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In this paper, we describe our efforts towards the development of a real-time radio imaging correlator for the Long-Wavelength Array station in Sevilleta, New Mexico. We briefly discuss the direct-imaging algorithm and present the architecture of the GPU implementation. We describe the code-level modifications carried out for one of the modules in the algorithm that improves GPU-memory management and highlight the performance improvements achieved through it. We emphasize our ongoing efforts in tuning the overall run-time duration of the correlator which in turn is expected to increase the operating bandwidth in order to address the demands of wide-band capability for radio transient science.

The External Calibrator for Hydrogen Observatories (ECHO) is an ongoing project to develop precision calibration sources for wide-field, low frequency, radio arrays such as the Murchison Widefield Array and the Hydrogen Epoch of Reionization Array which target 21cm radiation from primordial times. The accuracy of existing antenna beam models have been found to be a key factor limiting the realized sensitivity of the analysis pipelines. The precision required motivates us to go beyond applying a single model to each antenna in the array characterization and instead measure the response of the as-built system. We have developed a system for mapping the response pattern with a drone-mounted transmitter. Here we report a first series of tests, including our first test maps of known calibration standards and a second test mapping an MWA tile.

We have modelled the effect of ionic motion in MAPbI 3 cells, deepening the uuderstanding of how these mobile species can result in current-voltage hysteresis. In addition, we present a quantitative model for photo-deactivation of carrier traps to explain the observed increase in photoluminesence efficiency upon light-soaking.

The Hydrogen Epoch of Reionization Array (HERA), currently under construction, is a staged project that uses the unique properties of the 21-cm line from neutral hydrogen to probe the Epoch of Reionization (EoR) and the preceding Dark Ages. During these epochs, roughly 0.3 – 1 Gyr after the Big Bang, the first stars and black holes heat and reionize the Universe following cosmic recombination. Direct observation of the large scale structure of reionization and its evolution with time will have a profound impact on our understanding of the birth of the first galaxies and black holes, their influence on the intergalactic medium (IGM), and cosmology.

Significant effort has recently been turned to the problem of detecting and characterizing intergalactic hydrogen prior to its complete ionization by stars, occurring sometime before t=950Ma (z=6). The distribution of HI, visible in redshifted 21cm radio emission, is one of the few observables into the onset of non-linear structure leading to the birth of the first stars and galaxies. Before it was ionized by stellar UV radiation, HI was found throughout the universe, roughly tracing out the underlying matter distribution and temperature. HI 21cm emission from this epoch (6 < z < 12) is redshifted into the VHF radio band (100 < f < 200 MHz) and with a observer frequency depending on redshift/distance provides a fully three dimensional view. The emission is expected to have surface brightness of ∼25mK with a non-gaussian distribution and most power occurring on scales of 10cMpc.

Polarized foregrounds pose a threat for attempts to measure the 21cm Epoch of Reionization (EoR) power spectrum. Faraday rotation of natively polarized synchrotron emission modulates the phase of the polarization states Q and U by a factor of exp{−2iRMλ2}, where λ is the wavelength of incident light, and RM is a function of the magnetic field and electron density along the line of sight. This phase-factor is non-orthogonal to the frequency sine waves composing the EoR power spectrum, creating a potential leakage from polarized emission into the power spectrum. My recent paper, Moore, et al. 2013, exposes this as a problem, and presents a simulation estimating its severity.

The Precision Array for Probing the Epoch of Reionization (PAPER) is a focused experiment aimed at detecting the spatial power spectrum of neutral hydrogen emission during the Epoch of Reionization (EoR). PAPER is an interferometer operating from 100 – 200 MHz at the site of the future Square Kilometre Array (SKA) site in South Africa. The PAPER antennas measure linear polarization and the correlator produces full-Stokes output. PAPER currently has 64 antennas and has just completed a 141-day science integration. An expansion to 128 antennas and another long observing campaign will be complete in late 2013.

Recent interest in high redshift cosmology observations with the redshifted 21cm line has rekindled exploration of the VHF radio band (50–200MHz) for radio astronomy. Single antenna instruments like the ground-based EDGES and the proposed lunar orbiting DARE have the goal of characterizing the global HI signal and extracting astrophysical and cosmological information. One limitation over much of the band is strong man-made and naturally occurring interference, which DARE avoids by observing as it orbits the far side of the moon. Another advantage of space-based observing is avoidance of the ionosphere which becomes increasingly reflective at the lower end of the VHF band. Technical challenges to this type of mission include development of lower power wide-band spectrometers, better mapping of Earth originating interference, and incorporation of lessons learned from ongoing ground-based experiments. One of the main challenges faced by EDGES, observing the narrower but clean stretch of bandwidth found in Western Australia, is calibrating the spectral response of the antenna at the required 0.01dB level.

The Precision Array for Probing the Epoch of Reionization (PAPER) is a focused experiment aimed at detecting the spatial power spectrum of neutral hydrogen emission during the Epoch of Reionization (EoR). PAPER is an interferometer operating from 100 – 200 MHz, with antennas measuring linear polarization and a correlator producing full-Stokes output. The science array is located at the site of the future Square Kilometre Array (SKA) site in South Africa, with a prototyping and test facility in Green Bank, WV. A staged build-out of PAPER South Africa (PSA) began in late 2009. PAPER has been obtaining science-grade observations since late 2011, when 32 dipoles (PSA-32) began taking data full-Stokes data. PAPER currently has 64 antennas and has just completed a 141-day science integration (PSA-64). An expansion to 128 antennas and another long observing campaign will be complete in late 2013.

The Hydrogen Epoch of Reionization Arrays (HERA) roadmap is a staged program that uses the unique properties of the 21-cm line from neutral hydrogen to probe the Epoch of Reionization (EoR) and the preceding Dark Ages. During these epochs, roughly 0.31 Gyr after the Big Bang, the first stars and black holes heat and reionize the Universe following cosmic recombination. Direct observation of the large scale structure of reionization and its evolution with time will have a profound impact on our understanding of the birth of the first galaxies and black holes, their influence on the intergalactic medium (IGM), and cosmology.