Kilonova rates from spherical and axisymmetrical models

TL;DR

This paper compares spherical and axisymmetrical models of kilonovae to understand how model assumptions affect predicted detection rates and light curve shapes, finding that model choice significantly impacts rate estimates but not light curve morphology.

Contribution

It provides a detailed analysis of how different ejecta geometries influence kilonova detection rates and light curve features, highlighting the robustness of light curve shapes against ejecta layout variations.

Findings

The ratio of detection rates between spherical and axisymmetrical models is approximately 6:1 or 2:1.

Light curve shapes are only slightly affected by ejecta geometry.

Uncertainty in rate predictions due to ejecta distribution is negligible compared to other parameters.

Abstract

Detecting the thermal emission from double neutron star merger events is a challenging task because of the quick fading of the observed flux. In order to create an efficient observing strategy for their observing method it is crucial to know their intrinsic rate. Unfortunately, the numerous models existing today predict this rate on a vary wide range. Hence, our goal in this paper is to investigate the effect of different level of approximations on the relative rate predictions. Also, we study the effect of distinct ejecta mass lay-outs on the light curve. We find that the ratio of the expected kilonova detections of the spherical to axisymmetrical models is 6:1 (or 2:1, depending on the input parameter set applied in our work). Nevertheless, the light curve shape is only slightly affected by the various ejecta alignments. This means that different ejecta layouts can produce light curves with similar shapes making it a challenging task to infer the structure of the matter outflow. Thus, we conclude that the uncertainty in the rate predictions arising from the various ejecta mass distribution models is negligible compared to the errors present in other input parameters (e.g. binary neutron star merger rate). In addition, we show that up to moderate redshifts (z < 0.2) the redshift distribution type (observed or uniform in volume) does not affect the expected relative rate estimations.