Evidence for a common origin of the electrons responsible for the impulsive X-ray and type III radio bursts

Abstract

Observations of impulsive solar flare X-rays > 10 keV made with the OGO-5 satellite are compared with ground based measurements of type III solar radio bursts in 10-580 MHz range. It is shown that the times of maxima of these two emissions, when detectable, agree within ~ 18 s. This maximum time difference is comparable to that between the maxima of the impulsive X-ray and impulsive microwave bursts. In view of the various observational uncertainties, it is argued that the observations are consistent with the impulsive X-ray, impulsive microwave, and type Ill radio bursts being essentially simultaneous. The observations are also consistent with 10--100 keV electron streams being responsible for the type III emission. It is estimated that the total number of electrons > 22 keV required to produce a type III burst is < 1034. The observations indicate that the non-thermal electron groups responsible for the impulsive X-ray, impulsive microwave, and type III radio bursts are accelerated simultaneously in essentially the same region of the solar atmosphere.The most characteristic non-thermal emissions during a solar flare are the impulsive hard X-ray, impulsive microwave, and type III radio bursts. In general the X-ray emission > 10 keV consists of two components, viz. impulsive and slow, the impulsive emission being the bremsstrahlung radiation from non-thermal electrons >~ 10 keV accelerated during the flash phase (Kane, 1969;Kane and Anderson, 1970). The type III radio emission, which is characterized by a fast frequency drift in time from high to low frequencies (Wild, 1950), is also an impulsive phenomenon usually associated with the flash phase (Malville, 1962). The characteristics of the type III radiation have been discussed by Wild et al. ), Maxwell (1965), Kundu (1965), Smith (1970a, and others. Following the initial suggestion by Wild et al. (1959) andby de Jager (1960), the type III radio bursts are generally believed to be excited by streams of energetic electrons moving outwards through the solar corona (Alvarez et al., 1972). De Jager (1960, 1962 noted that the kinetic energy of the electrons generating type III radio emission is similar to that of the electrons responsible for the hard X-ray emission. Moreover, the duration of a hard X-ray burst and a group of type III bursts at meter wavelengths is nearly the same. Therefore, he pointed out that a good correlation should exist between the hard X-ray and type III radio bursts. Winckler et al. (1961) and Anderson and Winckler (1962) indeed found a good correlation between the hard X-ray and type III radio bursts (two events). On the other hand, from a study of seven flares events, Kundu (1961) concluded that the correlation between these two types of emissions is weak. This led de Jager and Kundu (1963) to suggest that (i) hard X-rays and type III radio bursts are due to different jets of electrons accelerated (above the chromosphere) in different directions and (ii) simultaneous hard X-ray and Solar Physics 27 (1972) 174--181.

A Source of Energetic Particles Associated with Solar Flares

“…Observed electromagnetic emissions indicate that a source region often simultaneously produces ascending and descending energetic particles. The temporal correlation of the X-ray emitted from the chromosphere and the type III radio bursts emitted in the corona in a typical a Ñare event presents clear evidence (Kane 1972(Kane , 1981Aschwanden 1999a). Since only acceleration taking place in a magnetic Ðeld reconnection layer can produce simultaneously these ascending and descending energetic particles, it is compelling to suggest that reconnection is essential.…”

A tiny event producing an interplanetary type III burst

“…Very many flares, particularly impulsive flares (e.g., Cane & Reames 1988), exhibit type III bursts at their onset. Several publications are available about the statistical relationship between type III bursts and HXR bursts (e.g., Kane 1972Kane , 1981Hamilton et al 1990;Aschwanden et al 1995). More recently, Benz et al (2005Benz et al ( , 2007 studied a large number of flares above GOES class C5 and found that nearly all flares were associated with coherent radio emission between 4 GHz to 100 MHz; most of their flares with coherent radio emission had type III bursts.…”

On the Acceleration Processes in Solar Flares

“…However, it appears that the situation is not that simple. First of all, when we try to correlate type III bursts and microwave bursts, we find that an exact time coincidence can be proved in less than 25% of cases (Svestka and Fritzova, 1974;Kane, 1972). In some other cases the coincidence may still exist since there is a series of type III bursts which lasts during the period when the microwave burst occurs.…”