Can kilonova light curves be standardized?

Abstract

Binary neutron star (NS) mergers have been recently confirmed to be the progenitors of the optical transients kilonovae (KNe). KNe are powered by the radioactive decay of neutron-rich elements (r-process elements), which are believed to be the product of disruption of NSs during their merger. KNe exhibit interesting parallels with SNe Ia, whose light curves show specific correlations that allow them to be used as standardizable candles. In this Letter, we investigate whether KNe light curves could exhibit similar correlations. While a satisfactory answer to this question can only be provided by future KNe observations, employing theoretical models we explore whether there is any ground for harboring such expectations. Using semi-analytic models of KNe light curves in conjunction with results from numerical relativity simulations of binary NS mergers, we obtain the maximum bolometric luminosity (L^max_Bol) and decline from peak luminosity (ΔlogL_Bol) for a simulated population of mergers. We find that theoretical light curves of KNe show remarkable correlations despite the complex physics governing their behavior. This presents a possibility of future observations to uncover such correlations in the observed light curves, eventually allowing observers to standardize these light curves and to use them for local distance measurements.