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A Very Narrow RHESSI X-ray Flare on 25 September 2011 View all abstracts by submitter

Brian Dennis   Submitted: 2019-10-30 09:15

The unusually narrow X-ray source imaged with RHESSI during an impulsive spike lasting for ~10 s during the GOES C7.9 flare on 25 September 2011 (SOL2011-09-25T03:32) was only ~2~arcsec wide and ~10~arcsec long. Comparison with HMI magnetograms and AIA images at 1700 Å shows that the X-ray emission was primarily from a long ribbon in the region of positive polarity with little if any emission from the negative polarity ribbon. However, a thermal plasma source density of ~1012}~cm^{-3 estimated from the RHESSI-derived emission measure and source area showed that this could best be interpreted as a coronal hard X-ray source in which the accelerated electrons with energies less than ~50 keV were stopped by Coulomb collisions in the corona, thus explaining the lack of the more usual bright X-ray footpoints. Analysis of RHESSI spectra shows greater consistency with a multi-temperature distribution and a low energy cutoff to the accelerated electron spectrum of 22 keV compared to 12 keV if a single temperature distribution is assumed. This leads to a change in the lower limit on the total energy in electrons by an order of magnitude given the steepness of the best-fit electron spectrum with a power-law index of ~6.

Authors: Brian R. Dennis, Anne K. Tolbert

Publication Status: Accepted for publication in the Astrophysical Journal
Last Modified: 2019-10-30 13:06
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