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Simultaneous ultraviolet and X-ray observations of solar microflares
Porter, J. G.; Fontenla, J. M.; Simnett, G. M.
AA(NASA. Marshall Space Flight Center, Huntsville, AL), AB(NASA. Marshall Space Flight Center, Huntsville, AL), AC(NASA. Marshall Space Flight Center, Huntsville, AL)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 438, no. 1, p. 472-479 (ApJ Homepage)
Publication Date:
Solar Physics
NASA/STI Keywords:
Solar Flares, Solar Magnetic Field, Solar X-Rays, Ultraviolet Radiation, Polarimeters, Solar Corona, Solar Maximum Mission, Ultraviolet Spectrometers
Bibliographic Code:


We present a comparison of observations of a solar active region obtained with the Ultraviolet Spectrometer and Polarimeter (UVSP) and the Hard X-ray Imaging Spectrometer (HXIS) on board the Solar Maximum Mission (SMM). The data show many subflares and smaller events during a 9 hr period in which there were no major flares. This activity is associated with areas of complex, evolving magnetic fields. Events substantially smaller than subflares, identified in C IV 1548 A emission (T = 105 K), are found to have impulsive counterparts in 3.5-5.5 keV X-ray emission characteristic of T approximately 107 K. These 'microflares' are therefore true members of the flare family, reaching temperatures greater than that of the ambient solar corona. Plots of X-ray versus UV emission show that the emission from the smaller microflares is softer than that from the larger microflares and subflares. Distributions of solar flares with energy that are based on hard X-ray fluxes can be corrected using this X-ray/UV relationship. The corrected distributions suggest that microflares play a larger role in coronal heating than was indicated by analysis of the original distributions.

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