Limits on the ultra-bright Fast Radio Burst population from the CHIME Pathfinder

We present results from a new incoherent-beam Fast Radio Burst (FRB) search on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder. Its large instantaneous field of view (FoV) and relative thermal insensitivity allow us to probe the ultra-bright tail of the FRB distribution, and to test a recent claim that this distribution's slope, $\alpha\equiv-\frac{\partial \log N}{\partial \log S}$, is quite small. A 256-input incoherent beamformer was deployed on the CHIME Pathfinder for this purpose. If the FRB distribution were described by a single power-law with $\alpha=0.7$, we would expect an FRB detection every few days, making this the fastest survey on sky at present. We collected 1268 hours of data, amounting to one of the largest exposures of any FRB survey, with over 2.4\,$\times$\,10$^5$\,deg$^2$\,hrs. Having seen no bursts, we have constrained the rate of extremely bright events to $<\!13$\,sky$^{-1}$\,day$^{-1}$ above $\sim$\,220$\sqrt{(\tau/\rm ms)}$ Jy\,ms for $\tau$ between 1.3 and 100\,ms, at 400--800\,MHz. The non-detection also allows us to rule out $\alpha\lesssim0.9$ with 95$\%$ confidence, after marginalizing over uncertainties in the GBT rate at 700--900\,MHz, though we show that for a cosmological population and a large dynamic range in flux density, $\alpha$ is brightness-dependent. Since FRBs now extend to large enough distances that non-Euclidean effects are significant, there is still expected to be a dearth of faint events and relative excess of bright events. Nevertheless we have constrained the allowed number of ultra-intense FRBs. While this does not have significant implications for deeper, large-FoV surveys like full CHIME and APERTIF, it does have important consequences for other wide-field, small dish experiments

Calibration and testing components of the Canadian Hydrogen Intensity Mapping Experiment

This thesis details three projects for the Canadian Hydrogen Intensity Mapping Project (CHIME). The first was the implementation of a new algorithm for setting the gains of the Field Programmable Gate Arrays (FPGAs). This algorithm handles radio interference from sources such as TV stations more effectively than its predecessor. It was developed, tested, and incorporated into the prototype CHIME data collection pipeline. The second was the characterization of the Analog to Digital Converter (ADC) boards, to check that the specifications set out by the ADC chip manufacturer were met and that the boards behaved as expected. The boards performed as expected and that they were therefore suitable for use in CHIME.Third, investigating the use of satellites as a calibration source, which, if possible, would be complementary to the current calibration approaches. Satellites were successfully detected and provided information about the CHIME beam that was not available from other sources.Cette thèse décrit trois projets réalisés pour le telescope CHIME (Canadian Hydrogen Intensity Mapping Experiment).Premièrement, nous présentons un nouvel algorithme pour l'ajustement des gains appliqués sur les spectres des signaux calculés par le l'électronique d'acquisition de CHIME. Cet algorithme gère mieux que ses prédécesseurs les effets des interférences radio causées par les sources telles que les station de télévision. Cet algorithme a été développé, testé, et inclus dans la pipeline d'acquisition de données du prototype de CHIME. Deuxièmement, nous avons caractérisé les cartes de conversion analogique-numériques de CHIME et avons confirmé que les convertisseurs rencontraient les spécification du fabricant et que les circuits se comportait généralement selon les attentes et sont adéquates pour les objectifs du projet.Troisièmement, nous avons étudié l'utilisation de satellites comme source de calibration pouvant potentiellement complémenter les méthodes de calibration courantes. En utilisant le prototype de CHIME, nous avons réussi à détecter des signaux satellites qui nous ont permis de recueillir de l'information sur les patron de rayonnement des antennes de CHIME qui n'était pas disponibles à partir d'autres sources

The hydrogen epoch of reionization array dish III: measuring chromaticity of prototype element with reflectometry

Abstract Spectral structures due to the instrument response is the current limiting factor for the experiments attempting to detect the redshifted 21 cm signal from the Epoch of Reionization (EoR). Recent advances in the delay spectrum methodology for measuring the redshifted 21 cm EoR power spectrum brought new attention to the impact of an antenna’s frequency response on the viability of making this challenging measurement. The delay spectrum methodology provides a somewhat straightforward relationship between the time-domain response of an instrument that can be directly measured and the power spectrum modes accessible to a 21 cm EoR experiment. In this paper, we derive the explicit relationship between antenna reflection coefficient (S11) measurements made by a Vector Network Analyzer (VNA) and the extent of additional foreground contaminations in delay space. In the light of this mathematical framework, we examine the chromaticity of a prototype antenna element that will constitute the Hydrogen Epoch of Reionization Array (HERA) between 100 and 200 MHz. These reflectometry measurements exhibit additional structures relative to electromagnetic simulations, but we find that even without any further design improvement, such an antenna element will support measuring spatial k modes with line-of-sight components of k∥ > 0.2h Mpc− 1. We also find that when combined with the powerful inverse covariance weighting method used in optimal quadratic estimation of redshifted 21 cm power spectra the HERA prototype elements can successfully measure the power spectrum at spatial modes as low as k∥ > 0.1h Mpc− 1. This work represents a major step toward understanding the HERA antenna element and highlights a straightforward method for characterizing instrument response for future experiments designed to detect the 21 cm EoR power spectrum

The hydrogen epoch of reionization array dish III: measuring chromaticity of prototype element with reflectometry

Spectral structures due to the instrument response is the current limiting factor for the experiments attempting to detect the redshifted 21 cm signal from the Epoch of Reionization (EoR). Recent advances in the delay spectrum methodology for measuring the redshifted 21 cm EoR power spectrum brought new attention to the impact of an antenna’s frequency response on the viability of making this challenging measurement. The delay spectrum methodology provides a somewhat straightforward relationship between the time-domain response of an instrument that can be directly measured and the power spectrum modes accessible to a 21 cm EoR experiment. In this paper, we derive the explicit relationship between antenna reflection coefficient (S 11 ) measurements made by a Vector Network Analyzer (VNA) and the extent of additional foreground contaminations in delay space. In the light of this mathematical framework, we examine the chromaticity of a prototype antenna element that will constitute the Hydrogen Epoch of Reionization Array (HERA) between 100 and 200 MHz. These reflectometry measurements exhibit additional structures relative to electromagnetic simulations, but we find that even without any further design improvement, such an antenna element will support measuring spatial k modes with line-of-sight components of k ∥ > 0.2h Mpc − 1 . We also find that when combined with the powerful inverse covariance weighting method used in optimal quadratic estimation of redshifted 21 cm power spectra the HERA prototype elements can successfully measure the power spectrum at spatial modes as low as k ∥ > 0.1h Mpc − 1 . This work represents a major step toward understanding the HERA antenna element and highlights a straightforward method for characterizing instrument response for future experiments designed to detect the 21 cm EoR power spectrum