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Register a new userEngineering and Science Highlights of the KAT-7 Radio Telescope
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The construction of the KAT-7 array in the Karoo region of the Northern Cape in South Africa was intended primarily as an engineering prototype for technologies and techniques applicable to the MeerKAT telescope. This paper looks at the main engineering and scien- tific highlights from this effort, and discusses their applicability to both MeerKAT and other next-generation radio telescopes. In particular we found that the composite dish surface works well, but it becomes complicated to fabricate for a dish lacking circular symmetry; the Stir- ling cycle cryogenic system with ion pump to achieve vacuum works but demands much higher maintenance than an equivalent Gifford-McMahon cycle system; the ROACH (Recon- figurable Open Architecture Computing Hardware)-based correlator with SPEAD (Stream- ing Protocol for Exchanging Astronomical Data) protocol data transfer works very well and KATCP (Karoo Array Telescope Control Protocol) control protocol has proven very flexible and convenient. KAT-7 has also been used for scientific observations where it has a niche in mapping low surface-brightness continuum sources, some extended HI halos and OH masers in star-forming regions. It can also be used to monitor continuum source variability, observe pulsars, and make VLBI observations
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We detect a new suspected giant radio galaxy (GRG) discovered by KAT-7. The GRG core is identified with the WISE source J013313.50-130330.5, an extragalactic source based on its infrared colors and consistent with a misaligned AGN-type spectrum at $zapprox 0.3$. The multi-$ u$ spectral energy distribution (SED) of the object associated to the GRG core shows a synchrotron peak at $ u approx 10^{14}$ Hz consistent with the SED of a radio galaxy blazar-like core. The angular size of the lobes are $sim 4 ^{prime}$ for the NW lobe and $sim 1.2 ^{prime}$ for the SE lobe, corresponding to projected linear distances of $sim 1078$ kpc and $sim 324$ kpc, respectively. The best-fit parameters for the SED of the GRG core and the value of jet boosting parameter $delta =2$, indicate that the GRG jet has maximum inclination $theta approx 30$ deg with respect to the line of sight, a value obtained for $delta=Gamma$, while the minimum value of $theta$ is not constrained due to the degeneracy existing with the value of Lorentz factor $Gamma$. Given the photometric redshift $z approx 0.3$, this GRG shows a core luminosity of $P_{1.4 GHz} approx 5.52 times 10^{24}$ W Hz$^{-1}$, and a luminosity $P_{1.4 GHz} approx 1.29 times 10^{25}$ W Hz$^{-1}$ for the NW lobe and $P_{1.4 GHz} approx 0.46 times 10^{25}$ W Hz$^{-1}$ for the SE lobe, consistent with the typical GRG luminosities. The radio lobes show a fractional linear polarization $approx 9 %$ consistent with typical values found in other GRG lobes.
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-day timescale. A longer-term envelope modulates the peak radio fluxes in flares, ranging from peaks in excess of a Jansky in the 1970s to an historic low of milliJanskys during the years 1994 to 2007. Here we report first observations of this source with the MeerKAT test array, KAT-7, part of the pathfinder development for the African dish component of the Square Kilometre Array (SKA), demonstrating successful scientific operation for variable and transient sources with the test array. The KAT-7 observations at 1.9 GHz during the period 13 December 2011 to 16 January 2012 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.
HI observations of the Magellanic-type spiral NGC 3109, obtained with the seven dish Karoo Array Telescope (KAT-7), are used to analyze its mass distribution. Our results are compared to what is obtained using VLA data. KAT-7 is the precursor of the SKA pathfinder MeerKAT, which is under construction. The short baselines and low system temperature of the telescope make it sensitive to large scale low surface brightness emission. The new observations with KAT-7 allow the measurement of the rotation curve of NGC 3109 out to 32, doubling the angular extent of existing measurements. A total HI mass of 4.6 x 10^8 Msol is derived, 40% more than what was detected by the VLA observations. The observationally motivated pseudo-isothermal dark matter (DM) halo model can reproduce very well the observed rotation curve but the cosmologically motivated NFW DM model gives a much poorer fit to the data. While having a more accurate gas distribution has reduced the discrepancy between the observed RC and the MOdified Newtonian Dynamics (MOND) models, this is done at the expense of having to use unrealistic mass-to-light ratios for the stellar disk and/or very large values for the MOND universal constant a0. Different distances or HI contents cannot reconcile MOND with the observed kinematics, in view of the small errors on those two quantities. As for many slowly rotating gas-rich galaxies studied recently, the present result for NGC 3109 continues to pose a serious challenge to the MOND theory.
We describe the design and performance of the Engineering Development Array (EDA), which is a low frequency radio telescope comprising 256 dual-polarisation dipole antennas working as a phased-array. The EDA was conceived of, developed, and deployed in just 18 months via re-use of Square Kilometre Array (SKA) precursor technology and expertise, specifically from the Murchison Widefield Array (MWA) radio telescope. Using drift scans and a model for the sky brightness temperature at low frequencies, we have derived the EDAs receiver temperature as a function of frequency. The EDA is shown to be sky-noise limited over most of the frequency range measured between 60 and 240 MHz. By using the EDA in interferometric mode with the MWA, we used calibrated visibilities to measure the absolute sensitivity of the array. The measured array sensitivity matches very well with a model based on the array layout and measured receiver temperature. The results demonstrate the practicality and feasibility of using MWA-style precursor technology for SKA-scale stations. The modular architecture of the EDA allows upgrades to the array to be rolled out in a staged approach. Future improvements to the EDA include replacing the second stage beamformer with a fully digital system, and to transition to using RF-over-fibre for the signal output from first stage beamformers.
Observations of extrasolar planets were not projected to be a significant part of the Spitzer Space Telescopes mission when it was conceived and designed. Nevertheless, Spitzer was the first facility to detect thermal emission from a hot Jupiter, and the range of Spitzers exoplanetary investigations grew to encompass transiting planets, microlensing, brown dwarfs, and direct imaging searches and astrometry. Spitzer used phase curves to measure the longitudinal distribution of heat as well as time-dependent heating on hot Jupiters. Spitzers secondary eclipse observations strongly constrained the dayside thermal emission spectra and corresponding atmospheric compositions of hot Jupiters, and the timings of eclipses were used for studies of orbital dynamics. Spitzers sensitivity to carbon-based molecules such as methane and carbon monoxide was key to atmospheric composition studies of transiting exoplanets as well as imaging spectroscopy of brown dwarfs, and complemented Hubble spectroscopy at shorter wavelengths. Spitzers capability for long continuous observing sequences enabled searches for new transiting planets around cool stars, and helped to define the architectures of planetary systems like TRAPPIST-1. Spitzer measured masses for small planets at large orbital distances using microlensing parallax. Spitzer observations of brown dwarfs probed their temperatures, masses, and weather patterns. Imaging and astrometry from Spitzer was used to discover new planetary mass brown dwarfs and to measure distances and space densities of many others.
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