Authors:Alexander Faustmann, Jacki Gilmore, Vereese van Tonder, Maciej Serylak Abstract: Journal of Astronomical Instrumentation, Volume 09, Issue 04, December 2020. A combination of the very low signal-to-noise ratio and the very large parameter space spanned by pulsar emissions makes pulsar detection a challenging task. Currently, brute force parameter searches are often used for pulsar detection and a cyclostationary Gaussian model is assumed for pulsar emissions. Higher-Order spectra offer high signal-to-noise ratio domains in problems where the desired signal is polluted by Gaussian noise. The presence of nonzero higher-order spectral components in pulsar bursts may offer alternative detection methods. This work presents a review of higher-order statistics and offers a motivation for their use in the characterization of pulsar bursts. A dish from the MeerKAT telescope was used to acquire recorded radio bursts from pulsar J0437-4715. These bursts were found to contain nonzero bispectral components that were dispersed in the same way as the components of the power spectrum. Citation: Journal of Astronomical Instrumentation PubDate: 2020-12-21T08:00:00Z DOI: 10.1142/S225117172050018X Issue No:Vol. 09, No. 04 (2020)

Authors:H. C. Chiang, T. Dyson, E. Egan, S. Eyono, N. Ghazi, J. Hickish, J. M. Jáuregui-Garcia, V. Manukha, T. Ménard, T. Moso, J. Peterson, L. Philip, J. L. Sievers, S. Tartakovsky Abstract: Journal of Astronomical Instrumentation, Volume 09, Issue 04, December 2020. Measurements of redshifted 21[math]cm emission of neutral hydrogen at [math][math]MHz have the potential to probe the cosmic “dark ages,” a period of the universe’s history that remains unobserved to date. Observations at these frequencies are exceptionally challenging because of bright Galactic foregrounds, ionospheric contamination, and terrestrial radio-frequency interference. Very few sky maps exist at [math][math]MHz, and most have modest resolution. We introduce the Array of Long Baseline Antennas for Taking Radio Observations from the Sub-Antarctic (ALBATROS), a new experiment that aims to image low-frequency Galactic emission with an order-of-magnitude improvement in resolution over existing data. The ALBATROS array will consist of antenna stations that operate autonomously, each recording baseband data that will be interferometrically combined offline. The array will be installed on Marion Island and will ultimately comprise 10 stations, with an operating frequency range of 1.2–125[math]MHz and maximum baseline lengths of [math][math]km. We present the ALBATROS instrument design and discuss pathfinder observations that were taken from Marion Island during 2018–2019. Citation: Journal of Astronomical Instrumentation PubDate: 2020-12-21T08:00:00Z DOI: 10.1142/S2251171720500191 Issue No:Vol. 09, No. 04 (2020)

Authors:Jean-Luc Margot Abstract: Journal of Astronomical Instrumentation, Ahead of Print. Most planetary radar applications require recording of complex voltages at sampling rates of up to 20[math]MHz. I describe the design and implementation of a sampling system that has been installed at the Arecibo Observatory, Goldstone Solar System Radar, and Green Bank Telescope. After many years of operation, these data-taking systems have enabled the acquisition of hundreds of datasets, many of which still await publication. Citation: Journal of Astronomical Instrumentation PubDate: 2020-12-21T08:00:00Z DOI: 10.1142/S225117172150001X

Authors:Benjamin D. Donovan, Randall L. McEntaffer, Casey T. DeRoo, James H. Tutt, Fabien Grisé, Chad M. Eichfeld, Oren Z. Gall, Vadim Burwitz, Gisela Hartner, Carlo Pelliciari, Marlis-Madeleine La Caria Abstract: Journal of Astronomical Instrumentation, Ahead of Print. The soft X-ray grating spectrometer on board the Off-plane Grating Rocket Experiment (OGRE) hopes to achieve the highest resolution soft X-ray spectrum of an astrophysical object when it is launched via suborbital rocket. Paramount to the success of the spectrometer are the performance of the [math] reflection gratings populating its reflection grating assembly. To test current grating fabrication capabilities, a grating prototype for the payload was fabricated via electron-beam lithography at The Pennsylvania State University’s Materials Research Institute and was subsequently tested for performance at Max Planck Institute for Extraterrestrial Physics’ PANTER X-ray Test Facility. Bayesian modeling of the resulting data via Markov chain Monte Carlo (MCMC) sampling indicated that the grating achieved the OGRE single-grating resolution requirement of [math] at the 94% confidence level. The resulting [math] posterior probability distribution suggests that this confidence level is likely a conservative estimate though, since only a finite [math] parameter space was sampled and the model could not constrain the upper bound of [math] to less than infinity. Raytrace simulations of the tested system found that the observed data can be reproduced with a grating performing at [math]. It is therefore postulated that the behavior of the obtained [math] posterior probability distribution can be explained by a finite measurement limit of the system and not a finite limit on [math]. Implications of these results and improvements to the test setup are discussed. Citation: Journal of Astronomical Instrumentation PubDate: 2020-11-27T08:00:00Z DOI: 10.1142/S2251171720500178

Authors:Peter Tokarsky, Alexander Konovalenko, Mykola Kalinichenko, Serge Yerin Abstract: Journal of Astronomical Instrumentation, Ahead of Print. This paper presents the technique of numerical estimation of ground parameters impact on the performances of an active antenna used as an element of a phased array antenna of a modern low-frequency radio telescope. Three ground conditions were considered, two of them wet and dry, which correspond to the extreme values of seasonal deviations of its parameters, as well as its median state (“normal ground”). The results of computer simulation are given for the active antenna of the GURT radio telescope with a ground screen in the form of a square wire grid of [math][math]m and without it. It is shown that the addition of the ground screen markedly reduces the influence of the ground conditions on some parameters of the antenna, in particular, the dipole impedance and radiation efficiency. At the same time, the ground screen does not protect the most important antenna parameters for radio astronomy, such as sensitivity and absorption area, from the impact of the ground conditions changes. Variations of these parameters for an active antenna with a screen remain approximately the same as without it. Citation: Journal of Astronomical Instrumentation PubDate: 2020-10-12T07:00:00Z DOI: 10.1142/S2251171720500154

Authors:C. R. Subrahmanya, O. S. Sarun, Yogindra Abhyankar, Sajish Chandrababu, Chinmay Bahulekar Abstract: Journal of Astronomical Instrumentation, Ahead of Print. Modern and upcoming radio telescopes at low frequencies are often characterized by hundreds or thousands of antenna elements operating at wide bandwidths up to about 0.5[math]GHz. A spectral correlator for such an array is required to estimate the cross-power spectrum of the response of each element with that of every other element with a high spectral resolution. The resulting all-to-all connectivity between signals from the entire array poses a serious bottleneck. In this paper, we propose a simple digital receiver architecture that interfaces the digitized time series from a large number of antenna elements to a High-Performance Computing (HPC) cluster through a communication switch to overcome the data ingest bottleneck. Each HPC node can then perform wideband processing in steps of finite but significant time-slices for the entire array. We explain in detail the implementation of our architecture for the proposed expansion of the Ooty Wide Field Array (OWFA) into a 1056 element array. Since the proposed digital receiver is based on Field Programmable Gate Array (FPGA), it can be reconfigured for different applications. This is illustrated by considering the case of Phased Array Feeds (PAF) for the proposed expanded Giant Metrewave Radio Telescope (eGMRT). Citation: Journal of Astronomical Instrumentation PubDate: 2020-10-07T07:00:00Z DOI: 10.1142/S2251171720500166