Core collapse supernovae:
We have discovered, followed and studied a number of rare supernovae. Rare events provide unique clues regarding possible missing physical insights in our models. We studied an event from a rare class of explosions (called Type Ibn) which occur from stars that lost all of their hydrogen prior to explosion, and were likely in the process of losing their helium. Using our observations, we were able to confirm that such explosions require recent mass loss to have occurred, and to constrain the parameters and type of mass loss. We also studied an event from the most common type of stellar explosions (Type IIP), and showed that it, surprisingly, suffered no mass loss prior to explosion. These discoveries provide stringent constraints for models of massive star evolution, especially during their final, and currently most uncertain, stages. In parallel we have modeled the evolutionary paths of actual supernova progenitors (seen before the explosion), that lost mass before the explosion, in order to better understand the causes and conditions leading to this mass loss. In addition, we have developed a new method to study the oscillations of massive stars, which hold vital clues as to their still uncertain internal structure.
Tidal Disruption Events:
We discovered several new events, of this very rare class of astronomical transients, in their early phases, before reaching maximum brightness, as well as one event with a dust echo formed closer to the black hole than ever observed before. These observations have revealed new phenomena in the way the light from these events evolve, providing clues regarding the still debated emission physics of stellar accretion and disruption by black holes. We have also quantified the relative rates of such events in various types of galaxies, and using various types of search filters in transient alert streams. This informs, not only models of the physics leading to these events, but also strategies on how to find more of them in existing and future astronomical surveys.
Neutron-Star Mergers:
Given the lack of new gravitational-wave events, and delays in re-starting gravitational-wave detectors, we have focused on analyzing our, as well as the community’s follow-up strategies during previous gravitational-wave detector observing runs, and on building tools to improve these strategies. In parallel, we searched for neutron-star mergers without gravitational-waves, and while we didn’t find any, we did find other intriguing events, and were able to set limits on the rates of neutron-star mergers.
