DRAO Seminar Series Fall 2016

Fast Radio Bursts

Paul Scholz (McGill)

A new phenomenon has emerged in time-domain astronomy in the past few years: the Fast Radio Burst. Fast Radio Bursts (FRBs) are millisecond-duration radio bursts whose dispersion measures imply that they originate from far outside of the Galaxy. Their origin is as yet unknown; their durations and energetics imply that they involve compact objects, such as neutron stars or black holes. Due to the extreme luminosities implied by their distances and the previous absence of any repeat burst in follow-up observations, many potential explanations for FRBs involve one-time cataclysmic events.

I will summarize the history of the field of FRB astronomy from the discovery of the first burst in 2007 to exciting recent developments in the past year. I will also provide a more detailed description of one of the recent developments: the discovery of a repeating FRB which, due to its repeating nature, cannot come from a cataclysmic event. Finally, I will review the future of FRB science and the unique contribution of the CHIME telescope at DRAO.

Bayesian Planet Searches for the 10 cm/s Radial Velocity Era

Phil Gregory (UBC)

Intrinsic stellar variability has become the main limiting factor for planet searches in both transit and radial velocity (RV) data. New spectrographs are under development like ESPRESSO and EXPRES that aim to improve RV precision by a factor of approximately 10 over the current best spectrographs. This will greatly exacerbate the challenge of distinguishing planetary signals from stellar activity induced RV signals.

At the same time good progress has been made in simulating stellar activity signals. Last year, Xavier Dumusque challenged the community to a large scale blind test using both simulated and real data to understand the limitations of present solutions and to select the best approach. For this competition I introduced a new Bayesian method based on Apodized Keplerian periodograms. My talk will focus on some of the statistical lesson learned from this challenge with an emphasis on Bayesian methodology.

The Low-Noise Receiver Systems Developed for the EVLA Project

Bob Hayward (NRAO)

The Very Large Array (VLA) is widely regarded as the world’s most scientifically productive radio telescope. Operated by the National Radio Astronomy Observatory (NRAO), this aperture synthesis interferometer consists of 27 movable antennas, each 25 meters in diameter, which can be configured to provide the resolution of an antenna whose size can range from 1 to 36 kilometers in width. When commissioned in 1980, the VLA could only observe celestial sources in four narrow frequency bands centered at 1.5, 4.7, 15 and 23 GHz. Over the next 20 years, its receiver systems were incrementally improved to give the Array better sensitivity and wider frequency coverage. But as the 21st century dawned, the VLA’s performance was still limited by its 1970’s era technology.

The recently completed Expanded Very Large Array (EVLA) project has provided many major enhancements, including the installation of 240 new, state-of-the-art, low-noise, cryogenic receivers that now enable astronomers to observe at any frequency between 1 and 50 GHz and with bandwidths as wide as 8 GHz, some 80 times broader than before. Over the 10 year long EVLA upgrade effort, the author was deeply involved in the design and testing of the prototype receiver hardware as well as the production of several of the new receiver bands. This talk will discuss the EVLA’s front-end systems and the innovative solutions developed by the various NRAO design teams to meet the demanding performance goals required for the project, including such critical microwave components as the broad-band feeds, circular polarizers, low-noise amplifiers and multifunction MMIC modules. The talk will also attempt to put the VLA into historical context by briefly describing the evolution of the VLA’s low-noise receiver system from its inception to the present day.

Magnetic Fields from the Milky Way to Large Redshifts

Phil Kronberg (Toronto)

I summarise attempts to probe interstellar, intracluster, and intergalactic magnetic fields. The story begins with the Galaxy disc and halo. It proceeds to supragalaxy scales, galaxy clusters, the IGM, and includes some newer magnetic field probes using very high-energy cosmic rays and gamma rays. I close by discussing a recent 3-D plot of redshift-dependent, stacked rotation measure distributions observed for extragalactic radio sources.

Real-Time Detection of an Extreme Scattering Event: New Constraints on Interstellar Plasma Lenses

Keith Bannister (CSIRO)

Extreme scattering events (ESEs) are distinctive fluctuations in the brightness of astronomical radio sources caused by occulting plasma lenses in the interstellar medium. The inferred plasma pressures of the lenses are roughly 1000 times the ambient pressure, challenging our understanding of gas conditions in the Milky Way. Using a new survey (ATESE) on the Australia Telescope Compact Array, we have discovered an ESE while it was in progress. We report radio and optical follow-up observations. Modelling of the radio data demonstrates that the lensing structure is a density enhancement and that the lens is diverging, ruling out one of two competing physical models. ATESE will uncover many more ESEs, addressing a long-standing mystery of the small-scale gas structure of the Galaxy. I will also discuss some other interesting variability found by ATESE.

The Five-Hundred-Meter Aperture Spherical Telescope

Tim Robishaw (DRAO)