A kilonova (KN or macronova) is an astronomical flash of EMR corresponding to an explosion more energetic than an "ordinary" nova but less than a supernova. It stems from the collision of two dense bodies. Typically it is 1000 times brighter than a nova but a tenth or a hundredth of a supernova. Much of the EMR from a kilonova is thought to occur in the infrared, making OIR observation useful. GW170817 is classified as a kilonova, confirming the theory that neutron star mergers produce them. The transient faded more rapidly than a supernova.
Models developed for kilonovae have been classified as blue kilonova models versus red kilonova models, the color names used to indicate a shorter versus longer wavelength EMR rather than the actual colors: both deal with peaks in the near infrared. The red models would be producing more lanthanides and the blue, more. GW170817 shows some of each, with "red model" characteristics revealed after "blue model" characteristics had subsided.