Taking secondary particles produced from dark matter (DM) annihilation process to the origin of the extended diffuse radio emission observed in galaxy clusters, we studied both their morphology and radio spectral profile using simulated Coma like galaxy clusters. We have considered a neutralino annihilation channel dominated by $b\overline b $ species with a branching ratio of 1 and neutralino mass of 35 GeV with annihilation cross-section of 1×10-26 cm3 s-1. The radio emission maps produced for the two simulated galaxy clusters which are based on the MUsic SImulation of galaxy Clusters (MUSIC) dataset reveal the observed radio halo morphology showing radio emission both from the central regions of the cluster and substructures lying out off cluster centre. The flux density curve is in a good agreement for ν ≤ 2 GHz with the obsevational values for the Coma cluster of galaxies showing a small deviation at higher frequencies.

Multi-wavelength emission maps from dark matter (DM) annihilation processes in galaxy clusters are produced using Marenostrum-MultiDark SImulation of galaxy Clusters (MUSIC-2) high resolution cosmological simulations. Comparison made with observational radio emission flux data (spectral shape) and the spatial distribution from the simulated emission maps show that secondary particles from DM annihilation could describe the origin of energetic particles which are the sources of the diffuse radio emission observed in large number of galaxy clusters. DM sub-halos which are dominantly composed of DM, but with very little or no gas and stellar content, are ideal objects to study the nature and properties of DM. Therefore, statistical studies of a large number of them as well the emission maps of high mass-to-light ratio DM sub-halos will not only explain the observed diffused radio emission but also provide very crucial information about the nature and properties of DM particles.

The inverse Compton (IC) limit, TB1012 K, on synchrotron sources places a severe limit on models for intraday variables. The conventional limit is relaxed for proton synchrotron emission, or when acceleration balances IC losses. Coherent emission avoids the limit entirely but introduces other difficulties that have been inadequately discussed.

Statistical information on 8280 individual radio observations of binary stars, predominantly at 8·4 GHz using the Parkes 64 m antenna, is presented. Three main groups are distinguished: (i) RS CVn stars, (ii) classical Algol binaries (EA2s), and (iii) detached pairs of generally early type (ETBs).

The RS CVn stars more frequently gave rise to detectable fluxes, while the ETBs, in these data, are a small and rather heterogeneous class. The Algols' emission appears to increase near conjunction phases, though we cannot clearly distinguish any special property of the Algols' phase-dependent behaviour that is not also shared by the RS CVn binaries. Both these categories' data show a bimodal, phase-dependent pattern to the distribution of detections, suggesting that these binary types share similar underlying physical properties, though there could also be other factors at play. The sample sizes of the Algols and particularly the ETB detections are too small for effective, discriminatory statistics, however.

AE Aqr is a cataclysmic variable consisting of a magnetised white dwarf with a spin period of 33 s, and a K-dwarf companion. Because of the rapid spin the magnetosphere of the white dwarf the matter that is flowing over from the secondary cannot accrete onto the white dwarf, and rather it is ejected from the system. AE Aqr is subject to extended flaring activity at all wavelengths from radio via optical to X-rays. I present observations of AE Aqr at 345 and 850 GHz using the LABOCA and SABOCA bolometers on APEX. These observations are good enough to distinguish individual flares at both 345 and 850 GHz, and the SABOCA observation is the first measurement of the system at 850 GHz.

This article describes the observations of a type III radio burst observed at 103 MHz simultaneously by the two radio telescopes situated at Rajkot (22.3°N, 70.7°E) and Thaltej (23°N, 72.4°E). This event occurred on September 30, 1993 at about 0430 UT and lasted for only half a minute. The event consisted of several sharp spikes in a group. The rise and fall time of these are comparable, however the peaks of individual spikes varied by a factor of four. The comparison of these observations with the data of solar radio spectrograph HiRAS indicates that this was a metric radio burst giving highest emission at about 103 MHz.

We review the existing literature on the coronal disconnection events (CDEs) and discuss the importance of these events in understanding coronal structures. We discuss the possible radio signatures of the CDEs and how they may be observed by radio instruments.

New observations of the colliding wind Wolf-Rayet WC7+O4-5 binary WR140 (HD 193793) at 6 cm and 21 cm with the Westerbork Synthesis Radio Telescope are presented. They show that the 21 cm flux, in particular, rose to a sharp maximum in 1992, lagging about a year behind the 6 cm flux. After maximum, both fell simultaneously. The data are interpreted in terms of the varying circumstellar extinction to a non-thermal source in the wind interaction region due to the winds of both WC and O stars.