Departmental Oral Examination (Thesis Title: "Mass and Geometric Measurements of Binary Radio Pulsars")

Event Date and Time: 
Thu, 2016-07-07 10:00 - 12:00
Room 309, Hennings Building
Local Contact: 
Physics and Astronomy, UBC
Intended Audience: 

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 15 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 pulsar masses and make new detections of the Shapiro-delay signal in four pulsar-binary systems for the first time. In the relativistic PSR B1534+12 binary system, we derive an precise rate of geodetic precession of the pulsar-spin axis -- observed as a secular variation in electromagnetic pulse structure -- that is consistent with the prediction from general relativity, for the first time. 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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