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An FPGA-based digital-receiver has been developed for a low-frequency imaging radio interferometer, the Murchison Widefield Array (MWA). The MWA, located at the Murchison Radio-astronomy Observatory (MRO) in Western Australia, consists of 128 dual-polarized aperture-array elements (tiles) operating between 80 and 300\,MHz, with a total processed bandwidth of 30.72 MHz for each polarization. Radio-frequency signals from the tiles are amplified and band limited using analog signal conditioning units; sampled and channelized by digital-receivers. The signals from eight tiles are processed by a single digital-receiver, thus requiring 16 digital-receivers for the MWA. The main function of the digital-receivers is to digitize the broad-band signals from each tile, channelize them to form the sky-band, and transport it through optical fibers to a centrally located correlator for further processing. The digital-receiver firmware also implements functions to measure the signal power, perform power equalization across the band, detect interference-like events, and invoke diagnostic modes. The digital-receiver is controlled by high-level programs running on a single-board-computer. This paper presents the digital-receiver design, implementation, current status, and plans for future enhancements., Comment: 14 pages, 7 figures

[1] Having an accurate method to estimate and remove ionospheric effects is a major issue for low-frequency radio astronomy arrays, as the ionosphere is one of their largest error terms. One way to estimate the ionosphere is to measure total electron content (TEC) using dual frequency global positioning system (GPS) signals. This technique uses the dispersive nature of the ionosphere, as both group and phase velocities are (to first order) dependent on the inverse square of the frequency and on TEC. Using these properties, TEC can be measured to a high degree of accuracy by computing the delay difference between signals at GPS's two frequencies (L1 = 1575.42 and L2 = 1227.6 MHz). Unfortunately, effects other than ionospheric dispersion also introduce differential delay differences. These additional differences, called biases, can be separated into those introduced by the satellite and those by the receiver. Receiver biases show the most significant variations, sometimes over intervals of hours. Changing temperature conditions at the receiver antenna, along the cable, or in the internal receiver hardware are thought to be responsible for some of these variations. We report here on an investigation of the temperature dependence of the GPS receiver bias. Our results show that for our particular receiver, antenna, and cable set-up, a temperature-dependent bias is clearly evident, and that this temperature dependence varies from receiver to receiver. When the receiver bias temperature dependence is removed, a noise level of 1–3 TEC units still remains in the bias estimation.

Using the final 128 antenna locations of the Murchison Widefield Array (MWA), we calculate its sensitivity to the epoch of reionization (EoR) power spectrum of redshifted 21 cm emission for a fiducial model and provide the tools to calculate the sensitivity for any model. Our calculation takes into account synthesis rotation, chromatic and asymmetrical baseline effects, and excludes modes that will be contaminated by foreground subtraction. For the fiducial model, the MWA will be capable of a 14σ detection of the EoR signal with one full season of observation on two fields (900 and 700 h)., National Science Foundation (U.S.) (Grant AST CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant AST-0908884), National Science Foundation (U.S.) (Grant PHY-0835713), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science

Antenna layout is an important design consideration for radio interferometers because it determines the quality of the snapshot point spread function (PSF, or array beam). This is particularly true for experiments targeting the 21 cm Epoch of Reionization signal as the quality of the foreground subtraction depends directly on the spatial dynamic range and thus the smoothness of the baseline distribution. Nearly all sites have constraints on where antennas can be placed---even at the remote Australian location of the MWA (Murchison Widefield Array) there are rock outcrops, flood zones, heritages areas, emergency runways and trees. These exclusion areas can introduce spatial structure into the baseline distribution that enhance the PSF sidelobes and reduce the angular dynamic range. In this paper we present a new method of constrained antenna placement that reduces the spatial structure in the baseline distribution. This method not only outperforms random placement algorithms that avoid exclusion zones, but surprisingly outperforms random placement algorithms without constraints to provide what we believe are the smoothest constrained baseline distributions developed to date. We use our new algorithm to determine antenna placements for the originally planned MWA, and present the antenna locations, baseline distribution, and snapshot PSF for this array choice.

We are developing the Precision Array for Probing the Epoch of Reionization (PAPER) to detect 21cm emission from the early Universe, when the first stars and galaxies were forming. We describe the overall experiment strategy and architecture and summarize two PAPER deployments: a 4-antenna array in the low-RFI environment of Western Australia and an 8-antenna array at our prototyping site in Green Bank, WV. From these activities we report on system performance, including primary beam model verification, dependence of system gain on ambient temperature, measurements of receiver and overall system temperatures, and characterization of the RFI environment at each deployment site. We present an all-sky map synthesized between 139 MHz and 174 MHz using data from both arrays that reaches down to 80 mJy (4.9 K, for a beam size of 2.15e-5 steradians at 154 MHz), with a 10 mJy (620 mK) thermal noise level that indicates what would be achievable with better foreground subtraction. We calculate angular power spectra ($C_\ell$) in a cold patch and determine them to be dominated by point sources, but with contributions from galactic synchrotron emission at lower radio frequencies and angular wavemodes. Although the cosmic variance of foregrounds dominates errors in these power spectra, we measure a thermal noise level of 310 mK at $\ell=100$ for a 1.46-MHz band centered at 164.5 MHz. This sensitivity level is approximately three orders of magnitude in temperature above the level of the fluctuations in 21cm emission associated with reionization.

Stress within the teaching profession has a negative impact on the health and well-being of individual teachers and on retention and recruitment for the profession as a whole. There is increasing literature to suggest that Mindfulness is a useful intervention to address a variety of psychological problems, and that Mindfulness-Based Stress Reduction (MBSR) is a particularly helpful intervention for stress. We investigated the effects of teaching a MBSR course to primary school teachers to reduce stress. The MBSR course was taught to a group of primary school teachers and evaluated to establish its effects on levels of anxiety, depression, and stress, as well as movement towards a stated goal and changes in awareness. The results showed improvement for most participants for anxiety, depression, and stress, some of which were statistically significant. There were also significant improvements on two of the four dimensions of a mindfulness skills inventory. These results suggest that this approach could be a potentially cost-effective method to combat teacher stress and burnout.

Experiments were performed with prototype antenna tiles for the Mileura Widefield Array--Low Frequency Demonstrator (MWA-LFD) to better understand the widefield, wideband properties of their design and to characterize the radio frequency interference (RFI) between 80 and 300 MHz at the site in Western Australia. Observations acquired during the six month deployment confirmed the predicted sensitivity of the antennas, sky-noise dominated system temperatures, and phase-coherent interferometric measurements. The radio spectrum is remarkably free of strong terrestrial signals, with the exception of two narrow frequency bands allocated to satellite downlinks and rare bursts due to ground-based transmissions being scattered from aircraft and meteor trails. Results indicate the potential of the MWA-LFD to make significant achievements in its three key science objectives: epoch of reionziation science, heliospheric science, and radio transient detection., Accepted by AJ. 17 pages with figures

The Murchison Widefield Array (MWA) is a Square Kilometre Array (SKA) Precursor. The telescope is located at the Murchison Radio--astronomy Observatory (MRO) in Western Australia (WA). The MWA consists of 4096 dipoles arranged into 128 dual polarisation aperture arrays forming a connected element interferometer that cross-correlates signals from all 256 inputs. A hybrid approach to the correlation task is employed, with some processing stages being performed by bespoke hardware, based on Field Programmable Gate Arrays (FPGAs), and others by Graphics Processing Units (GPUs) housed in general purpose rack mounted servers. The correlation capability required is approximately 8 TFLOPS (Tera FLoating point Operations Per Second). The MWA has commenced operations and the correlator is generating 8.3 TB/day of correlation products, that are subsequently transferred 700 km from the MRO to Perth (WA) in real-time for storage and offline processing. In this paper we outline the correlator design, signal path, and processing elements and present the data format for the internal and external interfaces., Comment: 17 pages, 9 figures. Accepted for publication in PASA. Some figures altered to meet astro-ph submission requirements

We present a search for transient and variable radio sources at 154 MHz with the Murchison Widefield Array 32-tile prototype. 51 images were obtained that cover a field of view of 1430 deg[superscript 2] centred on Hydra A. The observations were obtained over three days in 2010 March and three days in 2011 April and May. The mean cadence of the observations was 26 min and there was additional temporal information on day and year time-scales. We explore the variability of a sample of 105 low-frequency radio sources within the field. Four bright (S > 6 Jy) candidate variable radio sources were identified that displayed low levels of short time-scale variability (26 min). We conclude that this variability is likely caused by simplifications in the calibration strategy or ionospheric effects. On the time-scale of 1 yr we find two sources that show significant variability. We attribute this variability to either refractive scintillation or intrinsic variability. No radio transients were identified and we place an upper limit on the surface density of sources ρ < 7.5 × 10[superscript −5] deg[superscript −2] with flux densities >5.5 Jy, and characteristic time-scales of both 26 min and 1 yr., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), National Science Foundation (U.S.) (Grant CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0908884), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science

The Murchison Widefield Array is a low frequency (80 – 300 MHz) SKA Precursor, comprising 128 aperture array elements (known as tiles) distributed over an area of 3 km diameter. The MWA is located at the extraordinarily radio quiet Murchison Radioastronomy Observatory in the mid-west of Western Australia, the selected home for the Phase 1 and Phase 2 SKA low frequency arrays. The MWA science goals include: 1) detection of fluctuations in the brightness temperature of the diffuse redshifted 21 cm line of neutral hydrogen from the epoch of reionisation; 2) studies of Galactic and extragalactic processes based on deep, confusion-limited surveys of the full sky visible to the array; 3) time domain astrophysics through exploration of the variable radio sky; and 4) solar imaging and characterisation of the heliosphere and ionosphere via propagation effects on background radio source emission. This paper concentrates on the capabilities of the MWA for solar science and summarises some of the solar science results to date, in advance of the initial operation of the final instrument in 2013., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant CAREER-0847753), National Science Foundation (U.S.) (Grant PHY-0835713), National Science Foundation (U.S.) (Grant AST-0908884), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science

The Murchison Widefield Array (MWA) is a new low frequency interferomeric radio telescope. The MWA is the low frequency precursor to the Square Kilometre Array (SKA) and is the first of three SKA precursors to be operational, supporting a varied science mission ranging from the attempted detection of the Epoch of Reionisation to the monitoring of solar flares and space weather. We explore the possibility that the MWA can be used for the purposes of Space Situational Awareness (SSA). In particular we propose that the MWA can be used as an element of a passive radar facility operating in the frequency range 87.5 - 108 MHz (the commercial FM broadcast band). In this scenario the MWA can be considered the receiving element in a bi-static radar configuration, with FM broadcast stations serving as non-cooperative transmitters. The FM broadcasts propagate into space, are reflected off debris in Earth orbit, and are received at the MWA. The imaging capabilities of the MWA can be used to simultaneously detect multiple pieces of space debris, image their positions on the sky as a function of time, and provide tracking data that can be used to determine orbital parameters. Such a capability would be a valuable addition to Australian and global SSA assets, in terms of southern and eastern hemispheric coverage. We provide a feasibility assessment of this proposal, based on simple calculations and electromagnetic simulations that shows the detection of sub-metre size debris should be possible (debris radius of >0.5 m to ~1000 km altitude). We also present a proof-of-concept set of observations that demonstrate the feasibility of the proposal, based on the detection and tracking of the International Space Station via reflected FM broadcast signals originating in south-west Western Australia. These observations broadly validate our calculations and simulations., 24 pages, 5 figures, accepted by The Astronomical Journal. Abstract abridged here due to character number limits

We present new wide-field observations of Centaurus A (Cen A) and the surrounding region at 118 MHz with the Murchison Widefield Array (MWA) 32-tile prototype, with which we investigate the spectral-index distribution of Cen A's giant radio lobes. We compare our images to 1.4 GHz maps of Cen A and compute spectral indices using temperature–temperature plots and spectral tomography. We find that the morphologies at 118 MHz and 1.4 GHz match very closely apart from an extra peak in the southern lobe at 118 MHz, which provides tentative evidence for the existence of a southern counterpart to the northern middle lobe of Cen A. Our spatially averaged spectral indices for both the northern and southern lobes are consistent with previous analyses, however we find significant spatial variation of the spectra across the extent of each lobe. Both the spectral-index distribution and the morphology at low radio frequencies support a scenario of multiple outbursts of activity from the central engine. Our results are consistent with inverse-Compton modelling of radio and gamma-ray data that support a value for the lobe age of between 10 and 80 Myr., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), National Science Foundation (U.S.) (Grant CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0908884), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science

Significant new opportunities for astrophysics and cosmology have been identified at low radio frequencies. The Murchison Widefield Array is the first telescope in the southern hemisphere designed specifically to explore the low-frequency astronomical sky between 80 and 300 MHz with arcminute angular resolution and high survey efficiency. The telescope will enable new advances along four key science themes, including searching for redshifted 21-cm emission from the EoR in the early Universe; Galactic and extragalactic all-sky southern hemisphere surveys; time-domain astrophysics; and solar, heliospheric, and ionospheric science and space weather. The Murchison Widefield Array is located in Western Australia at the site of the planned Square Kilometre Array (SKA) low-band telescope and is the only low-frequency SKA precursor facility. In this paper, we review the performance properties of the Murchison Widefield Array and describe its primary scientific objectives., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), National Science Foundation (U.S.) (Grant CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0908884), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science

The Murchison Widefield Array is a low frequency (80 - 300 MHz) SKA Precursor, comprising 128 aperture array elements distributed over an area of 3 km diameter. The MWA is located at the extraordinarily radio quiet Murchison Radioastronomy Observatory in the mid-west of Western Australia, the selected home for the Phase 1 and Phase 2 SKA low frequency arrays. The MWA science goals include: 1) detection of fluctuations in the brightness temperature of the diffuse redshifted 21 cm line of neutral hydrogen from the epoch of reionisation; 2) studies of Galactic and extragalactic processes based on deep, confusion-limited surveys of the full sky visible to the array; 3) time domain astrophysics through exploration of the variable radio sky; and 4) solar imaging and characterisation of the heliosphere and ionosphere via propagation effects on background radio source emission. This paper will focus on a brief discussion of the as-built MWA system, highlighting several novel characteristics of the instrument, and a brief progress report (as of June 2012) on the final construction phase. Practical completion of the MWA is expected in November 2012, with commissioning commencing from approximately August 2012 and operations commencing near mid 2013. A brief description of recent science results from the MWA prototype instrument is given., 8 pages, Resolving the Sky - Radio Interferometry: Past, Present and Future - RTS2012, April 17-20, 2012, Manchester, UK

[1] Midlatitude space weather events are being monitored at a location in Western Australia (−26.7° latitude, 116.7° longitude, and −38° magnetic latitude). This location is that of the Murchison Widefield Array (MWA), a new low radio frequency array (80 to 300 MHz) being built with the objective of developing powerful new capabilities for radio astronomy, solar, heliospheric, and ionospheric science. The MWA is a radio interferometer that images large fields of view with unprecedented fidelity and dynamic range at these frequencies. With respect to the ionosphere, it will be able to make important new measurements of ionospheric scintillation and improve our understanding of midlatitude space weather events in the Southern Hemisphere. For example, by studying midlatitude space weather events in the Australian sector, the seasonal and geomagnetic dependencies of storm enhanced density (SED) can be characterized and separated from other forces that may impact its formation elsewhere, such as in the longitudinal sector of the South Atlantic Anomaly (SAA). After full commissioning, the MWA will consist of 2048 dipole antennas arranged as 128 “tiles,” each being a 4 × 4 array of dual-polarization dipoles. Currently, an engineering prototype comprising 32 tiles has been installed and has been used to observe the Faraday rotation from a linearly polarized satellite beacon on the DMSP-15 satellite. We will report on these initial observations of ionospheric Faraday rotation and on results from GPS receivers located at the site and elsewhere in the Australian continent. We will also discuss future space weather products enabled by the MWA.

We introduce the Fast Holographic Deconvolution method for analyzing interferometric radio data. Our new method is an extension of A-projection/software-holography/forward modeling analysis techniques and shares their precision deconvolution and wide-field polarimetry, while being significantly faster than current implementations that use full direction-dependent antenna gains. Using data from the MWA 32 antenna prototype, we demonstrate the effectiveness and precision of our new algorithm. Fast Holographic Deconvolution may be particularly important for upcoming 21 cm cosmology observations of the Epoch of Reionization and Dark Energy where foreground subtraction is intimately related to the precision of the data reduction., National Science Foundation (U.S.) (Grant AST CAREER-0847753), National Science Foundation (U.S.) (Grant AST-1003314), National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant AST-1008353), National Science Foundation (U.S.) (Grant AST-0908884), National Science Foundation (U.S.) (Grant PHY-0835713), Australian Research Council (Grant LE0775621), Australian Research Council (Grant LE0882938), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), MIT School of Science

A new generation of low-frequency radio telescopes is seeking to observe the redshifted 21 cm signal from the epoch of reionization (EoR), requiring innovative methods of calibration and imaging to overcome the difficulties of wide-field low-frequency radio interferometry. Precise calibration will be required to separate the expected small EoR signal from the strong foreground emission at the frequencies of interest between 80 and 300 MHz. The Moon may be useful as a calibration source for detection of the EoR signature, as it should have a smooth and predictable thermal spectrum across the frequency band of interest. Initial observations of the Moon with the Murchison Widefield Array 32 tile prototype show that the Moon does exhibit a similar trend to that expected for a cool thermally emitting body in the observed frequency range, but that the spectrum is corrupted by reflected radio emission from Earth. In particular, there is an abrupt increase in the observed flux density of the Moon within the internationally recognized frequency modulated (FM) radio band. The observations have implications for future low-frequency surveys and EoR detection experiments that will need to take this reflected emission from the Moon into account. The results also allow us to estimate the equivalent isotropic power emitted by the Earth in the FM band and to determine how bright the Earth might appear at meter wavelengths to an observer beyond our own solar system., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant AST-0908884), National Science Foundation (U.S.) (Grant PHY-0835713), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science

The Murchison Widefield Array (MWA) is a new low-frequency, wide-field-of-view radio interferometer under development at the Murchison Radio-astronomy Observatory in Western Australia. We have used a 32 element MWA prototype interferometer (MWA-32T) to observe two 50° diameter fields in the southern sky, covering a total of ~2700 deg[superscript 2], in order to evaluate the performance of the MWA-32T, to develop techniques for epoch of reionization experiments, and to make measurements of astronomical foregrounds. We developed a calibration and imaging pipeline for the MWA-32T, and used it to produce ~15' angular resolution maps of the two fields in the 110-200 MHz band. We perform a blind source extraction using these confusion-limited images, and detect 655 sources at high significance with an additional 871 lower significance source candidates. We compare these sources with existing low-frequency radio surveys in order to assess the MWA-32T system performance, wide-field analysis algorithms, and catalog quality. Our source catalog is found to agree well with existing low-frequency surveys in these regions of the sky and with statistical distributions of point sources derived from Northern Hemisphere surveys; it represents one of the deepest surveys to date of this sky field in the 110-200 MHz band., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant AST-0821321), National Science Foundation (U.S.) (Grant AST-0908884), National Science Foundation (U.S.) (Grant AST-1008353), National Science Foundation (U.S.) (Grant PHY-0835713), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), MIT School of Science, Smithsonian Astrophysical Observatory, Massachusetts Institute of Technology (Marble Astrophysics Fund), Raman Research Institute

The Murchison Wide-Field Array (MWA) is a low-frequency radio telescope, currently under construction, intended to search for the spectral signature of the epoch of reionization (EOR) and to probe the structure of the solar corona. Sited in western Australia, the full MWA will comprise 8192 dipoles grouped into 512 tiles and will be capable of imaging the sky south of 40° declination, from 80 MHz to 300 MHz with an instantaneous field of view that is tens of degrees wide and a resolution of a few arcminutes. A 32 station prototype of the MWA has been recently commissioned and a set of observations has been taken that exercise the whole acquisition and processing pipeline. We present Stokes I, Q, and U images from two ~4 hr integrations of a field 20° wide centered on Pictoris A. These images demonstrate the capacity and stability of a real-time calibration and imaging technique employing the weighted addition of warped snapshots to counter extreme wide-field imaging distortions., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), Australian Research Council (Grant LE0775621), Australian Research Council (Grant LE0882938), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), MIT School of Science

The Murchison Widefield Array (MWA) is a dipole-based aperture array synthesis telescope designed to operate in the 80-300 MHz frequency range. It is capable of a wide range of science investigations, but is initially focused on three key science projects. These are detection and characterization of 3-dimensional brightness temperature fluctuations in the 21cm line of neutral hydrogen during the Epoch of Reionization (EoR) at redshifts from 6 to 10, solar imaging and remote sensing of the inner heliosphere via propagation effects on signals from distant background sources,and high-sensitivity exploration of the variable radio sky. The array design features 8192 dual-polarization broad-band active dipoles, arranged into 512 tiles comprising 16 dipoles each. The tiles are quasi-randomly distributed over an aperture 1.5km in diameter, with a small number of outliers extending to 3km. All tile-tile baselines are correlated in custom FPGA-based hardware, yielding a Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point spread function (PSF) quality. The correlated data are calibrated in real time using novel position-dependent self-calibration algorithms. The array is located in the Murchison region of outback Western Australia. This region is characterized by extremely low population density and a superbly radio-quiet environment,allowing full exploitation of the instrumental capabilities., 9 pages, 5 figures, 1 table. Accepted for publication in Proceedings of the IEEE

We report on the detection of giant pulses from the Crab Nebula pulsar at a frequency of 200 MHz using the field deployment system designed for the Mileura Widefield Array's Low Frequency Demonstrator (MWA-LFD). Our observations are among the first high-quality detections at such low frequencies. The measured pulse shapes are deconvolved for interstellar pulse broadening, yielding a pulse-broadening time of 670$\pm$100 $\mu$s, and the implied strength of scattering (scattering measure) is the lowest that is estimated towards the Crab nebula from observations made so far. The sensitivity of the system is largely dictated by the sky background, and our simple equipment is capable of detecting pulses that are brighter than $\sim$9 kJy in amplitude. The brightest giant pulse detected in our data has a peak amplitude of $\sim$50 kJy, and the implied brightness temperature is $10^{31.6}$ K. We discuss the giant pulse detection prospects with the full MWA-LFD system. With a sensitivity over two orders of magnitude larger than the prototype equipment, the full system will be capable of detecting such bright giant pulses out to a wide range of Galactic distances; from $\sim$8 to $\sim$30 kpc depending on the frequency. The MWA-LFD will thus be a highly promising instrument for the studies of giant pulses and other fast radio transients at low frequencies., Comment: 10 pages, 6 figures, Accepted for publication in the Astrophysical Journal

In this paper, we explore for the first time the relative magnitudes of three fundamental sources of uncertainty, namely, foreground contamination, thermal noise, and sample variance, in detecting the H I power spectrum from the epoch of reionization (EoR). We derive limits on the sensitivity of a Fourier synthesis telescope to detect EoR based on its array configuration and a statistical representation of images made by the instrument. We use the Murchison Widefield Array (MWA) configuration for our studies. Using a unified framework for estimating signal and noise components in the H I power spectrum, we derive an expression for and estimate the contamination from extragalactic point-like sources in three-dimensional k-space. Sensitivity for EoR H I power spectrum detection is estimated for different observing modes with MWA. With 1000 hr of observing on a single field using the 128 tile MWA, EoR detection is feasible (S/N >1 for k [< over ~] 0.8 Mpc[superscript –1]). Bandpass shaping and refinements to the EoR window are found to be effective in containing foreground contamination, which makes the instrument tolerant to imaging errors. We find that for a given observing time, observing many independent fields of view does not offer an advantage over a single field observation when thermal noise dominates over other uncertainties in the derived power spectrum., National Science Foundation (U.S.) (Grant AST-0457585), National Science Foundation (U.S.) (Grant PHY-0835713), National Science Foundation (U.S.) (Grant CAREER-0847753), National Science Foundation (U.S.) (Grant AST-0908884), United States. Air Force Office of Scientific Research (Grant FA9550-0510247), Smithsonian Astrophysical Observatory, MIT School of Science

We present a Stokes I, Q and U survey at 189 MHz with the Murchison Widefield Array 32-element prototype covering 2400 square degrees. The survey has a 15.6 arcmin angular resolution and achieves a noise level of 15 mJy/beam. We demonstrate a novel interferometric data analysis that involves calibration of drift scan data, integration through the co-addition of warped snapshot images and deconvolution of the point spread function through forward modeling. We present a point source catalogue down to a flux limit of 4 Jy. We detect polarization from only one of the sources, PMN J0351-2744, at a level of 1.8 \pm 0.4%, whereas the remaining sources have a polarization fraction below 2%. Compared to a reported average value of 7% at 1.4 GHz, the polarization fraction of compact sources significantly decreases at low frequencies. We find a wealth of diffuse polarized emission across a large area of the survey with a maximum peak of ~13 K, primarily with positive rotation measure values smaller than +10 rad/m^2. The small values observed indicate that the emission is likely to have a local origin (closer than a few hundred parsecs). There is a large sky area at 2^h30^m where the diffuse polarized emission rms is fainter than 1 K. Within this area of low Galactic polarization we characterize the foreground properties in a cold sky patch at $(\alpha,\delta) = (4^h,-27^\circ.6)$ in terms of three dimensional power spectra

We present the first spectroscopic images of solar radio transients from the prototype for the Murchison Widefield Array (MWA), observed on 2010 March 27. Our observations span the instantaneous frequency band 170.9-201.6 MHz. Though our observing period is characterized as a period of `low' to `medium' activity, one broadband emission feature and numerous short-lived, narrowband, non-thermal emission features are evident. Our data represent a significant advance in low radio frequency solar imaging, enabling us to follow the spatial, spectral, and temporal evolution of events simultaneously and in unprecedented detail. The rich variety of features seen here reaffirms the coronal diagnostic capability of low radio frequency emission and provides an early glimpse of the nature of radio observations that will become available as the next generation of low frequency radio interferometers come on-line over the next few years., Comment: 15 pages, 5 figures, accepted for publication in Astrophysical Journal Letters. Movies for figures 4 and 5 available at http://www.mwatelescope.org/info/mwa_proto.html