Strong coronal shocks and ‘thermal’ solar X-ray bursts |
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| Authors: | Charles L Hyder |
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| Institution: | (1) Sacramento Peak Observatory of the Air Force Cambridge Research Laboratories, UK |
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| Abstract: | I find that a one-dimensional strong coronal shock (M
s
 3) will grow outward until the Mach number (M
s
) ceases to increase with height (dM
s
/dh = 0). The shock is driven by the pressure gradient and it is damped by gravity and by energy losses (radiative and conductive). The driving and damping terms reach equilibrium for M
s
 - 4.Standard shock jump conditions for M
s
- 4 lead to post-shock temperatures in the corona in the range 107 to 1.8 × 107K and emission measures from 3.8 × 1047 to 3.8 × 1048 cm-3. For isolated simple events, I predict an exponential decay of the emission measure with decay times in the range 1   6.5 min.In a detailed study of over 4000 X-ray bursts, Drake (1970) compares 1 to 6 keV X-ray data with 7.7 to 12.5 keV X-ray data (the  thermal component) and finds ranges for the temperatures of 1.2 × 107 to 1.8 × 107K, for the emission measures of 5.1 × 1047 to 3.8 x 1048 cm-3 and for the decay times 0.5 20 min. He also finds that the emission measure varies  ... both from event to event and within the event, by more than a factor of two .The agreement between the predictions and the observations makes it appear that a strong shock in the corona will produce a post-shock state that yields the observed characteristics of the soft component of X-ray bursts (the thermal X-rays).I give several examples where sprays and fast eruptive prominences
, that are not associated with solar flares, are associated with thermal X-ray bursts. There were two slow eruptive prominences (M  1) in the sample, and neither of them yielded a detectable X-ray burst.Now at the Dept. of Physics and Astronomy (NASA), Univ. of New Mexico; Albuquerque, N.M. 87106. |
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