The low-frequency radio spectrum of the continuum emission from the undisturbed sun

The low-frequency radio spectrum of the continuum emission from the undisturbed Sun is determined for 24 days during the period 1985 May-September. It is found that the spectral index varied from + 1.6 to +3.6 during this period. It is suggested that the large positive spectral indices are due to the existence of temperature gradients in the outer corona.     

Observations and analysis of lunar radio emission at 3.09 mm wavelength

Earth, Moon, and Planets - Observations of lunar radio emission were made at 3.09 mm wavelength (97.1 GHz) from April 18 to May 20, 1971. Absolute brightness temperatures were measured for five...     

Decimeter continuum radio emission from a post-flare loop

Radio observations offer an important means for providing estimates of magnetic fields in post-flare loops.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985.     

Solar radio emission at 1.2 mm wavelength

Some properties of solar active regions at 1.2 mm wavelength are discussed. Equatorial and polar brightness distributions of the quiet Sun at 1.2 mm wavelength are also presented.     

A self-consistent model for the storm radio emission from the Sun

A self-consistent theoretical model for storm continuum and bursts is presented. We propose that the Langmuir waves are emitted spontaneously by an anisotropic loss-cone distribution of electrons trapped in the magnetic field above active regions. These high-frequency electrostatic waves are assumed to coalesce with lower-hybrid waves excited either by the trapped protons or by weak shocks, making the observed brightness temperature equal to the effective temperature of the Langmuir waves.It is shown that whenever the collisional damping ( _c ) is more than the negative damping (- _A ) due to the anisotropic distribution, there is a steady emission of Langmuir waves responsible for the storm continuum. The type I bursts are generated randomly whenever the collisional damping ( _c ) is balanced by the negative damping (- _A ) at the threshold density of the trapped particles, since it causes the effective temperature of Langmuir waves to rise steeply. The number density of the particles responsible for the storm radiation is estimated. The randomness of type I bursts, brightness temperature, bandwidth and transition from type I to type III storm are self-consistently explained.On leave from Indian Institute of Astrophysics, Bangalore 560034, India.     

Spotless flares and the associated radio continuum emission

We studied 24 spotless flares of Ha importance 1 which occurred during the 21st cycle of solar activity. The spotless flares could be grouped in three categories according to their location and time history of the associated active region. Our association of the flares with radio events was based on relative timing and on the flare importances. Weak microwave gradual rise and fall events were frequently recorded during the occurrence of the spotless flares. A few flares from our sample could be associated with impulsive and complex microwave bursts. Only in one case an association of a spotless flare with a significant metric type II/IV event seems to be justified.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.     

On the long-term behaviour of the circular polarization from coronal condensation radio emission at 4.3 cm wavelength

The circular polarization from coronal condensations at = 4.3 cm correspond to the extraordinary mode of propagation, due to the contribution of preceding spots' polarities, being usually left-handed. The fewer cases of right-handed polarization are normally associated to an excess of sunspot plages in the southern hemisphere, thus making it difficult to give evidence for magnetoionic coupling phenomena as a general rule.     

Observations of radio emission from the cosmic gamma-ray burst GRB 030329

We present the radio observations of the afterglow from the intense cosmic gamma-ray burst GRB 030329 performed with the radio telescopes of the Institute of Applied Astronomy, Russian Academy of Sciences, at the Svetloe (λ=3.5 cm) and Zelenchuk (λ=6 cm) Observatories. The difference between the fluxes measured in two different polarization modes suggests the existence of a circular polarization in the radio afterglow from GRB 030329. However, since the measurement errors of the fluxes with different circular polarizations are large, we cannot draw a firm conclusion about its detection; we can only set an upper limit on its value. An analysis of the possible generation mechanisms for the circular polarization of the relativistic jet suggests that there is a helical magnetic field in the jet. The existence of significant flux densities at various wavelengths during a long (≥10 days) period leads us to conclude that the hydrodynamic evolution of the relativistic bow shock takes place in the stellar wind, not in the interstellar medium. We have estimated the total GRB energy (E=10⁵¹ erg) (under the assumption of isotropic radiation) and the plasma density of the stellar wind from the presupernova (n=3 cm^?3). The magnetic-field strength in the relativistic jet can be estimated as B≈100 G.     

Radio emission from the Sun at 843 MHz

The Molonglo Observatory Synthesis Telescope (MOST) has recently been modified to permit observations of the Sun. With a collecting area of 18000 m², MOST makes high-sensitivity measurements in right-hand circular polarisation over a 3 MHz bandwidth at 843 MHz. The maximum baseline of the multi-element interferometer is 1600 m, so that one-dimensional spatial resolution as fine as 32 arc sec is available. A resistor array produces simultaneously a set of 64 beams separated by 22 arc sec, which may be offset electronically to cover the entire Sun in a few seconds. Observations may be made with a beam shape corresponding to either a multiplying or an adding interferometer. By exploiting the technique of Earth-rotation synthesis the telescope may be used to make two-dimensional maps of the Sun at the time of the austral solstice with a synthesized beamwidth of 43 × 110 arc sec. This paper describes the instrument and the procedures used to make various types of solar observations, and exhibits some of the first data collected.     

Pulsating radio emission at decametre wavelengths from the sun

Observations on the pulsation pattern in the time profile of short duration solar radio bursts at decametre wavelengths are presented. The pulsations are found to be present predominantly in the saturation phase of the burst. A tentative physical model based on the non-linear development of the waves interacting in a turbulent medium is invoked to explain the origin of the pulsations.     

Observations of Saturn at a wavelength of 49.5 cm

Radio emission from the planet Saturn was detected and measured by an unusually efficient observing technique at a wavelength of 49.5cm. The corresponding equivalent disk brightness temperature was hence determined to be 390 ± 65°K, providing further evidence for a mild enhancement in the emission at long wavelengths. It is pointed out that the currently available measurements of the disk brightness temperature in the wavelength range 1mm-1m are, as a whole, inadequate for estimating with confidence the detailed shape of the spectrum and that the exiguous, long wavelength observations should be supplemented with more and accurate measurements.     

Fine structure of the Sun at 1.3 cm wavelength

The two-element interferometer at Hat Creek Observatory was used at 1.3 cm wavelength to study the fine structure of the radio emissive regions on the Sun. Observations of the quiet Sun at 1.3 cm show sudden changes in the fringe amplitude and phase, lasting for typically about 5–8 min. Assuming that these events are identical in nature, a plot of peak amplitude vs the projected baseline at the time of the event suggests emission from a region of angular size of about 10″. The corresponding brightness temperature is 50000 K. It is possible that these events may be related to the appearance and disappearance of groups of spicules or mottles.     

Height of the slowly varying component of radio emission at 9.1 cm during the Quiet Sun Years

The slowly varying component of solar microwave emission is associated with plage and sunspot regions seen optically. Under the assumption that the microwave emission originates radially above the associated optical feature the height of the microwave emission region above the photosphere can be calculated.For 99 regions seen at 9.1 cm during the International Quiet Sun Years 1964–1965 the average height was 8000 km. This result compares with 18000 km measured for the same wavelength emission during 1960. A change of height in this direction could be the result of the changing strength of the magnetic field associated with regions seen during the two periods.     

Observations and interpretation of the slowly varying component of solar radio emission at decameter wavelengths

We have observed the slowly varying component of solar radio emission at a frequency of 34.5 MHz with half power beam widths of 26/40 in the east-west and north-south directions, respectively. It is found that the observed brightness temperatures vary within the limits of 0.3×10⁶K to 1.5×10⁶K, and the average half power widths of the brightness distribution on the Sun is about 3R . Thermal emission from coronal regions of various electron densities and temperatures with and without the magnetic field has been computed and compared with the observed results.     

Observations of prominences at 3.5 millimeter wavelength

At 3.5 mm wavelength absorption features are observed in correspondence with H dark filaments on the disk; beyond the limb the prominences correspond to emissive regions. The absorption features are larger (2–3 arc) than the corresponding H dark filaments; the emissive regions at the limb have similar angular sizes. The emissive regions at the limb have electron temperatures of 5500±500 K; the amount of absorption observed on the disk leads to mean electron densities of about 5 × 10¹⁰ per cm³.