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The RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) website lists solar Hard X ray flares with energy of each flare given in a range, say, 50 - 75 keV. We presume that is the energy observed by the satellite (like GOES satellite) or ground based instrument, so that accounting for the sun-earth distance, one can estimate the total energy of flare over its total duration. That could be of the order of 10^27 - 10^32 ergs. Hence, my question is how we can convert the given, say, 75 keV energy value in the RHESSI flare list into total energy in ergs.?

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  • $\begingroup$ Generally instruments like those on RHESSI measure a flux or energy flux of particles, in this case photons. By knowing properties and the response function of the instrument, one can convert the flux to a total integrated energy density, energy, or power, etc. (whatever units you want). So you measure the flux versus time, integrate over time, solid angle, area, and particle energy to get the total energy released by a flare (overly simplified, but it's close enough to get the point across). $\endgroup$ – honeste_vivere Apr 1 '15 at 13:24
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I am afraid, that the number 50-75 keV concerns one single (Xray) photon, not the whole flare. Maximum you can get from these two numbers is estimation, how many photons participated on the flare. One photon energy 50 keV = $8\times 10^{-15} J = 8 \times 10^{-8} ergs$.

Your answer concerning the total energy is actually those $10^{27}-10^{32}$ ergs.

Remark: you probably cannot detect these Xray flares by ground instruments, as Xray is attenuated in atmosphere.

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