Institute for Advanced Study Informal Astrophysics Seminar

I will describe recent work on the observable signatures of compact object birth in two situations. The first scenario is the coalescence of binary neutron stars, the primary source for the direct detection of gravitational waves by Advanced LIGO. A generic feature of such mergers and their aftermath is the ejection of neutron-rich material, which synthesizes heavy radioactive elements as it expands away from the merger site. Thermal emission produced by the decay of these nuclei powers a dim optical transient known as a `kilonova'. I will show how the colors and duration of the kilonova may encode information about the post-merger evolution (in particular, the time of black hole formation) not otherwise available in the detected gravitational waveform. The second scenario I will describe is the formation of a rapidly rotating, strongly magnetized neutron star (a `millisecond magnetar') following the core collapse of a massive star. The birth of such objects has been suggested to explain a recently discovered class of `super-luminous' supernovae. I will present a model for the evolution of young millisecond pulsar wind nebulae that describes how their non-thermal radiation `thermalizes' with the surrounding opaque ejecta, producing anomalously bright optical emission. Nebular X-rays may be sufficiently luminous to re-ionize--and hence to escape from--the ejecta within months after the explosion, providing a potential `smoking gun' test of the magnetar model.