We describe the most complete, publicly accessible database of radio sources, CATS (“astrophysical CATalogues Support system”). It contains more than 300 catalogues of objects detected in various (mostly radio) wavelength ranges. Apart from catalogues drawn from the most important existing surveys and compilations (e.g. NVSS, FIRST, GB6, IRAS, ROSAT, PGC, MCG), CATS includes the largest low-frequency catalogues published so far: UTR, Culgoora, Cambridge, Miyun, WENSS, TXS, Bologna and Molonglo etc., CATS allows one to operate with these, and to draw samples of objects for the study of a large variety of astrophysical problems. Some modes of access are described here.

The project of the informational system creation on the problem of evolution of radio galaxies is described. This system, being developed at present, will allow a user to operate with simulated curves of spectral energy distributions (SED) and to estimate ages and redshifts by photometrical data. Planned modes of access, formats of output result and additional functions are described.

Until recently, high angular resolution and high sensitivity surveys of the radio emission from the plane of our Galaxy were available only at frequencies of several GHz, where large single dish radio telescopes provide arcminute scale angular resolution. At these frequencies thermal radiation from HII regions and diffuse ionized gas comprise a major component of the Galactic emission. Advances in wide field interferometric imaging techniques now make it possible to carry out high sensitivity surveys of the Galaxy with arcminute scale angular resolution at 1.4 GHz and below. Over the past few years initial synthesis surveys have been made. More ambitious surveys that combined sensitive continuum observations with full polarimetry and images of the 3-dimensional structure of atomic hydrogen gas at pc scales are currently underway in the northern (DRAO) and southern (ATNF) hemispheres. The interstellar medium of the Galaxy contains structure on all spatial scales, and these surveys combined data from aperture synthesis telescopes and signal dish antennas to provide full spatial frequency coverage to the resolution limit. Preliminary results reveal wide-spread features and processes in the the interstellar medium that are not readily visible by other means, including, for example, unusual atomic hydrogen structures related to the vertical transfer of matter and radiation between the disk and halo of the Galaxy, Faraday rotation structures that allow study of the magnetic field and diffuse ionized component in the plane of the Galaxy, and a cold atomic phase of the neutral medium that may provide a link between global shock phenomena in the galaxy and the formation of molecular clouds.

A survey of the southern Galactic Plane is being made in the radio continuum at 843 MHz with the Molonglo Observatory Synthesis Telescope. The area to be covered is 240° ≤ l ≤ 365°, |b| ≤ 10° with a resolution of 43″ × 43″cosec|δ| and a 3σ rms noise of ≤ 5 mJy/beam. This survey (MGPS2) will be used to search for possible new supernova remnant candidates, to image other discrete sources such as HII regions and radio galaxies located behind the Galaxy, and to study the structure of the interstellar medium. Comparison with a first epoch survey (MGPS1) will also be made. Some of the first results from MGPS2 are presented.

Radio sky surveys give us basic information about the origin of the radio emission from the Galaxy. By mapping the sky at several radio frequencies a separation of the thermal and non-thermal emission components is possible. The major part of the low-frequency radio emission comes from the synchrotron process, the braking of relativistic electrons in magnetic fields. By mapping the linear polarization at several frequencies (required for the correction of the Faraday rotation) the orientation of the magnetic fields in the emitting regions can be deduced. Older all-sky surveys at 30, 150 and 408 MHz have now been supplemented by new observations of the Galaxy at 45 and 1420 MHz. These surveys, in addition to being important as tracers of the morphology of the magnetic fields in the Galaxy, are also required to correct for the ‘foreground’ features in cosmological studies of the COBE data and the PLANCK surveys in the future. Studies of the Galaxy in polarization have been made some years ago indicating high percentage of linear polarization in various directions. More recent work with good angular resolution has shown spectacular polarized intensity structures in selected regions. Low-frequency data with good angular resolution are urgently required for the interpretation of these features.

Observations of nearby galaxies in radio continuum (both total power and polarized intensity) have given us the possibility to study magnetic fields in objects at known distances. Polarization observations of nearby galaxies have confirmed the existence of regular magnetic fields in practically every object so far studied. Originally data were obtained from large single-dish telescopes, notably from Effelsberg and Parkes. These data were greatly enhanced by the addition of higher resolution components from the VLA and ATCA respectively. These results indicate surprisingly homogeneous magnetic fields in most galaxies. High angular resolution observations with the GMRT at lower radio frequencies will add a new dimension to the data on galaxies.

Figure 1 presents a wide-field, high dynamic-range, 327 MHz VLA2 image of the Galactic center (GC). This image was constructed from archival VLA data using new 3-D image restoration techniques which resolve the problem of non-coplanar baselines encountered at long wavelengths. In a recent paper (LaRosa et al. 2000) we presented a catalog of over a hundred sources from this image, 23 extended sources and 78 small-diameter sources. The catalog contains flux densities, positions, sizes, and, where possible, a 20/90 cm spectral index. We also present subimages of all the extended sources. We refer the reader to LaRosa et al. (2000) for the details. In this note we will concentrate on observations of the nonthermal filaments and briefly describe a new model for their formation.

The origin and evolution of the nonthermal filaments (NTFs) observed in the GC is an outstanding problem. All of the 7 classified NTFs are visible on Figure 1: Four of these are labeled threads, the other three are the “Snake,” the “Pelican,” and the Sgr C filament. The wide-field imaging at 327 MHz lead to the discovery of the “Pelican” (Lang et al. 1999). This filament has the distinction of being the farthest NTF in projection from Sgr A and the only NTF that is parallel to the Galactic plane. One critical issue for understanding the activity and overall structure of the GC is whether these filamentary sources trace a pervasive, large-scale magnetic field or are local independent structures (e.g., Yusef-Zadeh 1989; Morris 1994, 1996; Uchida & Gusten 1995; Yusef-Zadeh, Wardle & Parastaran 1997; Shore & LaRosa 1999; Lang et al. 1999; Lang, Morris & Echevarria 1999; LaRosa et al. 2000).

We present a preliminary image of the Galactic Centre region at 74 MHz made using the Very Large Array (VLA)

We have started a project to study the Galactic Centre region using the GMRT in all it's frequency bands. For the first time, Galactic Centre have been imaged with high resolution at 610 MHz. Also, at 325 MHz, we have observed a few of the suspected supernovae remnants (SNRs) close to the Galactic Centre. Here we present some of the preliminary results of our 610 and 325 MHz observations.

This paper reviews several aspects of the study of radio emission from Galactic Supernova Remnants (SNRs). The detection of radio emission from SNRs is the most important method for identification of SNRs, and the limitations imposed by selection effects on subsequent statistical studies are discussed. Also discussed are the spectral properties of SNRs, both their integrated spectra, and the evidence for spectral variations across the face of remnants.

Supernova Remnants (SNRs) play essential roles in the dynamics of galaxies by injecting large amounts of energy which can accelerate particles generating cosmic radiation, create large, hot, low density bubbles, and maintain turbulent cloud motions. SNRs shock waves can also compress nearby dense clouds, inducing fragmentation and perhaps collapse into protostars, thus joining the extremes in the life-cycle of stars. The present review illustrates how high quality low frequencies radio observations of galactic SNRs and the surrounding interstellar medium (ISM), can help in the understanding of the many aspects of the nature of the remnants, as well as the consequences of their interaction with the ambient gas.

Low frequency observations at 330 and 74 MHz can provide new insights into supernova remnants (SNR). We can test theoretical predictions for spectral index variations. Nonlinear models of shock acceleration predict that the spectra from young SNR should be slightly concave rather than power laws — flattening toward higher energies. However, few SNR are bright and compact enough to be studied at millimeter wavelengths, restricting studies to the small range from 6 to 20 cm (a factor of 1.7 in electron energies). Observations at 330 MHz increase the electron energy baseline to a factor of 4, while providing sensitivity to larger spatial scales that are resolved out by centimeter-wavelength interferometers. Such observations can also separate thermal from nonthermal emission and detect excess free-free absorption associated with cool gas in remnants. Wide field images also provide an efficient census of both thermal and nonthermal sources over a large region.

We present radio continuum spectra for nearly 200 Galactic supernova remnants (SNRs) from 220 known and included in Green's (1998) catalog. Spectra plotting is an “on—line” procedure of the CATS database http://cats.sao.ru/ and it could plot quite accurate spectra with the thermal plasma free—free absorption in fitting the spectra accounted for: to indicate the presence of extended ionized medium along the line of sight.

We did not find considerable correlation between spectral index and Galactic coordinates l, b of SNRs. An analysis of 190 spectra showed that 78 SNRs (40 %) have clear low-frequency turnover caused, apparently, by absorption in the thermal foreground of the Milky Way. The turnover frequency vτ=1 for these SNRs has mean value near 30 MHz do not correlate with the Galactic coordinates. But the frequency has significant correlation with the distance to SNR, defined from ∑ — D relation.

The observations of the supernova remnant G343.1—2.3 with the Mauritius Radio Telescope, the Australia Compact Array, and the Hobart Single dish are presented. With these more sensitive measurements the association with the pulsar PSR1706-44 becomes much more likely. The major points from the observations are presented.

We report on 74 MHz and 330 MHz VLA observations of the plerionic supernova remnant 3C58. The radio spectral index, α, is uniform across the remnant to within 0.18, indicating a single source for the accelerated electrons. We find no emission from any shell surrounding the remnant. Our 3σ brightness limit on shell emission surrounding 3C58 is < 1.3×10−21 W m−2 Hz−1 sr−1 at 330 MHz.

Radio observations of large Supernova Remnants (SNRs) in the Galaxy are plagued with the problems of confusion and limitations of synthesis telescopes in imaging the emission at large angular scales. Since most SNRs are brighter at low radio frequencies, and the contamination due to thermal emission is reduced, deep and high resolution imaging of Galactic SNRs at meterwave lengths is most useful in their detection and classification. Relatively high resolution and sensitivity over a large range of angular scales provided by the GMRT at meterwave lengths makes it an ideal instrument for detailed multi-frequency imaging of Galactic SNRs.

Radio observational results at 232 MHz and multifrequency studies of supernova remnant (SNR) HB21 are presented in this paper. Both the integrated spectral index and the spatial variations of spectral index of the remnant were calculated by combining the new map at 232 MHz with previously published maps made at 408, 1420, 2695, and 4750 MHz.

We present 610 and 235 MHz GMRT observations of the supernova remnant (SNR) G11.2—0.3 which shows a very large roation measure gradient (ΔRM∼1600 rad m−2) across it. The GMRT observations are the first high-resolution observations of this object at low frequencies. There are differences between the structure observed at 610 and at 235 MHz only some of which can be explained by free-free absorption.

The electron temperatures of the compact cores of the galactic HII regions S206 and S209 have been determined by radio continuum observations near 235, 327 and 610 MHz using the Giant Meterwave Radio Telescope (GMRT). The resolution of our maps are 11″ and 6″ at 327 and 610 MHz respectively. These are the highest resolution low frequency maps of these HII regions.

The results of investigation of the low-frequency cosmic background by the WIND spacecraft near the L1 point during the deepest phase of the last solar activity minimum are presented. The antenna temperature modulation index and the ecliptic longitude of the primary area of radiation for frequencies 260, 516, 772, and 1028 kHz were measured by means of a dipole on the spacecraft which is rotated in ecliptic plane. Our results correct and complement the conclusions of the previous measurements made with IMP-6.

A brief review of Galactic and extragalactic recombination lines of hydrogen at frequencies ≤ 1.4 GHz is presented.