The solar white-light flare of 1989 March 7 - Simultaneous multiwavelength observations at high time resolution

Abstract

Abstract : We present observational data for the 1989 March 7 white-light flare (WLF), including SMM/HXRBS hard X-ray measurements and CCD optical images in 5000 A continuum and at 3 A in the red and blue wings of the H alpha line. The optical data were acquired at a 0.5 s rate under good seeing and were further processed to remove image motion and distortion. The flare kernel shows an impulsive rise in both H alpha and continuum that is well correlated with impulsive hard X-rays. The Hot emission shows a red asymmetry which we interpret as Doppler redshift associated with explosive heating of the chromosphere. These results are consistent with previous observational descriptions which traditionally have been interpreted in terms of heating and ionization of the flare chromosphere by a nonthermal electron beam. However, new observational results which have not been reported previously include (1) the separation of the flare kernel into a bright inner core and a fainter outer region, where the two components display distinctly different temporal behavior and amount of Hot red asymmetry, and (2) a delay, relative to hard X-rays, of approx. 1 s in the impulsive rise of the H alpha wing emission, followed by an additional 1-2 s delay in the 5000 continuum. It is concluded that the observed fluxes and timing of the hard X-ray and WLF optical emissions are consistent with chromospheric heating by nonthermal electrons, with additional visible light continuum possibly being contributed by a backwarmed photosphere irradiated by intense chromospheric recombination continua (principally Balmer continuum) .... Sun: flares, Sun: X-rays, Gamma rays.