Bursts Of Radio Emission Research Articles

Non-relativistic solar electrons

This review summarizes both the direct spacecraft observations of non-relativistic solar electrons, and observations of the X-ray and radio emission generated by these particles at the Sun and in the interplanetary medium. These observations bear on three physical processes basic to energetic particle phenomena: (1) the acceleration of particles in tenuous plasmas; (2) the propagation of energetic charged particles in a disordered magnetic field, and (3) the interaction of energetic charged particles with tenuous plasmas to produce electromagnetic radiation. Because these electrons are frequently accelerated and emitted by the Sun, mostly in small and relatively simple flares, it is possible to define a detailed physical picture of these processes. In many small solar flares non-relativistic electrons accelerated during flash phase constitute the bulk of the total flare energy. Thus the basic flare mechanism in these flares essentially converts the available flare energy into fast electrons. Non-relativistic electrons exhibit a wide variety of propagation modes in the interplanetary medium, ranging from diffusive to essentially scatter-free. This variability in the propagation may be explained in terms of the distribution of interplanetary magnetic field fluctuations. Type III solar radio burst emission is generated by these electrons as they travel out to 1 AU and beyond. Recent in situ observations of these electrons at 1 AU, accompanied by simultaneous observations of the low frequency radio emission generated by them at 1 AU provide quantitative information on the plasma processes involved in the generation of type III bursts.

SIMULTANEOUS OPTICAL AND RADIO OBSERVATIONS OF THE FLARE STAR EV LACERTAE

ABSTRACT Simultaneous optical and radio observations of the flare star EV Lac have been carried out. The only optical flare detected was followed by a burst of radio emission which lagged about 4 minutes behind the optical event. Key words: flare stars

Search for sporadic radio-emission from cosmic space at centimeter and decimeter wavelengths

The uniformity of the properties of the radio-emission bursts over a large territory and the dependence of their characteristics on manifestations of solar activity lead to the following conclusions.

A Search for Isolated Radio Pulses from the Crab Nebula at 151.5 MHz

A search has been made for large bursts of radio emission at 151.5 MHz from the direction of the Crab Nebula. In 605 hr of observation, no events exceeding a flux of 1.4 × 10 −22 W m −2 Hz −1 were detected. This therefore sets an upper limit for the energy in radio pulses from the direction of the Crab Nebula which might be associated with the events recorded in the gravitational wave experiments of Weber. Implications of the results with regard to ‘strong pulses’ and phase fluctuations in the periodic emissions from the pulsar NP 0532 are also examined.

Evidence for electron excitation of type III radio burst emission

Type III radio bursts observed at kilometric wavelengths (≲ 0.35 MHz) by the OGO-5 spacecraft are compared with > 45 keV solar electron events observed near 1 AU by the IMP-5 and Explorer 35 spacecraft for the period March 1968–November 1969. Fifty-six distinct type III bursts extending to ≲ 0.35 MHz (≳ 50 R ⊙ equivalent height above the photosphere) were observed above the threshold of the OGO-5 detector; all but two were associated with solar flares. Twenty-six of the bursts were followed ≲ 40 min later by > 45 keV solar electron events observed at 1 AU. All of these 26 bursts were identified with flares located west of W 09 solar longitude. Of the bursts not associated with electron events only three were identified with flares west of W 09, 18 were located east of W 09 and 7 occurred during times when electron events would be obscured by high background particle fluxes. Thus almost all type III bursts from the western half of the solar disk observed by OGO-5 above a detection flux density threshold of the order of 10−13 Wm−2 Hz−1 at 0.35 MHz are followed by > 45 keV electrons at 1 AU with a maximum flux of ≳ 10 cm−2 s−1 ster−1. If particle propagation effects are taken into account it is possible to account for lack of electron events with the type III bursts from flares east of the central meridian. We conclude that streams of ≈ 10–100 keV electrons are the exciting agent for type III bursts and that these same electrons escape into the interplanetary medium where they are observed at 1 AU. The total number of > 45 keV electrons emitted in association with a strong kilometer wavelength type III burst is estimated to be ⩾ 5 × 1032.

Radio Observations of Flare Stars

Observations of the radio emission from the red dwarf flare stars in the solar neighbourhood have been made at Jodrell Bank since 1958. In Australia, observations have been made both of these flare stars and of the early type flare stars in stellar aggregates. Observations in both Britain and Australia have been hampered by the difficulties involved in obtaining radio and optical coverage at the same time.In the initial Jodrell Bank programme, at a frequency of 240 mhz, between 1958 and 1960, 474 hours of observations were obtained, mostly on UV Ceti, and 13 events compatible with bursts of radio emission from the star were seen, but due to poor seeing conditions at the Cambridge Observatories the correlation between radio and optical flares could not be established, although the rate of occurence of radio events was similar to the reported rate for optical events of a few magnitudes.

Decameter radio emission from Jupiter and solar activity

It is found that there is an apparent increase in solar activity prior to the emission of decametric radio bursts from Jupiter during years of high solar activity. It is pointed out that Jupiter data contains artificial periodicities due to the observational procedures. The observed correlations between Jupiter radio bursts and solar activity can be explained as being due to the presence of these artificial periodicities in Jupiter data.

Correlations of solar-flare electron events with radio and X-ray emission from the sun

The > 40-keV solar-flare electrons observed by the IMP III and Mariner IV satellites are shown to be closely correlated with solar radio and X-ray burst emission. In particular, intense type III radio bursts are observed to accompany solar electron-event flares. The energies of the electrons, the total number of electrons, and the size of the electron source at the sun can be inferred from radio observations. The characteristics of the electrons observed in interplanetary space are consistent with these radio observations. Therefore these electrons are identified as the exciting agents of the type III emission. It has been noted that the radio and X-ray bursts are part of the flash phase of flares. The observations indicate that a striking feature of the flash phase is the production of electrons of 10–100 keV energies.

Some aspects of type II bursts

The outstanding bursts of radio emission from the sun, which are termed spectral type II or “slow-drift” bursts, are a rare phenomenon. Even at sunspot maximum the average rate of occurrence is only about one burst every 50 hours, so that a long series of observations is needed to define the characteristics of the bursts. The present study uses the records made over the past 5½ years with the 40 to 240 Mc/s Dapto radio spectrograph. During this period, 65 bursts of this type were recorded.

Bursts of Radio Emission

Bursts of Radio Emission

Solar Radio Asymmetry at 4-Metres Wave-length

IN 1948, Hey, Parsons and Phillips1 reported that at 4.1-metres wave-length bursts of radio emission, usually of a few minutes duration, occurred more often in association with flares on the eastern half of the sun's disk than on the western half. Subsequent observations have confirmed this conclusion. In a recent analysis of radio emissions at 1.5-metres wavelength, Dodson, Hedeman and Owren2 could find no evidence of this asymmetry. The following reasons may explain why they failed to observe the effect.