Propagation of the radio waves from distant compact radio sources through turbulent interstellar plasma in our Galaxy leads to twinkling of these sources, a phenomenon called interstellar scintillation. Such scintillations are a unique probe of the micro-arcsecond structure of radio sources as well as of the sub-AU-scale structure of the Galactic interstellar medium. Weak scintillations (i.e. intensity modulation of a few per cent) on timescales of a few days or longer are commonly seen at centimetre wavelengths and are thought to result from the line-of-sight integrated turbulence in the Milky Way's interstellar plasma. So far, only three sources were known that show more extreme variations, with modulations at the level of tens of per cent on timescales less than an hour. This requires propagation through nearby (d<~10pc) anomalously dense (n_e_>10^2^cm^3^) plasma clouds. Here we report the discovery with Apertif of a source (J1402+5347) showing extreme (~50%) and rapid variations on a timescale of just 6.5 minutes in the decimetre band (1.4GHz). The spatial scintillation pattern is highly anisotropic with a semi-minor axis of about 20,000 km. Canonical theory of refractive scintillation constrains the scattering plasma to be within the Oort cloud. The sight-line to J1402+5347 however passes unusually close to the B3 star Alkaid (eta UMa) at a distance of 32pc. If the scintillations are associated with Alkaid, then the angular size of J1402+5347 along the minor-axis of the scintels must be smaller than 10 microarcseconds yielding an apparent brightness temperature for an isotropic source of >10^14^K.
A complete sample of core-dominated radio sources has been studied using the interplanetary-scintillation method. In total, 72 sources were observed, with scintillations detected in 28 of them. The remaining sources have upper limits on their flux densities. Integrated flux densities are estimated for 24 sources. Cut-offs have been observed in the spectra of many sources. The thermal-electron densities have been estimated, assuming that these cut-offs are due to free-free absorption of the synchrotron radio emission.
A complete sample of radio sources has been studied using the interplanetary scintillation method. In total, 32 sources were observed, with scintillations detected in 12 of them. The remaining sources have upper limits for the flux densities of their compact components. Integrated flux densities are estimated for 18 sources.
We present an analysis of the energetics and particle content of the lobes of 24 radio galaxies at the cores of cooling clusters. The radio lobes in these systems have created visible cavities in the surrounding hot, X-ray-emitting gas, which allow direct measurement of the mechanical jet power of radio sources over six decades of radio luminosity, independently of the radio properties themselves. We find that jet (cavity) power increases with radio synchrotron power approximately as P_jet_~L^{beta}^_radio_, where 0.35<={beta}<=0.70 depending on the bandpass of measurement and state of the source. Furthermore, we place limits on the magnetic field strengths and particle content of the radio lobes using a variety of X-ray constraints. We find that the lobe magnetic field strengths vary between a few to several tens of microgauss depending on the age and dynamical state of the lobes.
The results of 0.97, 2.3, 3.9, 7.7, 11.1 and 21.7GHz observations of a complete sample of radio sources obtained on the RATAN-600 radio telescope are presented. The sample is comprised of sources from the 4.85-GHz MGB survey, and contains all sources at declinations 10-12.5 degrees (J2000) with galactic latitudes |b|>15 degrees and flux densities S(4.85)>200mJy. Optical identifications have been obtained for about 86% of the radio sources with flat spectra and 59% of those with steep spectra.
The Abell clusters 2125 and 2645 have different radio source populations, despite being very similar in richness (Abell class 4) and redshift (0.25). The number density of radio sources in Abell 2125 is almost an order of magnitude more than that in Abell 2645, based on observations to the same optical and radio luminosities of the two clusters. About 30% of the radio sources in Abell 2125 shows signs of star formation, with the largest concentration of them in the southwest clump 2Mpc from the cluster center.
We present a VLA C-configuration imaging survey of 14 rich Abell clusters. The observations were undertaken with the intent of characterizing the galaxy orbits within the cluster by combining galaxy redshifts with indicators of orbital shape. We present maps of the observed clusters, detailed maps of resolved sources detected in the survey, comparisons with optical images of the clusters, and tables of source parameters for all detected sources with measured flux values.
Statistically complete samples comprising 33 bright spiral galaxies that are strong radio sources were selected. Sixteen of the galaxies have integrated radio-to-optical flux ratios greater than 10 times the median value for normal spirals. The remainder contain radio cores <=20" in size and stronger than 90mJy at 1415MHz or 60mJy at 2695MHz. High-resolution (2" at 1413MHz or 0.6" at 4885MHz) maps of these galaxies were made with the Very Large Array. The radio sources are usually confined to the central 1kpc of the galaxies, lying within and extending parallel to their stellar disks. There is no evidence for ejection from central components. Most of the sources appear to be coextensive with regions of intense star formation (bolometric luminosities ~10^10-10^11L_{Sun}). The typical radio luminosity, ~10^21^W/Hz/sr at 1413MHz, of the resolved sources can be explained by synchrotron radiation from supernova remnants (SNRs) produced at the rate of ~1/yr. Five of the radio sources are <=1pc in size and probably are not related to star formation or SNRs. The radio and 10-{mu}m flux densities of the extended sources are roughly proportional. The bolometric mass-to luminosity ratios in some active regions are too low to have been maintained for a Hubble time. Nearly all of the strong, extended radio sources are found in galaxies with nearby companions, so most of the episodic bursts of star formation are apparently triggered by galaxy-galaxy interactions.
We present a catalogue of the 408MHz and 1420MHz radio sources in the region centered near Right Ascension 4h58m and Declination 46degrees (epoch 1950), i.e. near the supernova remnant HB9. The observations were made with the Synthesis Telescope at the Dominion Radio Astrophysical Observatory, near Penticton, Canada. 494 sources at 408MHz and 255 sources at 1420MHz were detected. 408-1420MHz spectral indices for 101 common sources were derived. The 408MHz source list was compared with the 4850MHz sources from the Green Bank catalog. Spectral indices were determined for 165 common sources. We also compared the source lists with the IRAS and ROSAT point source catalogs for that region and have identified 16 radio sources with IRAS point sources and 3 radio sources with X-ray sources.
18 days of MERLIN data and 42h of A-array VLA data at 1.4GHz have been combined to image a 10-arcmin field centred on the Hubble Deep Field (HDF). This area also includes the Hubble Flanking Fields (HFF). A complete sample of 92 radio sources with S1.4>40{mu}Jy was detected using the VLA data alone and then imaged with the MERLIN+VLA combination. The combined images offer (i) higher angular resolution (synthesized beams of diameter 0.2-0.5arcsec), (ii) improved astrometric accuracy, and (iii) improved sensitivity compared with VLA-only data.
