The solar flare of 1980 March 29 at 0918 UT as observed with the hard X-ray burst spectrometer on the Solar Maximum Mission

Abstract

High-energy X-ray observations in the energy range from 26 to 386 keV are reported for the solar flare on 1980 March 29 starting at 09/sup h/17/sup m/10/sup s/UT. With the 1--2 s time resolution previously available, this flare would have appeared as the largest single hard X-ray spike ever reported with e-folding rise and fall times of approx.2 s, a FWHM of approx.10 s, and a peak flux of 6 photons cm/sup -2/ s/sup -1/ keV/sup -1/ at 50 keV. With the 10 ms time resolution available from the Hard X-Ray Burst Spectrometer on SMM, significant deviations from a smooth time profile can be resolved on the leading edge and at the peak of the burst. These deviations are in the form of at least five steps or eight separate peaks approx.1 s wide with separation times of 1--2 s. They are interpreted as resulting from multiple driven tearing-mode instabilities in a single magnetic loop or by a cascade effect in an arcade of loops. The photon-number spectrum on the leading edge and at the peak of the burst can be represented by a thermal bremsstrahlung function with the temperature and emission measure increasing to maximum values of approx.5 xmore » 10/sup 8/ K and approx.5 x 10/sup 45/ cm/sup -3/, respectively, at the time of peak intensity. On the trailing edge of the burst, the data show a significant excess at high energies (>100 keV) above the fitted thermal bremsstrahlung function. Such a high-energy tail may be the result of second-stage acceleration, or it may reflect the evolution of a single thermal electron distribution in some form of magnetic trap.« less