The time behavior of temperature and emission measure in X-ray flares

Milkey, R. W.; Blocker, N.K.; Chambers, William H.; Fehlau, P.E.; Fuller, J.C.; Kunz, W.E.

doi:10.1007/bf00159772

Cited by 16 publications

(7 citation statements)

References 10 publications

(6 reference statements)

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“…In the events studied, the high temperature component peaks before maximum flux is attained whereas the corresponding emission measure rises more slowly before decaying. Similar observations have been made by previous authors (Kahler et al, 1970;Milkey et al, 1971 ;Horan, 1971) and…”

Section: Interpretation Of Observationssupporting

confidence: 92%

The thermal nature of soft X-ray flares

Craig

1973

Sol Phys

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Soft X-ray flare data in the wavelength range 2.6-10 A are used to examine the time variation of emission measure and electron temperature. The thermal plasma parameters were derived according to a two-temperature model proposed by Herring and Craig (1973). Estimates of electron density and source volume are made by assuming conductive and radiative cooling mechanisms. It is suggested that the present observations imply a multi-thermal interpretation of the soft X-ray flare.

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Section: Interpretation Of Observationssupporting

confidence: 92%

The thermal nature of soft X-ray flares

Craig

1973

Sol Phys

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“…The indicated errors in the temperature and emission measure values reflect count-rate statistics, and were determined in the least-squares analysis mentioned earlier. The time variations of temperature and emission measure illustrated here confirm earlier broad-band studies in which the temperature maximum has been found to precede that of the emission measure by several minutes (Kahler et al, 1970;Milkey et al, 1971 ;Horan, 1971). Kahler et al have noted two occasions when the emission measure in fact showed no significant decrease before the flare faded to background.…”

Section: Observational Datasupporting

confidence: 89%

Ionization equilibrium in soft X-ray-emitting solar flares

1974

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Studies of the flare-produced line feature at 1.9 A due to highly ionized iron show that it is emitted in conditions closely approximating steady-state ionization equilibrium. Calculations of the line flux per unit emission measure from time-dependent and steady-state ionization equilibria are compared with observed values during four flares in particular. Only for electron densities Ne~ 10 TM cm -3 do the time-dependent equilibrium values give as good an approximation to the observed values as the steady-state equilibrium. This lower limit is compared with values of Are derived from analyses of the temperature decline in each of these events, and with estimates of Are given by other workers.

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“…11 x 10 6 K. Figure 6, which assumes an emission measure of 10 48 cm-3, indicates that the maximum flux of Fe II-XX Ka lines is 60 photons cm -2 S -1, SO that the emission measure for this event is no less than 104Sx 2 • 104/6-~3 • 1051 cm -3. Such a value is considerably higher than those obtained in broadband continuum studies of the time behavior of temperature and emission measure during several flares Milkey et al, 1971). However, supporting evidence for the emission measure we obtain here is provided by an unpublished study of the 1-3 A continuum of the same flare made by Saba (1972).…”

Section: K~ Emission During Thermal Eventsmentioning

confidence: 58%

“…Soft X-ray events follow the hard impulsive bursts referred to earlier, last for some 3-70 rain, and exhibit temperatures as high as 2 or 3 x 107K (Neupert et al, 1969;Kahler et al, 1970;Milkey et al, 1971). At T= 3 x 107 K, 14% of electrons have energies in excess of the K-shell ionization potential of neutral iron which is 7.12 keV.…”

Section: K~ Emission During Thermal Eventsmentioning

confidence: 90%

K? line emission during solar X-ray bursts

Phillips

Neupert

1973

Sol Phys

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Kct X-ray line emission from S, Ar, Ca and Fe is calculated for conditions likely to exist in solar flares. We consider both the non-thermal and thermal phases of flares as indicated by X-ray observations. Impulsive non-thermal events seen at the onset of a flare at photon energies > 20 keV generally give rise to small Kc~ line fluxes (< 250 photons cm -z s -1-) on the basis of data presented by Kane and Anderson. The amount of S Kc~ radiation in particular depends sensitively on the lowerenergy bound of the non-thermal electron distribution giving rise to the impulsive burst, offering a possible means of determining this. Thermal Kc~ emission is significant for only Fe ions. For S, Ar and Ca, the temperatures required for a sizeable number of electrons with energies greater than the K-ionization potential will also strip these elements to ionization stages too high for Kc~ transitions to be possible. Comparison of thermal Kc~ emission from iron during an intense solar flare leads to a very high emission measure on the basis of these calculations, but such a value seems to be compatible with an analysis of the I-3 2t continuum during the same event.

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The time behavior of temperature and emission measure in X-ray flares

Cited by 16 publications

References 10 publications

The thermal nature of soft X-ray flares

The thermal nature of soft X-ray flares

Ionization equilibrium in soft X-ray-emitting solar flares

K? line emission during solar X-ray bursts

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