The Distribution of Flare Parameters and Coronal Heating
Abstract
The differential distributions of solar hard X-ray peak count rates and peak flux densities together follow a power law over more than four orders of magnitude in peak count rate or peak flux density and extend to the limit of sensitivity of the instruments (Dennis 1985, Solar Phys., 16, 152.; Lin et al., 1984, Ap. J., 283, 421). This behavior has led some to speculate that the greater number of smaller events could be energetically important in coronal heating (Lin et al., 1984, Ap. J., 283, 421). Assuming the hard X-rays are bremsstrahlung from a distribution of accelerated electrons impinging on a thick target, we determine the relationship between the total flare energy released in the corona and observable flare parameters. We find that for smaller flares to be energetically more important, there must be an anticorrelation between fluence and the photon spectral index, the ratio of energy that goes directly into heating to the energy that goes into acceleration of electrons, the inverse of the low energy cutoff of the spectrum, or any combination of these. There is little or no observational evidence which has direct bearing on the low energy cutoff, but anticorrelations with the other parameters can in principle be tested. We have searched for an anticorrelation between fluence and spectral index using ISEE-3/ICE solar hard X-ray data. Using a new statistical test which properly takes account of the effects of data truncation due to selection effects (Ephron and Petrosian, 1992, to be published in Ap. J.), we find no anticorrelation, thus no evidence that smaller flares are energetically more important. To test the second anticorrelation we have examined the distribution of soft X-ray emissions using the GOES database. We find that the distribution of GOES peak fluxes is steeper than the distribution of hard X-ray fluences, contrary to what would be expected if the Neupert effect were evident in most flares. We will present a discussion of the implications of this discrepancy for coronal heating. This work was supported by NASA Grant NAGN 1976 and NSF Grant ATM 90-11628.
- Publication:
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American Astronomical Society Meeting Abstracts #180
- Pub Date:
- May 1992
- Bibcode:
- 1992AAS...180.4102L