Research Developments in Li-Paczyński Novae (I): Theoretical Aspect

The neutron-rich matter ejected by compact object mergers (neutron star-neutron star merger and neutron star-black hole merger) provides one of the most important environments for the syntheses of r-process elements. In recent seventeen years, theoretical studies suggested that the energy produced during the decay of r-process elements will form optical/near infrared (NIR) radiations after thermalization. This type of optical/NIR transients are called Li-Paczyński novae, or LP-novae for short. Since the typical peak brightness of LP-novae is ∼1000 times brighter than that of a typical nova, they are also called Kilonovae. Besides, both theoretical and observational studies have showed, directly or indirectly, that under certain conditions, the compact object mergers can produce the gamma-ray bursts with a rather short duration of T90 ≤ 2s (SGRBs for short), and most SGRBs may come from compact object mergers. After the identification of SGRB afterglows, dedicated searches of the LP-novae associated with SGRBs have been taken. In this review we present the theoretical progress of LP-novae in recent seventeen years, and the observational aspect will appear in a upcoming paper.