Solar Plasma Density and Spectrum of Accelerated Particles Derived From the 2.223-Mev Line of a Solar Flare

Abstract

The time profile of the neutron capture line of 2.223 MeV for the flare of 16 December 1988 (its third peak) is analyzed. The enhancements of plasma density in the deep photospheric layers of the Sun under the flare region (an effect of density enhancement) have been deduced by the SINP calculation code. These enhancements are studied based on several modified models of the lower chromosphere, photosphere, and convection zone. Additionally, the case has been examined when the neutron source is placed at the top of the photosphere. The energy spectrum of accelerated particles (protons) is shown to evolve with time. Assuming a stochastic mechanism of acceleration and a Bessel function for the spectrum, we find the spectral index αT to increase from 0.005 to 0.1 during the decay phase of the burst; i.e., the proton spectrum becomes harder. Density enhancements found in the flare of 16 December 1988 are consistent with our previous results on the density enhancement effects deduced for two other flares, 6 November 1997 and 22 March 1991. It is suggested that density enhancements in the deep layers of the photosphere may be rather common features of powerful solar flares. B.M. Kuzhevskij is deseased. E.V. Troitskaia ( ) · B.M. Kuzhevskij

Solar Cosmic Rays

“…Subsequent analysis of a set of other flares (6 November 1997, 16 December 1988, and 28 October 2003 confirmed an effect of plasma density enhancement (EDE) at the photospheric and sub-photospheric levels during those four flares mentioned (e.g., Kuzhevskij et al 2005a). Some later it was shown that the 2.223 MeV line data may be used to link the line fluences with a form of the spectrum of accelerated protons in the source (Kuzhevskij et al 2005a;Troitskaia et al 2007Troitskaia et al , 2009). Below we consider this possibility in more details.…”

“…From this simple expression one may conclude that the observed intensity-time profile of gamma-emission of 2.223 MeV contain also the information on the neutron spectrum and plasma density in the region of neutron energy loss. Based on those findings, the authors have developed original approach and elaborated special method (SINP code) to determine the most probable profile of plasma density in the photosphere and adjoining levels during the period of a flare (for details see Kuzhevskij et al 1998Kuzhevskij et al , 2005aTroitskaia et al 2007).…”

“…With several plausible models of the solar atmosphere density, this code was successfully applied to a number of large gamma-ray flares: 16 December 1988, 22 March 1991, 6 November 1997, and 28 October 2003(Gan et al 2003Kuzhevskij et al 2005a;Troitskaia et al 2007Troitskaia et al , 2009. As a result, the authors have obtained some evidence of the effect of density enhancement (EDE) in the sub-flare region.…”

The results of January 20, 2005 solar flare study by narrow gamma lines

“…Model 5 is a specially selected form best describes the vertical profile of the density of the solar atmosphere during flares and is combined of dashed part and two parts of model 1. Modeling technique of such flares, for example, was developed in [8,9,12,13]. Now we apply our method to the flare under consideration.…”