Departmental Doctoral Oral Examination (Thesis Title: “Timing Pulsars and Detecting Radio Transients with CHIME”)
Physics and Astronomy
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a transit telescope located at the Dominion Radio Astrophysical Observatory in Kaleden, BC. Though initially designed to map redshifted neutral hydrogen and constrain dark energy, it also supports several commensal science projects. This thesis focuses on work conducted with the CHIME/FRB fast radio burst searching backend and the CHIME/Pulsar pulsar timing backend.
This thesis focuses on pulsars and fast radio bursts. Pulsars are rapidly rotating, highly magnetized neutron stars, the remnants of massive stars following their supernova explosions. Fast Radio bursts are mysterious millisecond duration radio transients, originating from outside the Milky Way Galaxy. Although their origin is still unknown, evidence is mounting that FRBs also originate from neutron stars or other compact objects, much like pulsars.
First, we discuss ongoing efforts to integrate CHIME/Pulsar daily cadence pulsar timing data into large-scale pulsar timing datasets maintained by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav is engaged in a long-term effort to detect gravitational wave signals from supermassive black hole mergers via pulsar timing. The full NANOGrav array consists of approximately 70 sources; in this initial work, we present timing solutions from CHIME/Pulsar data for approximately 10 sources. Though CHIME/Pulsar is a less sensitive instrument than other NANOGrav telescopes like the Green Bank Telescope and the Arecibo Observatory, CHIME/Pulsar's lower frequency and daily observation cadence allow it to provide substantial statistical power to the NANOGrav dataset.
We then discuss new pulsars and rotating radio transients (RRATs) discovered via detection of single pulses by CHIME/FRB. Discovering new pulsars with single pulses is a new technique with the potential to revolutionize our understanding of previously difficult to detect sources. Conventional pulsar searches look at small patches of sky for short periods of time; in contrast, CHIME/FRB views the entire Northern sky each day. CHIME/FRB is thus ideally situated to detect sources with substantial periods of intermittency or high levels of transience. CHIME/Pulsar's ability to track sources digitally allows us to follow-up initial detections with more conventional search mode observations. The combined effect has allowed us to discover and characterize seven new sources so far.
Finally, we discuss observations conducted with the Arecibo Observatory's 300-m single dish radio telescope, following-up low declination FRBs discovered with CHIME/FRB. This work focused on better understanding repeating FRBs by observing a small number of known repeaters in depth, as well as a moderate number of observations of non-repeating FRBs with a downward-drifting time-frequency structure commonly associated with repeating FRBs. This work did not result in the detection of new bursts from these sources, but it allows us to put tighter constraints on the repetition rate of these sources and the possibility of a low-luminosity population of repeat bursts from known repeating FRBs.