Eye on the Sky: Convolving a Simulated Polarized Beam Pattern with Galactic Hydrogen 21-cm Spectral Cubes

Sean Heakes

A radio telescope’s beam pattern affects how it observes the sky, and can convert incoming unpolarized radiation into an instrumentally generated polarized response. This can, for example, create a fake circularly polarized signal that has the same pattern as the Zeeman effect in the 21-cm line. To better understand this, the Radio Telescope Modeling (RTMod) team at DRAO has developed simulated polarized beam patterns for the 26-meter John A. Galt (JAG) radio telescope. I will present the development of a Python-based pipeline for projecting the JAG’s beam onto the sky and convolving the beam with 21-cm spectral data cubes like the Effelsberg-Bonn HI Survey (EBHIS) and the HI4PI survey. The pipeline will be used to provide insight into how the beam influences the JAG’s polarized instrumental response.

Fabrication of multi-piece composite reflector panels for radio telescope applications: a novel technique

Longyu Li

This project demonstrates the feasibility of using multi-piece panels in telescope construction by designing, manufacturing and metrology verification of the sample panels. The designed panel consists of a front reflector skin, a backing skin, and cone supports either integrated into the back skin or separately connecting between the layers. Finite Element Analysis (FEA) was used to optimized the supporting pattern to limit gravitational deflection to 10 microns with minimal number of cones. Components were fabricated using vacuum infusion, with carbon molds and rubber-assisted carbon mold. One of the challenges here is to assemble the reflector panels to the backing pieces. Initially, a vacuum table with the reflector shape was built to assemble the backing skin to the reflector skin. During laser tracker metrology we have obtained that due to the post cure operation of the vacuum table, the shape is warped and that is transferred to the part. We have compared two gravity cases: 0 degree (bird bath) and the 45 degree. We have found that the RMS error distortion is very consisted and within 5 micron. This guarantees that the backup structure supports the reflector very well. It is also observed that the post curing of the resin makes the assembled part makes the surface deviation quite worse (factor of 2). In future, we will assemble the post cured parts on the mould to attain an improved part (close to the mould shape).

Large N, Small D – New Wave Radio Astronomy with CHORD

Matt Dobbs

Maple syrup, the Canadarm, hockey–and large N small d–all recognized internationally as enigmatic of Canada. CHIME and CHORD stand out as cutting-edge examples of large-number (N), small-diameter (D) radio telescope interferometers: breaking new ground in technology and revealing the cosmos with an unprecedented view. I’ll place these projects in the international context, show flashy (pun intended) results from CHIME, and describe the incredible potential for CHORD. The presentation will focus on science, people and technology – the three key ingredients behind success for projects of this type.

Gas Rich Galaxies and Cosmology

Kristine Spekkens

The HI content of nearby galaxies provides important insight into how they form and evolve within the standard cosmology. In this talk, I will highlight some of my group’s recent efforts to build statistical samples of HI detections for nearby galaxies to use as cosmological probes. I will first focus on how sensitive single-dish observations of dwarf satellite and ultra-diffuse galaxies are a powerful tool for measuring their structure and constraining formation models. I will then describe how the widefield WALLABY survey on ASKAP is delivering the first spatially-resolved populations of HI disks for comparison with cosmological predictions. This work paves the way for probing HI disks across cosmic time using the SKA when it comes online towards the end of this decade.

Gas Rich Galaxies and Cosmology: Paving the Way to the SKA

Kristine Spekkens

The atomic gas (HI) content of nearby galaxies provides important insight into how they form and evolve within the standard cosmology, which describes the structure and evolution of the universe itself. In this talk, I will highlight some of my group’s recent efforts to build statistical samples of HI disks to use as cosmological probes. I will first describe ongoing tensions between the structure of disk galaxies inferred from their rotation curves and predictions from cosmological simulations of galaxy assembly. I will then describe how the WALLABY widefield HI survey, now underway on the Australian SKA Pathfinder (ASKAP) will deliver population statistics to address these issues, and our progress on that front so far. This work paves the way for probing HI disks across cosmic time using the SKA telescope — an international mega-science project in which Canada is now a member — when it comes online towards the end of this decade.

The role of pulsar timing arrays for the detection of ultra long period GWs

Andrea Possenti

The rotational stability of a subset of the “recycled” pulsars allows us to use them as components of a galactic scale gravitational wave detector, dubbed Pulsar Timing Array (PTA), in turn providing an instrument to search for gravitational waves (GWs) in the ultra-long period range, thus complementing the capabilities of other current or future GW detectors. The various PTA experiments are producing very promising results, manifesting the first evidences for a detection, yet to be supported by additional data and analysis. The colloquium will describe the underlying ideas, the status, and the perspectives of these experiments, with a particular attention devoted to the European contribution, emerging from two decades long efforts of the European Pulsar Timing Array (EPTA) team.

Roadmap for the compendium of supermassive black hole images

Venkatessh Ramakrishnan

Following the transformational science enabled by the Event Horizon Telescope, we now focus on expanding the parameter space in terms of mass, spin and the role of magnetic field in extreme gravitational environment. It is thus imperative that imaging the silhouette of several black holes, beyond SgrA* and M87*, will provide vital constraints that will also probe the nature of (non-) General Relativity on a cosmological scale. I will present the ongoing preparations from a multiwavelength perspective for observations to be soon conducted with the EHT to image the photon rings and accretion flows of more AGNs in the nearby Universe. The structure of accretion flows will be driven fundamentally by their efficiency which will impact the opacity of the photon ring at the resolution set by the EHT. I will also show how the next generation EHT observations both from ground and space can be fundamental in this endeavour.

Probing Galactic and extragalactic magnetism with dense RM grids

Shannon Vanderwoude

Faraday rotation measures (RMs) are an invaluable tool for studying magnetic fields throughout the Universe. Current polarization surveys like the Polarisation Sky Survey of the Universe’s Magnetism (POSSUM) will increase the average RM sky density in large areas of the sky by a factor of ~30. Dense grids of extragalactic RMs be used to probe both Galactic and extragalactic magnetic fields. I will discuss the challenges associated with constructing increasingly dense RM grids and present prototype RM grids from two POSSUM pilot surveys. I will then outline two ongoing projects. The first project aims to use RM grids to probe the 3D Galactic magnetic field in the environment around the supernova remnant SN1006. The second project tests for correlation between polarization properties of bent radio galaxies in clusters and their degree of bending, contributing to our understanding of this population of sources in RM grids.

Radio Frequency Interference Management in Radio Astronomy

Braam Otto

This talk reflects on a personal journey spanning more than a decade in managing radio frequency interference in radio astronomy environments. Key RFI functions in an RFI Management System are presented, while highlighting the control of external (spectrum management) and internal (RFI management) sources of interference. We explore the development of an Observatory RFI/EMC Standard based on observation requirements, as well as the metrology techniques and measurement facilities required to qualify telescope and ancillary hardware to these stringent threshold levels.

Microwave Remote Sensing at the University of Bern

Axel Murk

The talk will give a brief overview of the passive microwave radiometers developed at the University of Bern for remote sensing of the atmosphere. Topics include the optical design using Physical Optics software, development of blackbody calibration targets for ground-based and spaceborne radiometers, high resolution digital FFT spectrometers and polarimetric calibration.

Weather radar monitoring and calibration using the radio noise coming from the Sun

Urs Germann

Proper adjustment of the antenna pointing and calibration is of crucial importance for weather radar performance. For such purposes, one of the best reference is the Sun. At the moment, accurate measurements of solar spectral irradiance exist thanks to the National Research Council of Canada (DRAO). Three measurements per day are available; the spectral band used is S-band (10.7 cm wavelength). The data set goes back to 1947: hence, it is precious, unique and with a great historical value. Since the solar radio output varies considerably in frequency and time, it would be beneficial to set up at European time and locations redundant accurate measurements of solar emissions in the same C-band (5.5 cm wavelength) of European national weather radar networks. For the next generation of Swiss weather radars we wish to set up one (or two) Sun measurement site(s) based on two identical radio telescopes that will run in parallel and act in a redundant way. They will operate at C-band, but also perform measurements in the crucial S-band part of the electromagnetic spectrum. We will briefly show the importance of calibration for automatic alerts based on the Swiss weather radar network.

Precision Polarimetry with the Jansky Very Large Array

Rick Perley (NRAO)

Accurate polarimetry using circularly-polarized feeds requires observation of at least one polarized calibrator with known electric vector position angle (EVPA). The only sources whose EVPAs are known with absolute certainty are thermal bodies — the Moon, Mars, and Venus (at frequencies below ~8 GHz). Using VLA observations of these objects, we have determined that the EVPAs of the standard calibrator 3C286 (J1331+3030) at frequencies above 1 GHz to be significantly lower than the 33 degrees which has been in use for decades.

Below ~2 GHz, an additional complicating factor becomes important — the Faraday rotation of the Earth’s ionosphere. Using six separate observations of the Moon, taken with the JVLA with its P-band receivers (295 — 450 MHz), we have determined that the global IONEX models significantly overestimate the ionospheric rotation measure, while the local-based ALBUS software model correctly estimates the ionospheric rotation with an accuracy better than 0.1 rad/m^2 — equivalent to <5 degrees at a frequency of 300 MHz. As a byproduct of this work, we have determined the intrinsic polarization properties of three polarized calibrators — DA240, 3C345, and 3C303.

Properties of Supernova Remnants from 1-D Models

Denis Leahy (University of Calgary)

Supernova remnants are the interaction of a supernova explosion with the interstellar medium, and result in spectacular radio and X-ray images. Here is described how 1-dimensional models (from simple to complex) can be used to learn about the physical properties of supernova remnants, such as their ages and explosion energies. Separately is described recent work on the significant effects of a simple (incorrect) assumption of the most common X-ray spectrum fitting software (XSPEC) and how to correct for this assumption to obtain physical values inferred from the X-ray spectrum.

Latest results of LOFAR’s Epoch of Reionization Key Science Project

Carolin Höfer (University of Groningen)

The Low Frequency Observing Array (LOFAR) is European’s largest radio interferometer operating between 30 – 240 MHz and a pathfinder for the SKA. Utilising a phased-array design, the antennae are grouped together into stations, with a dense core located near Exoloo, the northeast of The Netherlands. The Epoch of Reionization Key Science project uses the high-band antenna system, which covers LOFAR’s spectral response between 110-240 MHz corresponding to a redshift range z ~ 6 – 10. Its science goal is to answer how the first stars, galaxies and black holes formed by measuring the spatial fluctuations of the redshifted 21-cm emission of neutral hydrogen.

One of greatest challenges is to calibrate the instrument precisely, considering that astrophysical foregrounds are several orders brighter than the cosmological signal. I will discuss LOFAR’s latest data processing of the NCP and present our current upper limits on the 21-cm power spectrum. I will then discuss in more detail our current calibration strategy and some of the challenges we are still facing. I implemented a simulation pipeline and will show the effects of incomplete sky models on calibration solutions, images and power spectra.