X-radiation (E > 10keV), Hα and microwave emission during the impulsive phase of solar flares |
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Authors: | Joan A Vorpahl |
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Institution: | (1) Space Sciences Laboratory, University of California, 94720 Berkeley, Calif., U.S.A.;(2) Present address: 721 Blackmer Circle, 95825 Sacramento, Calif., U.S.A. |
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Abstract: | A study has been made of the variation in hard (E 10 keV) X-radiation, H and microwave emission during the impulsive phase of solar flares. Analysis shows that the rise-time in the 20–30-keV X-ray spike depends on the electron hardness, i.e., t
rise exp (0.87 ). The impulsive phase is also marked by an abrupt, very intense increase in H emission in one or more knots of the flare. Properties of these H kernels include: (1) a luminosity several times greater than the surrounding flare, (2) an intensity rise starting about 20–30 s before, peaking about 20–25 s after, and lasting about twice as long as the hard spike, (3) an effective diameter of 3000–6000 km for class 1 flares, representing less than 1/8-1/2 of the main flare, (4) a location lower in the chromosphere than the remaining flare, (5) essentially no expansion prior to the hard spike, (6) a position within 6000 km of the boundary separating polarities, usually forming on both sides of the neutral line near both feet of the same tube of force, (7) a shape often resembling isogauss contours of the photospheric field indicated on magnetograms and (8) total radiated energy less than l/50 that of the hard electrons. Correspondingly, impulsive microwave events are characterized by: (1) the detection of a burst at 8800 MHz for every X-ray spike ifthe number of electrons above 100 keV is greater than 1033, (2) great similarity in burst structure with 20–32 keV X-rays but only at f > 5000 MHz, (3) typical low frequency burst cutoff between 1400–3800 MHz, and (4) maximum emission at f > 7500 MHz. Finally the H , X-ray and microwave data are combined to present a picture of the impulsive phase consistent with the above observations. |
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