ABSTRACT
We present MeerKAT 1.28 GHz total-intensity, polarization, and spectral-index images covering the giant (projected length l ≈ 1.57 Mpc) X-shaped radio source PKS 2014−55 with an ...unprecedented combination of brightness sensitivity and angular resolution. They show the clear ‘double boomerang’ morphology of hydrodynamical backflows from the straight main jets deflected by the large and oblique hot-gas halo of the host galaxy PGC 064440. The magnetic field orientation in PKS 2014−55 follows the flow lines from the jets through the secondary wings. The radio source is embedded in faint ($T_\mathrm{b} \approx 0.5 \mathrm{\, K}$) cocoons having the uniform brightness temperature and sharp outer edges characteristic of subsonic expansion into the ambient intragroup medium. The position angle of the much smaller (l ∼ 25 kpc) restarted central source is within 5° of the main jets, ruling out models that invoke jet re-orientation or two independent jets. Compression and turbulence in the backflows probably produce the irregular and low polarization bright region behind the apex of each boomerang as well as several features in the flow with bright heads and dark tails.
A number of exciting new telescopes as well as enhancements of existing ones have either come or will come into operation in the near future. In the radio window of the electromagnetic spectrum, the ...Square Kilometer Array (SKA), being built in both South Africa and Australia, is one of the most exciting telescopes. It will help address some of the key astrophysical questions of the day. This article gives an overview of SKA, the scientific questions it will address and highlights a few early results from MeerKAT, a SKA precursor radio telescope built in South Africa that will be integrated with SKA.
Circinus X-1 is a bright and highly variable X-ray binary which displays strong and rapid evolution in all wavebands. Radio flaring, associated with the production of a relativistic jet, occurs ...periodically on a ∼17-d time-scale. A longer term envelope modulates the peak radio fluxes in flares, ranging from peaks in excess of a Jansky in the 1970s to a historic low of milliJanskys during the years 1994-2006. Here, we report first observations of this source with the MeerKAT (Karoo Array Telescope) test array, KAT-7, part of the pathfinder development for the African dish component of the Square Kilometre Array, demonstrating successful scientific operation for variable and transient sources with the test array. The KAT-7 observations at 1.9 GHz during the period 2011 December 13 to 2012 January 16 reveal in temporal detail the return to the Jansky-level events observed in the 1970s. We compare these data to contemporaneous single-dish measurements at 4.8 and 8.5 GHz with the HartRAO 26-m telescope and X-ray monitoring from MAXI. We discuss whether the overall modulation and recent dramatic brightening is likely to be due to an increase in the power of the jet due to changes in accretion rate or changing Doppler boosting associated with a varying angle to the line of sight.
The relative positions of the high and low brightness regions in the extra-galactic sources in the 3CR complete sample are found to be correlated with the luminosity of these sources.
The advent of international wideband communication by optical fibre has produced a revolution in communications and the use of the internet. Many African countries are now connected to undersea fibre ...linking them to other African countries and to other continents. Previously international communication was by microwave links through geostationary satellites. These are becoming redundant in some countries as optical fibre takes over, as this provides 1000 times the bandwidth of the satellite links. In the 1970's and 1980's some two dozen large (30 m diameter class) antennas were built in various African countries to provide the satellite links. Twenty six are currently known in 19 countries. As these antennas become redundant, the possibility exists to convert them for radio astronomy at a cost of roughly one tenth that of a new antenna of similar size. HartRAO, SKA Africa and the South African Department of Science and Technology (DST) have started exploring this possibility with some of the African countries.
We have undertaken a systematic study of FRI and FRII radio galaxies with the upgraded Giant Metrewave Radio Telescope (uGMRT) and MeerKAT. The main goal is to explore whether the unprecedented few ...\(\mu\)Jy sensitivity reached in the range 550-1712 MHz at the resolution of \(\sim4^{\prime\prime}-7^{\prime\prime}\) reveals new features in the radio emission which might need us to revise our current classification scheme for classical radio galaxies. In this paper we present the results for the first set of four radio galaxies, i.e. 4C 12.02, 4C 12.03, CGCG 044-046 and CGCG 021-063. The sources have been selected from the 4C sample with well-defined criteria, and have been imaged with the uGMRT in the range 550-850 MHz (band 4) and with the MeerKAT in the range 856-1712 MHz (L-band). Full resolution images are presented for all sources in the sample, together with MeerKAT in-band spectral images. Additionally, the uGMRT-MeerKAT spectral image and MeerKAT L-band polarisation structure are provided for CGCG 044-046. Our images contain a wealth of morphological details, such as filamentary structure in the emission from the lobes, radio emission beyond the hot-spots in three sources, and misalignments. We briefly discuss the overall properties of CGCG 044-046 in the light of the local environment as well, and show possible restarted activity in 4C 12.03 which needs to be confirmed. We conclude that at least for the sources presented here, the classical FRI/FRII morphological classification still holds with the current improved imaging capabilities, but the richness in details also suggests caution in the systematic morphological classification carried out with automatic procedures in surveys with poorer sensitivity and angular resolution.
The inner \(\sim\)200 pc region of the Galaxy contains a 4 million M\(_{\odot}\) supermassive black hole (SMBH), significant quantities of molecular gas, and star formation and cosmic ray energy ...densities that are roughly two orders of magnitude higher than the corresponding levels in the Galactic disk. At a distance of only 8.2 kpc, the region presents astronomers with a unique opportunity to study a diverse range of energetic astrophysical phenomena, from stellar objects in extreme environments, to the SMBH and star-formation driven feedback processes that are known to influence the evolution of galaxies as a whole. We present a new survey of the Galactic center conducted with the South African MeerKAT radio telescope. Radio imaging offers a view that is unaffected by the large quantities of dust that obscure the region at other wavelengths, and a scene of striking complexity is revealed. We produce total intensity and spectral index mosaics of the region from 20 pointings (144 hours on-target in total), covering 6.5 square degrees with an angular resolution of 4\("\),at a central frequency of 1.28 GHz. Many new features are revealed for the first time due to a combination of MeerKAT's high sensitivity, exceptional \(u,v\)-plane coverage, and geographical vantage point. We highlight some initial survey results, including new supernova remnant candidates, many new non-thermal filament complexes, and enhanced views of the Radio Arc Bubble, Sgr A and Sgr B regions. This project is a SARAO public legacy survey, and the image products are made available with this article.
We present MeerKAT 1.28 GHz total-intensity, polarization, and spectral-index images covering the giant (projected length \(l \approx 1.57\)~Mpc) X-shaped radio source PKS~2014\(-\)55 with an ...unprecedented combination of brightness sensitivity and angular resolution. They show the clear "double boomerang" morphology of hydrodynamical backflows from the straight main jets deflected by the large and oblique hot-gas halo of the host galaxy PGC~064440. The magnetic field orientation in PKS~2014\(-\)55 follows the flow lines from the jets through the secondary wings. The radio source is embedded in faint (\(T_\mathrm{b} \approx 0.5 \mathrm{\,K}\)) cocoons having the uniform brightness temperature and sharp outer edges characteristic of subsonic expansion into the ambient intra-group medium. The position angle of the much smaller (\(l \sim 25\)~kpc) restarted central source is within \(5^\circ\) of the main jets, ruling out models that invoke jet re-orientation or two independent jets. Compression and turbulence in the backflows probably produce the irregular and low polarization bright region behind the apex of each boomerang as well as several features in the flow with bright heads and dark tails.
We present the confusion-limited 1.28 GHz MeerKAT DEEP2 image covering one \(\approx 68'\) FWHM primary beam area with \(7.6''\) FWHM resolution and \(0.55 \pm 0.01\) \(\mu\)Jy/beam rms noise. Its ...J2000 center position \(\alpha=04^h 13^m 26.4^s\), \(\delta=-80^\circ 00' 00''\) was selected to minimize artifacts caused by bright sources. We introduce the new 64-element MeerKAT array and describe commissioning observations to measure the primary beam attenuation pattern, estimate telescope pointing errors, and pinpoint \((u,v)\) coordinate errors caused by offsets in frequency or time. We constructed a 1.4 GHz differential source count by combining a power-law count fit to the DEEP2 confusion \(P(D)\) distribution from \(0.25\) to \(10\) \(\mu\)Jy with counts of individual DEEP2 sources between \(10\) \(\mu\)Jy and \(2.5\) mJy. Most sources fainter than \(S \sim 100\) \(\mu\)Jy are distant star-forming galaxies obeying the FIR/radio correlation, and sources stronger than \(0.25\) \(\mu\)Jy account for \(\sim93\%\) of the radio background produced by star-forming galaxies. For the first time, the DEEP2 source count has reached the depth needed to reveal the majority of the star formation history of the universe. A pure luminosity evolution of the 1.4 GHz local luminosity function consistent with the Madau & Dickinson (2014) model for the evolution of star-forming galaxies based on UV and infrared data underpredicts our 1.4 GHz source count in the range \(-5 \lesssim \logS(\mathrm{Jy}) \lesssim -4\).
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