THE 1991 MARCH 22 FLARE - POSSIBLE ANISOTROPY OF HIGH-ENERGY NEUTRAL EMISSION

We made a parameter fit to the Haleakala neutron monitor counting rate during the 1991 March 22 solar flare (Pyle and Simpson, 1991) using t he time profiles of gamma-rays at 0.42-80 MeV obtained with the GRANAT satellite (Vilmer et al., 1994) and the microwave data from Owens Val ley Radio Observatory. We use a two-component neutron injection functi on to find that either an impulsive injection or the 'impulsive-plus-p rolonged' neutron injection is possible. In both cases, the number of > 300 MeV neutrons emitted towards the Earth is estimated as approxima te to 2 x 10(27) sr(-1), which is less than hat of the 1990 May 24 Rar e by an order of magnitude. We tested if such a big difference in neut ron number detected on the Earth can be accounted for solely by their different positions on the solar disk. For the estimation of the degre e of anisotropy of high-energy secondary emission, we made use of macr oscopic parameters of the flare active region, in particular, the vect or magnetogram data from the Big Bear Solar Observatory. In our result , the anisotropy factor for the neutral emissions of the 1991 March 22 Rare is only approximate to 1-10, which is rather small compared with previous theoretical predictions for a disk flare. Such a moderate an isotropy is due to the relatively large inclination angles of the magn etic fields at the footpoints of the flaring loop where accelerated pa rticles are trapped. We thus concluded that the smaller number of neut rons of the 1991 March 22 flare would be not only due to its location on the disk, but also due to fewer protons accelerated during this eve nt as compared with the 1990 May 24 limb event. For a more precise det ermination of the anisotropy factor in a flare, we need a detailed spe ctrum of electron bremsstrahlung in 0.1-10 MeV and the fluence of gamm a-ray emission from the pi(0)-decay.