spectra assuming various thermal and nonthermal sources. These results are compared to the diagnostics derived from AIA images. To this aim, the Differential EmissionMeasure (DEM) was reconstructed from AIA observations to infer plasma temperatures and EM in the flaring regions. Combined with the the relative timing between the emission seen by STIX and AIA, this allows us to get deeper insight into the flare energy release and transport processes.</p>

The 1 1S-n 1 P/1 1S-2 1 P emission-line ratios in SI XIII as electron temperature diagnostics for solar flares and active regions

1990 ◽  
Vol 363 ◽  
pp. 310 ◽  
Author(s):  
F. P. Keenan ◽  
S. M. McCann ◽  
K. J. H. Phillips
Keyword(s):  
Emission Line ◽  
Electron Temperature ◽  
Solar Flares ◽  
Active Regions ◽  
Temperature Diagnostics

The Electron Temperature and Fine Structure of Soft X‐Ray Solar Flares

1999 ◽  
Vol 527 (1) ◽  
pp. 426-434 ◽  
Author(s):  
G. A. Doschek
Keyword(s):  
Fine Structure ◽  
Electron Temperature ◽  
Solar Flares ◽  
X Ray

scholarly journals The Temperature Structure of NGC 7027

1989 ◽  
Vol 131 ◽  
pp. 176-176
Author(s):  
C. T. Daub ◽  
J. P. Basart
Keyword(s):  
Temperature Distribution ◽  
Electron Temperature ◽  
Angular Resolution ◽  
Hot Spot ◽  
Emission Measure ◽  
The Other ◽  
Radio Continuum ◽  
Line Of Sight ◽  
Temperature Structure ◽  
Ngc 7027

Radio maps of the free-free radio continuum flux (angular resolution ≅ 1.3 arcseconds) from NGC 7027 were made with the VLA operating at 20-cm, 6-cm, and 2-cm wavelengths which are near and straddle unit optical depth. Mean line-of-sight electron temperature and emission measure distributions were calculated by pairing the 2-cm and 6-cm maps, and the electron temperature distribution on the near side of the nebula was then obtained from the 20-cm map. The results suggest that the energy balance is complex in this planetary. For example, mean line-of-sight temperatures are higher than average in the direction of one of the bright lobes but not in the direction of the other. Especially noteworthy is an apparent “hot spot” on the near side of the nebula which has no apparent relation to either of the bright lobes, but it is approximately coincident with the brightest portion of the optical image.

scholarly journals Thermal-nonthermal energy partition in solar flares derived from X-ray, EUV, and bolometric observations

2020 ◽  
Vol 644 ◽  
pp. A172
Author(s):  
A. Warmuth ◽  
G. Mann
Keyword(s):  
Solar Flares ◽  
Energy Transport ◽  
Emission Measure ◽  
Energy Partition ◽  
Thermal Component ◽  
Additional Energy ◽  
Radiated Energy ◽  
Sufficient Energy ◽  
Energy Cutoff ◽  
Nonthermal Particles

Context. In solar flares, energy is released impulsively and is partly converted into thermal energy of hot plasmas and kinetic energy of accelerated nonthermal particles. It is crucial to constrain the partition of these two energy components to understand energy release and transport as well as particle acceleration in solar flares. Despite numerous efforts, no consensus on quantifying this energy balance has yet been reached. Aims. We aim to understand the reasons for the contradicting results on energy partition obtained by various recent studies. The overarching question we address is whether there is sufficient energy in nonthermal particles to account for the thermal flare component. Methods. We considered five recent studies that address the thermal-nonthermal energy partition in solar flares. Their results are reviewed, and their methods are compared and discussed in detail. Results. The main uncertainties in deriving the energy partition are identified as (a) the derivation of the differential emission measure distribution and (b) the role of the conductive energy loss for the thermal component, as well as (c) the determination of the low-energy cutoff for the injected electrons. The bolometric radiated energy, as a proxy for the total energy released in the flare, is a useful independent constraint on both thermal and nonthermal energetics. In most of the cases, the derived energetics are consistent with this constraint. There are indications that the thermal-nonthermal energy partition changes with flare strength: in weak flares, there appears to be a deficit of energetic electrons, while the injected nonthermal energy is sufficient to account for the thermal component in strong flares. This behavior is identified as the main cause of the dissimilar results in the studies we considered. The changing partition has two important consequences: (a) an additional direct (i.e. non-beam) heating mechanism has to be present, and (b) considering that the bolometric emission originates mainly from deeper atmospheric layers, conduction or waves are required as additional energy transport mechanisms.

scholarly journals Optical HII regions

1979 ◽  
Vol 84 ◽  
pp. 65-72 ◽  
Author(s):  
Y. M. Georgelin ◽  
Y. P. Georgelin ◽  
J.-P. Sivan
Keyword(s):  
Electron Temperature ◽  
Spiral Galaxies ◽  
Emission Measure ◽  
Hii Regions ◽  
Nuclear Region ◽  
Diffuse Emission

The ionized hydrogen regions seen on monochromatic Hα photographs of nearby spiral galaxies (e.g. Fig. 1) can be divided into four classes (Monnet, 1971): (1) bright, condensed, classical HII regions; (2) diffuse emission in the arms surrounding and connecting the classical regions (emission measure (EM) ∼ 150 cm−6 pc, for a gas electron temperature of 6000 K); (3) much fainter, diffuse emission extending over the entire disk (EM ∼ 50 cm−6 pc) in most Sc and Sd galaxies; (4) diffuse emission in the nuclear region.

scholarly journals Post-flare Coronal Activity on AU Mic Detected by EUVE

1995 ◽  
Vol 151 ◽  
pp. 146-147
Author(s):  
Maria Katsova ◽  
Jeremy Drake ◽  
Moissei Livshits
Keyword(s):  
Solar Flares ◽  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Coronal Loops ◽  
Stellar Radius ◽  
Euv Emission ◽  
Long Duration ◽  
Red Dwarfs ◽  
Coronal Activity ◽  
Region Scale

Data of long-duration emission arising after the impulsive rise and decay in a flaring event on the red dwarf star AU Mic are discussed. Intensive EUV emission in the band 65-190 Å was registered by the Extreme Ultraviolet Explorer (EUVE) after both impulses during half a day. A similar behavior of the flux in the Fe XVIII 93.9 Å line is detected after the first powerful impulse. The decay of the intensity in the 65-190 Å band and in the Fe XVIII line during this prolonged event is 10 times slower than the time of radiative cooling of coronal loops with a typical flare plasma density. Some difficulties with two explanations of this event proposed earlier are discussed. Explanation (i) - the radiation of dense loops at main phase of the flare, and (ii) - the emission of the low-dense plasma of coronal transients (CME). The temporal behavior of the emission measure is determined for both the 65-190 Å band and the Fe XVIII line fluxes. The total energy emitted in the 1-2000 Å region for the long-duration event lasting almost 12 hours is 3 · 1035 ergs. The following physical model is proposed to explain the prolonged event (Fig. 1): the source of emission is the system of high coronal loops, the size of which is more than the active region scale, but is less than the stellar radius. The temperature of the plasma in the loops decreases from 107 K slowly, during a few hours. The densities in these loops are in the range 1013 cm−3 to 5 · 109 cm−3. Such systems, when the plasma therein becomes cool, are observed in the Hα line during large solar flares (for instance, June 15, 1991) after CME. Some additional post-flare energy input into this high coronal loop systems can be caused by the reconnection in vertical current sheet, and this post-eruptive energy release provides prolonged and intensive EUV emission.Apparently, we are faced here with a new kind of surface activity on late-type stars which is intermediate between impulsive flares on red dwarfs and long-duration, powerful events on subgiants, which are components of RS CVn binaries.The full version of this contribution will be published in Astronomicheskij Zhurnal (Astronomy Reports), 1995, Vol. 72.

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