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Comprehensive Multi­Wavelength Observations of
the 1992 January 7 Solar Flare
A.V.R. Silva, S.M. White, Robert P. Lin, I. de Pater, D.E.
Gary, J.M. McTiernan, H.S. Hudson, J.G. Doyle, M.J.
Hagyard and M.R. Kundu
Observations of a solar flare which occured at 2022 UT on 1992 January 7, dur­
ing the December 91/January 92 Max'91 Campaign, are presented here. This
flare was observed simultaneously in H alpha, ratio (at microwave and millime­
ter wavelenghts), and soft and hard X­rays (by the Yohkoh spacecraft) with
high spatial and moderate spectral resolution. A comparison of magnetograms
before and after the flare shows evidence of the emergence of new magnetic flux
of opposite polarity at the flare site. Although this flare was only of moderate
size (GOES classification C8.9 and H alpha importance SF) it exhibited several
distinct bursts and at least tem spatially distinct hard/soft X--ray sources. Co­
spatial H alpha brightenings suggest that most of the X­ray sources are located
at footpoints of magnetic loops. Two of the hard X­ray sources have no H alpha
counterpart and are thus believed to be located at loop tops. The flare consisted
of three bursts of particle acceleration followed by a purely thermal phase. High
spectral resolution Ca XIX line profiles indicate up­flows shortly after the second
acceleration phase. Analysis of the microwave/hard X­ray/soft X­ray emission
from individual sources provides information on the radio emission mechanisms,
the energetic electron population, the magnetic field strenght, and plasma den­
sity. These parameters were estimated for the two microwave sources observed
during the third acceleration burst, these sources were simultaneously detected
in soft X­rays and one of the sources is also seen in hard X­ray maps. Although
the microwave emission is consistent with the gyrosynchrotron mechanism, the
millimeter emission, which peaks during the thermal phase when all nonther­
mal activity has ceased, is likely due to thermal bremsstrahkung from the hot
soft X­ray emitting plasma. The energy lost to collisions by the energetic (!
15 keV) electrons and the energy contained in the thermal plasma are calcu­
lated for each source. The energy injected by the nonthermal electrons from all
sources is estimated to be 10 ( 30) erg. Only the soft X­ray sources with gradual
time profiles seem to show the Neupert effect.
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