Optimising the observation of optical kilonovae with medium size telescopes

TL;DR

This paper develops an optimized observing strategy for medium-sized telescopes to effectively distinguish kilonova models and viewing angles, recommending specific filters and observation cadences based on simulated light curves.

Contribution

It introduces a method using synthetic light curves to determine optimal observation sequences for kilonova follow-up with 2-meter telescopes.

Findings

Avoid using the u filter and colour curves for better results.

2-hour observation sequences are effective when distance error is ≤ 2%.

0.5-hour sequences are preferable when the source distance is unknown.

Abstract

We consider the optimisation of the observing strategy (cadence, exposure time and filter choice) using medium size (2-m class) optical telescopes in the follow-up of kilonovae localised with arcminute accuracy to be able to distinguish among various kilonova models and viewing angles. To develop an efficient observation plan, we made use of the synthetic light curves obtained with the Monte Carlo radiative transfer code POSSIS for different kilonova models and as a function of different viewing angles and distances. By adding the appropriate photon counting noise to the synthetic light curves, we analysed four alternative sequences having the same total time exposure of 8 hours, with different time windows (0.5, 1, 2, 4 h), each with $i$, $r$, and $u$ filters, to determine the observing sequence that maximises the chance of a correct identification of the model parameters. We suggest to avoid $u$ filter and to avoid the use of colour curves. We also found that, if the error on distance is $\le$ 2%, 0.5, 1, 2-hour time window sequences are equivalent, so we suggest to use 2-hour one, because it has 1 day cadence, so it can be easily realised. When the distance of the source is unknown, 0.5 h time window sequence is preferable.