This pulsar has unique properties of radio emission, the most steep spectrum, the largest changes of pulse widths and phases and the presence of giant pulses.

We have used the VLA to image the location of the gamma-ray pulsar Geminga at 74 and 326 MHz. Upper limits to the pulse-averaged flux density, taking diffractive scintillation (DISS) into account, are S < 56 mJy (2σ; DISS quenched) at 74 MHz and S < 5 mJy (95% confidence) at 326 MHz. Intrinsic variability appears to be required in order to reconcile our upper limits with previous low-frequency detections.

Variable non-thermal radio emission from Galactic X-ray binaries is a trace of relativistic jets, created near accretion disks. The spectral characteristics of a lot of radio flares in the X-ray binaries with jets (RJXB) is discussed in this report. We carried out several long daily monitoring programs with the RATAN-600 radio telescope of the sources: SS433, Cyg X-3, LSI +61°303, GRS 1915+10 and some others.

Many flaring RJXB show, exponential and power laws of flare decay. Moreover, these different laws could be present in one or several flares and commonly flare decays are faster at a higher frequency. The decay law seems to change because of geometric form of the conical hollow jets. The synchrotron and inverse Compton losses could explain general frequency dependences in flare evolution.

Radiation mechanism for relativistc charged particles spiraling along curved magnetic field is considered. Emission from many electron revolutions around force line is taken into account.

The presence of a longitudinal magnetic field is shown to lead to the appearance of an additional component of the frequency spectrum of the linearly polarized emission. This component is proportional to the spectrum of normal waves phase difference fluctuations. The fluctuations spectra baseline dependence of a linear polarized radiation is periodical near zero frequency, one is absent in the high frequency ranges and such dependence has different character in magnetoactive plasma with electron density irregularities and in plasma with a random magnetic field.

This paper reviews planetary radio astronomy at low frequencies. At least at frequencies observable from the Earth's surface, this field has been almost solely the study of Jovian magnetospheric emissions. With the discovery of extra-solar planets, and the potential for new telescopes with large collecting areas, we may well see more objects and emission mechanisms becoming detectable.

This review is concerned to study of sun at frequencies lower than 1.4 GHz. Emphasis is made on results which illustrate the topics in which GMRT could play a major role. Coordinated studies including spectral and imaging radio observations are important for research in solar physics. Joint observations between the Giant Meter Radio Telescope (GMRT) with radio instruments located in the same longitude range are encouraged. This review inludes three distinct topics: Electron beams and radio observations- Radio signatures of Coronal Mass Ejections- Radio signatures of coronal and interplanetary shocks.

When radio waves propagate through a irregular medium, scattering by the random refractive index inhomogeneities can lead to a wide variety of phenomena, which include intensity scintillation. The observed scattering can be interpreted to gain information about the random medium and such inversion studies are valuable when the accessibility of the medium becomes difficult. This paper briefly describes the intensity scintillation of celestial radio sources caused by the turbulence in the solar wind and summarizes the salient features of the method employed in mapping the structure of disturbances leaving the Sun out to ∼1 AU.

The Miyun Synthesis Radio Telescope (MSRT), Beijing Astronomical Observatory, has been used in observation of the Sun as an one dimension heliograph. Daily observation with MSRT and other two single dishes for total power measurement have been performed since May,1998.(Zhang, X.Z., 1999)

This paper presents a detailed analysis of 80 type III radio bursts, two noise storms and 10 type II radio bursts observed in the 30-80 MHz range with the new radio spectrograph (Madurai Solar Radio Spectrograph) when it was operated on a daily basis during the periods December 1997 — April 1998 and August 1998. Results from statistical analysis of type III bursts are in agreement with earlier results. Employing a technique of separating the background continuum of noise storms show that the continuum is produced by electron accumulated from the preceding bursts. Also it is seen that the number of occurrences of type I bursts is maximum during the maximum of the background continuum. Comparison of records of type II bursts from MSRS with other spectrographs (Culgoora & Hiraiso) for the same bursts indicate that the sensitivity of the MSRS at low frequencies is much better than the other spectrographs.

In the framework of the plasma theory of solar radar echoes results of the known James' experiments such as the values of effective cross-sections, the anisotropy of reflections, the spectrum of reflected signals, the heights of radar scattering and others are explained. In particular in this theory reflection of radar signal with high effective cross-sections (σ = (10 − 100)πR2⊙) occur in processes t + l ⇌ t + l on the Langmuir turbulance generated by Type III electrons at altitudes (1.4—1.6)-R⊙ when electron streams propagate towards the Earth. If the electrons move away from the Earth then the scattering cross-sections due to process t + l ⇌ t + l are small (σ < πR2⊙). Reflections from the heights up to 5R⊙ can occur at scattering of radar wave on the ion-sound turbulance (processes t + s ⇌ t) accompanied the Langmuir turbulance.

The Giant Metrewave Radio Telescope (GMRT) is a major new facility available for observations at metre wavelengths. This paper describes the the GMRT with emphasis on the features that are of relevance to a potential user. The current state of the GMRT is also described.

The NRL and the NRAO have jointly implemented a low frequency capability on the Very Large Array. Operating at 73.8 MHz, this new frequency band offers unprecedented sensitivity (∼ 25mJy/beam) and resolution (∼ 25″). This paper briefly describes the this new receiving system, and the methodology for using it for astronomy.

Many lessons gained in imaging 74 and 330 MHz VLA data are of practical interest to future users of the GMRT and other low frequency observers. Three important issues are 1) radio frequency interference excision, 2) self-calibration, and 3) wide-field imaging. Recently developed tasks to address these and other problems encountered in low frequency VLA data reduction now exist or are being developed in both AIPS and AIPS++. We will describe how we use some of these new tools to routinely generate wide-field, low frequency images with sensitivities approaching thermal or classical confusion limits.

Over the past several years an international community of scientists and engineers has emerged with a common goal to solve the technical challenge required to construct a giant radio telescope with a collecting area of one square kilometre. The Square Kilometre Array (SKA) will have a hundred times more collecting area than our most powerful existing radio telescopes, providing sensitivity of a few tens of nanoJy in the centimetre/decimetre wavelength continuum. With a spatial resolution better than the Hubble Space Telescope, a field of view larger than the full moon, and the ability to simultaneously image a wide range of red shift, the SKA will be the worlds premier spectroscopic imaging telescope at any waveband.

At long wavelengths the SKA will be able to detect emission from atomic hydrogen gas at extreme redshifts, allowing study of the “Dark Ages” of the Universe, before, and during, the transition phase when the initial stars formed and reionization occurred. The combination of sensitivity, wide field of view and high angular resolution, will allow high resolution imaging of the interstellar media and magnetic field of a vast number of galaxies to high redshift. Measurements of atomic hydrogen emission and continuum emission will trace the star formation history of the Universe from primordial galaxies to the present.

We present the concepts and their unique features presently being studied for the Square Kilometer Array expected to be operational between 2010 and 2015. A comparison is made between telescopes in operation to day and SKA ambitious set of requirements is presented. The framework for coordinating the studies of various countries aiming to conclude on a concept choice in 5 years is introduced. As a desirable side effect, efforts relevant for SKA, will result in new albeit smaller telescopes coming into operation at earlier stages.

Decametric wavelength imaging has been largely neglected in the quest for higher angular resolution because ionospheric structure limited interferometric imaging to short (< 5 km) baselines. The long wavelength (LW, 2—20 m or 15—150 MHz) portion of the electromagnetic spectrum thus remains poorly explored. The NRL-NRAO 74 MHz Very Large Array has demonstrated that self-calibration techniques can remove ionospheric distortions over arbitrarily long baselines. This has inspired the Low Frequency Array (LOFAR)—-a fully electronic, broad-band (15—150 MHz)antenna array which will provide an improvement of 2—3 orders of magnitude in resolution and sensitivity over the state of the art.

The LOw Frequency ARray is a Digital Software Radio Telescope under study by the NFRA and the NRL. A scaleable architecture is proposed for the antenna stations of an aperture synthesis array operating in the 10 — 160 MHz frequency band. The use of advanced phased array technology with digital beamforming results in a multi-beam capability of up to 64 beams, which cover together about a steradian on the sky, and can be placed such that all relevant science objects are covered simultaneously. Based on the fast expansion of high performance processing technology, it is just after 2003 that signal and data processing will no longer dominate the cost of LOFAR in producing a confusion limited sky survey at the mJy level.

We present a preliminary study of A LOw Frequency Orbiting Telescope (ALOFT) which co-observes with ground radio telescopes, in a similar fashion to the current VSOP mission. Our current straw-man ALOFT mission has a spacecraft operating at three frequency bands (0.33, 0.6, and 1.4—1.6 GHz) in an orbit with a 10,000 km apogee height. It should be relatively low cost as the lower frequencies less stringently constrain the design, for example uncooled receivers, narrower bandwidth, and simple antennae. The major science goal to be addressed by this mission is to examine scattering phenomena through the technique of space VLBI, although other problems, such as AGN physics, can of course also be addressed.

The GMRT represents a dramatic improvement in ground-based observing capabilities for low frequency radio astronomy. At sufficiently low frequencies, however, no ground-based facility will be able to produce high resolution images while looking through the ionosphere. A space-based array will be needed to explore the objects and processes which dominate the sky at the lowest radio frequencies. An imaging radio interferometer based on a large number of small, inexpensive satellites would be able to track solar radio bursts associated with coronal mass ejections out to the distance of Earth, determine the frequency and duration of early epochs of nonthermal activity in galaxies, and provide unique information about the interstellar medium.