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Kilonovae
The mergers of double neutron star (NS-NS) and black hole (BH)-NS binaries
are promising gravitational wave (GW) sources for Advanced LIGO and future GW
detectors. The neutron-rich ejecta from such merger events undergoes rapid
neutron capture (r-process) nucleosynthesis, enriching our Galaxy with rare
heavy elements like gold and platinum. The radioactive decay of these unstable
nuclei also powers a rapidly evolving, supernova-like transient known as a
"kilonova". Kilonovae provide an approximately isotropic electromagnetic
counterpart to the GW signal, which also provides a unique and direct probe of
an important, if not dominant, r-process site. This handbook reviews the
history and physics of kilonovae, leading to the current paradigm of week-long
emission with a spectral peak at near-infrared wavelengths. Using a simple
light curve model to illustrate the basic physics, I introduce potentially
important variations on this canonical picture, including: ~day-long optical
("blue") emission from lanthanide-free components of the ejecta; ~hours-long
precursor UV/blue emission, powered by the decay of free neutrons in the
outermost ejecta layers; and enhanced emission due to energy input from a
long-lived central engine, such as an accreting BH or millisecond magnetar. I
assess the prospects of detecting kilonovae following future GW detections of
NS-NS/BH-NS mergers in light of the recent follow-up campaign of the LIGO
binary BH-BH mergers.Comment: published in Living Reviews in Relativit
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