Discovering and characterising compact mergers in wide-field surveys

  • Owen McBrien

Student thesis: Doctoral ThesisDoctor of Philosophy


This thesis concentrates on efforts to identify and characterize compact mergers involving neutron stars using wide-field survey instruments. With the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) and the Asteroid Terrestrial-impact Last Alert System (ATLAS), searches for compact mergers, including kilonovae, have been performed. The Pan-STARRS search identified two rapidly evolving transients with similar decline rates to the first kilonova, AT2017gfo, in PS15cey and PS17cke. While model fits of black hole-neutron star mergers can match the peak luminosity of PS15cey, a kilonova interpretation is less likely than a rapidly evolving supernova. PS17cke may be a plausible kilonova candidate, however, based on supporting modelling. The ATLAS search has returned no plausible kilonova candidates, but has identified a unique optical transient in AT2018kzr whose peak luminosity and rapid decline are difficult to describe using a traditional Nickel-56 driven explosion models. This necessitates the inclusion of an additional powering source, such as the spin-down of a magnetic neutron star remnant, to provide a plausible model fit to the bolometric lightcurve. Spectral modelling suggests the object is characterised by intermediate mass elements (including oxygen, silicone and magnesium) which disfavours a neutron star-neutron star merger scenario, but is consistent with predictions of white dwarfneutron star mergers. The lack of a kilonova detection by ATLAS has prompted the development of an efficiency simulation to understand the challenges of observing rapidly evolving and intrinsically faint transients with all-sky survey telescopes. Such a simulation has been used to constrain the volumetric rate of AT2017gfo-like transients in the local universe, with the results being consistent with other optically-derived rates estimates and rate of binary neutron star mergers measured gravitational wave observatories. Given the available information, it is predicted ATLAS will need to continue observing for at least a decade in order to observe a kilonova.
Date of AwardJul 2021
Original languageEnglish
Awarding Institution
  • Queen's University Belfast
SupervisorStephen Smartt (Supervisor) & Kate Maguire (Supervisor)


  • compact mergers
  • sky surveys
  • binary neutron star mergers

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