Ingrid Stairs

Relevant Thesis-Based Degree Programs

Graduate Student Supervision

Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Searching for millisecond and slow pulsars with CHIME (2025)

Born in core-collapse supernovae, pulsars are highly-magnetized, spinning neutron stars, which emit highly directional electromagnetic radiation in beams above their magnetic poles. This produces a lighthouse effect: we see a pulse of radiation as the beam crosses our line-of-sight, repeating with each rotation of the neutron star.These periodic pulses can reveal a wealth of information about the neutron star, its environment, material the signal encounters on its way to Earth, and even the behaviour of spacetime. Many mysteries remain about these objects and, thus far, we have only discovered a small fraction of them. New surveys to discover more pulsars, therefore, have great scientific potential.In this thesis I use the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope to perform two distinct pulsar surveys on the same small patch of sky. These serve as pilots for larger-scale surveys over the entire CHIME-visible sky.The CHIME All-sky Multi-day Pulsar Stack Search (CHAMPSS) survey uses the data stream from the CHIME/FRB instrument, taking data from the whole Northern sky as it passes overhead and combining data from multiple days to detect fainter pulsars. However, it is not sensitive to the fastest pulsars with periods below ~10ms.The other survey uses the CHIME/Pulsar system to take multiple observations of the same point on the sky, correcting for different amounts of material between the Earth and potential pulsars. This scheme lets it detect the fastest pulsars further out into the Galaxy. However, the CHIME/Pulsar survey does not combine multiple days' data and so will not detect the faintest pulsars found by CHAMPSS.The two surveys are thus sensitive to different, but overlapping, sections of the pulsar population, and further demonstrate the collaborative nature of CHIME which allows multiple experiments to run simultaneously.In this thesis I describe the software pipeline for each survey. The CHAMPSS pipeline I developed as part of a group; the CHIME/Pulsar pipeline was an individual project. I also present PSR J2108+5001, a newly discovered pulsar in the pilot survey area, and J1629+4636, J2100+4711, J2151+5128, and J2319+4919 which were discovered during a subsequent CHAMPSS commissioning survey.

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A study of sporadic pulsars and radio transients with the CHIME telescope (2024)

The Canadian Hydrogen Mapping Experiment (CHIME) is a radio telescope located in British Columbia, Canada. Initially built to survey the neutral hydrogen in the universe, it has had multiple additional jobs thrust upon its shoulders. One such responsibility is the discovery and continual monitoring of pulsars. With the large sky coverage and daily observing cadence, CHIME lends itself well to the hitherto poorly understood population of sporadic pulsars. The understanding of the population of sporadic pulsars, and in turn, all pulsars, will be informative for many areas of Galactic archaeology and supernova. First, I develop a new way to correct for the selection effects in the brightness distribution and nulling fraction of pulsars using their single pulses. This method, called LuNfit, is unique in that it can be applied to the most extreme examples of sporadic pulsars. Furthermore, it can be used on radio transients that do not have underlying periods, such as repeating fast radio bursts. I demonstrate the effectiveness of LuNfit by applying it to three known rotating radio transients (RRATs). I show that despite being classified as a RRAT through null detections when folding, PSR J0012+54 is may be a persistent emitter. Then, I take LuNfit further and incorporate pulse widths into the process. I conduct a year-long single pulse survey with CHIME/FRB, detecting 424 known and unknown pulsars. I apply LuNfit to a subset of 35 pulsars. This effort lays the groundwork for a larger population level analysis using large field of view single pulse surveys like CHIME/FRB. Finally, I discover a new long period transient, CHIME J0630+25, with a period of 421 s. This marks the fifth object in this new class. Their nature remains unknown, but I speculate that CHIME J0630+25 is likely a white dwarf or a neutron star. I further monitor the object across multiple wavelengths. With Neils Gehrels Swift X-ray telescope observations, I find 2 potential X-ray counterparts. At a distance of 170 pc, CHIME J0630+25 is the closest known long period transient.

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Timing pulsars and detecting radio transients with CHIME (2021)

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 highly magnetized neutron stars known as magnetars. 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 eight sources. These initial results are promising and suggest a bright future for CHIME/Pulsar-NANOGrav data combination.We then discuss new pulsars and rotating radio transients (RRATs) discovered via detection of single pulses by CHIME/FRB. CHIME/FRB is 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 repeater and some bursts with repeater-like structure in-dept. It did not result in the detection of new bursts from these sources, but it allows us to constrain the repetition rate of these sources.

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Mass and Geometric Measurements of Binary Radio Pulsars (2017)

One of the primary, long-term goals in high-energy astrophysics is the measurement of macroscopic parameters that constrain the equation of state for compact stellar objects. For neutron stars, known to be composed of the densest matter in the Universe, measurements of their masses and sizes are of considerable importance due to the poorly understood processes that govern their interiors. Measurements of relativistic “post-Keplerian” effects in binary systems can be used to significantly constrain viable equations of state, test modern theories of gravitation, verify binary-evolution models that predict correlations between certain binary parameters, and determine the Galactic neutron-star mass distribution that is expected to reflect different supernovae mechanisms and evolutionary paths. In this thesis, we use established pulsar-timing techniques to analyze signals from radio pulsars in 25 binary systems, as well as from one pulsar in a hierarchical triple system, in order to detect perturbations from Keplerian motion of the bodies. We characterize observed relativistic Shapiro timing delays to derive estimates of the component masses and inclination angles in 14 pulsar-binary systems, and measure a large number of secular variations due to kinematic, relativistic and/or third-body effects in the majority of binary systems studied here. We find a wide range of statistically-significant pulsar masses and make new detections of the relativistic Shapiro-delay signal in four binary systems for the first time. In the relativistic PSR B1534+12 binary system, we derive an accurate and precise rate of geodetic precession of the pulsar-spin axis -- due to secular variations of electromagnetic pulse structure -- that is consistent with the prediction from general relativity. In the PSR B1620-26 triple system, we discuss ongoing efforts to simultaneously model both “inner” and “outer” orbits and tentatively measure secular variations of all “inner-orbital” elements that we show are likely due to third-body interactions between the smaller orbit and outer companion, which can eventually be used to constrain orientation angles and possibly the pulsar mass in the near future.

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Radio Observations of Two Binary Pulsars (2012)

The study of pulsars in binary systems produces a wide variety of scientific results, including unique tests of general relativity and constraints on the equation of state of matter at extremely high densities. Through pulsar timing (which utilizes the fact that pulsars are precise clocks), it is possible to precisely measure the orbital parameters and masses of some binary pulsars, which can place constraints on their mass transfer histories. We present timing results for two binary pulsars.The intermediate-mass binary pulsar (IMBP) PSR J0621+1002 is a mildly recycled pulsar in an 8.3-day orbit around a massive white dwarf (WD) companion. It is one of only two known IMBPs with a precise mass measurement. We collected 9 days' worth of data using the 305-metre Arecibo telescope (allowing for full orbital coverage), which we used to improve constraints on the advance of periastron, and in turn, the pulsar and companion masses (to 1.53^{+0.10}_{-0.20}M☉ and 0.76^{+0.28}_{-0.07} solar masses, respectively) and inclination angle of the system. These results, combined with the relatively long orbital period, suggest a disk accretion evolutionary scenario involving short-lived periods of hyper-accretion, in which a moderate amount of mass has been transferred to the neutron star (NS).PSR J1906+0746 is a young pulsar in a compact ~4-hour orbit around a companion that was discovered in the early stages of the PALFA survey using the 305-metre Arecibo telescope. We present the timing results using data collected between 2005 to 2009 using the Green Bank, Arecibo, and Nançay telescopes. We have measured the advance of periastron, the time dilation and gravitational redshift parameter, and the orbital decay, and we find the pulsar and companion masses to be 1.323^{+0.011}_{-0.011}M☉ and 1.290^{+0.011}_{-0.011} solar masses, respectively. Although the companion may be a second NS, it is more likely to be a massive WD. The system's evolution probably involved a substantial transfer of mass from the WD progenitor onto the NS progenitor through Roche-lobe overflow accretion, followed by the formation of the WD, and a short common envelope phase, and finally the ejection of the envelope and the pulsar-forming supernova.

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Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

High cadence pulsar timing with CHIME/Pulsar (2025)

Pulsars are rapidly rotating, highly magnetized neutron stars—the collapsed remnants of massive stars following a supernova explosion. They produce beams of radiation that reach our observatories on Earth at regular intervals. The precise timing of these radio pulses has many applications, including exploring fundamental physics, testing the predictions of general relativity,probing the interstellar medium, and even detecting gravitational waves. This work investigates variability in pulsar emission using the unprecedented observing cadence of the CHIME telescope.The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a radio telescope near Penticton, British Columbia, Canada. Although initially conceived as a cosmology experiment, it has proven to be an excellent instrument for discovering and studying radio transients. This thesis utilizes the CHIME/Pulsar science backend.First, for PSR B0540+23 we conduct an analysis to explore emission modulation during periods of low solar elongation, which occur once a year. Each year, the pulsar is occulted by the solar wind due to its position in the sky. We observe dispersion measure variations caused by excess solar wind electrons along the line of sight and infer a solar electron density based on these observations.Next, we study nulling and mode-changing behavior in PSRs B0809+74 and B0329+54. We employ a matched filtering pipeline to identify this behavior. We investigate links between these phenomena and an excess of outlier TOAs identified by the NANOGrav Collaboration’s outlier analysis. We find that the outlier analysis is sensitive to mode-changing in PSR B0329+54.These findings highlight the utility of CHIME/Pulsar’s daily observing cadence for studying pulsar emission. With the capabilities of CHIME/Pulsar, we are able to identify yearly occultations of PSR B0540+23 by the solar wind. We also provide a foundation for applying the NANOGrav outlieranalysis to identify mode-changing in pulsars. The results of this work highlight the value of CHIME/Pulsar in studying a wide range of pulsar emission phenomena.

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Finding new pulsars using CHIME/FRB single pulse events (2021)

Pulsars are compact objects which are remnants of once-massive stars. Most are lighthouses in radio frequencies, and studying them has led to significant discoveries of exoplanets, gravitational waves, and fundamental physics theories. An ongoing research area is the source of pulsar emission and, in turn, the strange way telescopes see some pulsars. These include intermittent pulsars and Rotating Radio Transients (RRATs) i.e. ones that turn on for some time but remain quiet otherwise. While the study of pulsars stretches back to 1967, a more contemporary discovery is that of Fast Radio Bursts (FRBs). The discovery in 2007 led to a burgeoning field in radio astronomy, which has enticed many current-generation telescopes. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is among the bank of telescopes that have been commissioned to find FRBs. This thesis addresses the development and deployment of a novel pipeline for finding new pulsars from galactic and extragalactic single-pulse events. We employ the vast astronomical database collected by the aptly named the CHIME/FRB collaboration over 29 months. The majority of the work was to sort through the CHIME/FRB database for RFI and known pulsars before implementing an unsupervised machine learning algorithm, DBSCAN. DBSCAN made clusters of transient astronomical events which are checked against known pulsars in extant catalogs before being followed up by a second CHIME backend instrument, CHIME/Pulsar. The process has led to 144 candidates, with 12 confirmed new pulsars. Many of the pulsars discovered are RRATs, objects that are atypical for a pulsar in that the pulsed emission is sporadic and intermittent. The continued study of RRATs have the potential to elucidate their intermittency and, by extension, the emission mechanism for pulsars. Thus adding to the current ~120 known RRATs will enable pulsar astronomers to make more substantial claims regarding the estimated ~10⁵ RRATs in the Milky Way Galaxy.

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Applying convolutional neural networks to classify fast radio bursts detected by the CHIME telescope (2020)

Timing and analysis of eclipsing black widow pulsar PSR J2256-1024 (2018)

Pulsars are rapidly spinning neutron stars emitting radiation about their magnetic field axes. Misalignment of the spin and magnetic axes causes a “lighthouse” effect where we observe radiation pulses, in time with the pulsar’s rotation. Millisecond pulsars are those which have accreted material from a companion star, spinning themselves up to rotate faster. Some millisecond pulsars occur in tight orbits with low mass companions; this combination can lead to the companion losing material, due to bombardment by energetic particles from the pulsar, presumably eventually destroying the companion. These pulsars are known as Black Widows (BWs). This thesis is an analysis of radio observations of PSR J2256-1024, a BW pulsar with a spin period of 2.294531816964939(10)ms.Observing pulsars, we can calculate the arrival times of individual pulses and compare these with those predicted from various models to find the best-fitting one. This process is known as pulsar timing. We present the timing solution for PSR J2256-1024. We find it has a 5.1091831284(9)hr binary orbit with a semimajor axis of 4.1(3)ltsec and a 0.0312(9)M⊙ companion. PSR J2256-1024 shows a radio eclipse over 7.8% of its orbit - approximately twice the size of the Roche lobe calculated for the companion. This confirms the picture of a Black Widow pulsar with material being stripped from the companion and forming a trailing cloud which blocks the pulsar signal. We also find evidence for variable clumps of material in the system.We present polarization profiles and mean flux densities at 350 MHz, 820MHz and 1500 MHz. We discuss polarization changes in the post-eclipse region, where the pulsar signal is transmitted through eclipsing material in the system, and find evidence of Faraday rotation. At one epoch, synchronous measurements of excess dispersion and rotation measure lead to a detection of a 3.9(0.6)mG line-of-sight magnetic field. This field occurs an estimated minimum 3.3(0.3) companion-Roche-lobe-radii from the companion. We believe this is the first successful detection of a magnetic field component in eclipsing material within a Black Widow system.

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Wideband Timing of the Double Pulsar (PSR J0737-3039A) (2017)

Pulsars are neutron stars (NS) that produce beamed radio-frequency emission. Due to their rapid, steady rotation rate, this signal is detected as a series of pulses whose integrated profile is unusually stable over time. Pulsars in double neutron star (DNS) binary systems are a rare, but extremely useful, astronomical tool and have been used in tests of gravity theories in the strong-gravitational field limit. Rarer still are DNS systems in which both objects have been detected as pulsars; only one such system has been found thus far -- PSR J0737-3039A/B. Discovered over a decade ago, this system consists of one recycled pulsar, PSR J0737-3039A, and its companion, PSR J0737-3039B, which has since become undetectable.In any pulsar-related research, precise timing is necessary to produce meaningful results. The pulse time of arrivals (TOAs) are greatly affected by the medium through which the electromagnetic (EM) signal travels in both frequency-dependent and -independent ways. Even after accounting for such effects, many pulse profiles still exhibit frequency-dependent shape changes, which can greatly affect the precision of the timing results. Traditionally, corrections are applied to the TOAs after calculation in an ad hoc manner. In contrast to this, we explored the wideband timing algorithm developed by Timothy T. Pennucci and collaborators which accounts for frequency-dependent profile changes through a two-dimensional Gaussian pulse portrait model implemented in the TOA calculations. It was found that the portrait model is well-representative of the pulse profile shape over a wide frequency range. This method is also able to produce a robust set of wideband TOAs. The subsequent timing model, determined with TEMPO timing software, was found to be comparable to those produced from subbanded TOAs derived though more traditional methods. Some inconsistencies between the timing model astrometric and spin parameters of the wideband and subbanded data of this well-studied pulsar imply potential difficulties in achieving precise timing results not only for this pulsar, but for others, such as those used in pulsar timing arrays aiming to detect gravitational waves.

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The detectability of millisecond pulsars in eccentric binary systems (2013)

Experimental gravity with PSR B1534+12 (2012)

We present an updated analysis of pulse profiles and their arrival-times from PSR B1534+12, a 37.9-ms pulsar that is orbiting a neutron star. Such “double-neutron-star” systems are expected to undergo various relativistic effects, such as orbital decay and precession, due to the strong-field nature of the local gravitational field (Damour & Taylor, 1992). A high-precision timing model is derived that accounts for all astrophysical processes that systematically affect pulse arrival-times. In the process of generating this model, we constrain parameters that characterize the interstellar environment, relative motion of the pulsar, its spin properties, and binary parameters. We measure five “post-Keplerian” parameters that represent relativistic corrections to the standard Keplerian quantities that describe a binary orbit. These relativistic parameters are then used to test general relativity by comparing the measured values with those predicted by Einstein’s grav- itational theory. We conclude that general relativity is confirmed to within ∼ 0.35% of its predictions. The measurement of orbital decay contains a bias due to relative acceleration in the Galactic potential, and cannot be corrected for at this time due to an unreliable measure of distance; however, we can use this bias as a means to constrain the distance the pulsar should be from Earth in order for general relativity to be the correct theory of gravity. We find this distance to be d_GR = 1.037 ± 0.012 kpc. We also present evidence for pulse “jitter” in PSR B1534+12, which indicates short-term magnetospheric activity and has significant implications for the long-term improvement of timing precision. In a separate study, we present an analysis on pulse-profile evolution that has been previously linked to relativistic spin precession (Stairs et al., 2004). The current results of our precession analysis cannot confirm general relativity using this relativistic effect, but future studies and observations are needed to constrain the precession rate of PSR B1534+12.

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