Nucleosynthesis in outflows of compact objects and detection prospects of associated kilonovae

Abstract

We perform a comparative analysis of nucleosynthesis yields from binary neutron star (BNS) mergers, black hole-neutron star (BHNS) mergers, and core-collapse supernovae (CCSNe) with the goal of determining which are the most dominant sources of r-process enrichment observed in stars. We find that BNS and BHNS binaries may eject similar mass distributions of robust r-process nuclei post merger (up to 3rd peak and actinides, A ∼ 200 − 240), after accounting for the volumetric event rates. Magnetorotational (MR) CCSNe likely undergo a weak r-process (up to A ∼ 140) and contribute to the production of light element primary process (LEPP) nuclei, whereas typical thermal, neutrino-driven CCSNe only synthesize up to 1st r-process peak nuclei (A ∼ 80 − 90). We also find that the upper limit to the rate of MR CCSNe is $\lesssim 1~{{\%}}$ the rate of typical thermal CCSNe; if the rate was higher, then weak r-process nuclei would be overproduced. Although the largest uncertainty is from the volumetric event rate, the prospects are encouraging for confirming these rates in the next few years with upcoming surveys. Using a simple model to estimate the resulting kilonova light curve from mergers and our set of fiducial merger parameters, we predict that ∼7 BNS and ∼2 BHNS events will be detectable per year by the Vera C. Rubin Observatory (LSST), with prior gravitational wave (GW) triggers.

Magnetized Outflows from Short-lived Neutron Star Merger Remnants Can Produce a Blue Kilonova

“…In a follow-up work, we will model a longer-lived NS remnant and perform multidimensional kilonova calculations, tracking ejecta from the moment of launch to the kilonova phase. Our work complements ongoing efforts to model populations of kilonovae and determine observing strategies for upcoming surveys such as LSST (Ekanger et al 2023;Setzer et al 2023). Such efforts need to take NS remnant outflows into consideration in order to capture the full spectrum of kilonova transients.…”

Exploring the Impact of the Ejecta Velocity Profile on the Evolution of Kilonova: Diversity of the Kilonova Lightcurves

“…To date, only a few kilonovae have been observed, mainly because of their short lifetimes and relatively low luminosities. However, with the enhancement of follow-up strategies using current telescopes and also with the development of advanced future telescopes like the 7-Dimensional Telescope (Im 2021), the chances of detecting kilonovae are expected to increase significantly (e.g., Cowperthwaite et al 2019;Chase et al 2022;Ekanger et al 2023). In this circumstance, this work proposes a model to explain peculiar kilonova lightcurves that might be observed in the near future.…”

A Perspective on the Milky Way Bulge Bar as Seen from the Neutron-capture Elements Cerium and Neodymium with APOGEE

“…Since the gravitational wave detection from the neutron star merger GW170817 (Abbott et al 2017) and subsequent spectroscopic observations (Watson et al 2019), neutron star mergers are probably the main producers of rprocess elements, as predicted by modern simulations (Thielemann et al 2017). Recently, Ekanger et al 2023 confirmed that black hole-neutron star mergers also produce a significant amount of r-process elements through nucleosynthesis yields from numerical simulations, as indicated by previous studies as well (e.g., Lattimer & Schramm 1976;Freiburghaus et al 1999;Nishimura et al 2016;Kobayashi et al 2023). The r-process also happens at other astrophysical sites, such as core-collapse supernovae (e.g., Wheeler et al 1998;Ekanger et al 2023) and magnetorotational supernovae (e.g., Winteler et al 2012;Reichert et al 2021Reichert et al , 2023.…”

“…Recently, Ekanger et al 2023 confirmed that black hole-neutron star mergers also produce a significant amount of r-process elements through nucleosynthesis yields from numerical simulations, as indicated by previous studies as well (e.g., Lattimer & Schramm 1976;Freiburghaus et al 1999;Nishimura et al 2016;Kobayashi et al 2023). The r-process also happens at other astrophysical sites, such as core-collapse supernovae (e.g., Wheeler et al 1998;Ekanger et al 2023) and magnetorotational supernovae (e.g., Winteler et al 2012;Reichert et al 2021Reichert et al , 2023. The contribution of core-collapse and magnetorotational supernovae to the abundance of rprocess elements is currently under debate.…”