Detecting electromagnetic counterparts to LIGO/Virgo/KAGRA gravitational wave events with DECam: Neutron Star Mergers

TL;DR

This study develops end-to-end simulations of LVK O4 and O5 gravitational-wave events to optimize electromagnetic follow-up of neutron-star mergers with the DECam-based GW-MMADS program. By combining a data-driven GW population (BNS and NSBH) with KN light-curve surrogates and an optimized tiling strategy, the authors forecast sky localizations, KN detectability, and practical telescope time needs under realistic detector sensitivities and duty cycles. They find that including Virgo improves localization and increases the fraction of well-localized events, and they quantify how KN detectability depends on chirp mass, mass ratio, viewing angle, and remnant fate, across multiple EOS scenarios. The results yield actionable guidance for follow-up campaigns, including anticipated detection rates, required depths, and feasible observing cadences, and the authors provide public GW simulations and KN-depth tables to support the community’s multimessenger efforts.

Abstract

With GW170817 being the only multimessenger gravitational wave (GW) event with an associated kilonova detected so far, there exists a pressing need for realistic estimation of the GW localization uncertainties and rates, as well as optimization of available telescope time to enable the detection of new kilonovae. We simulate GW events assuming a data-driven distribution of binary parameters for the LIGO/Virgo/KAGRA (LVK) fourth and fifth observing runs (O4 and O5). We map the binary neutron star (BNS) and neutron star-black hole (NSBH) properties to the kilonova optical light curves. We use the simulated population of kilonovae to generate follow-up observing plans, with the primary goal of optimizing detection with the Gravitational Wave Multi-Messenger Astronomy DECam Survey (GW-MMADS). We explore the dependence of kilonova detectability on the mass, distance, inclination, and spin of the binaries. Assuming that no BNS was detected during O4 until the end of 2024, we present updated GW BNS (NSBH) merger detection rates. We expect to detect BNS (NSBH) kilonovae with DECam at a per-year rate of: $0$-$2.0$ ($0$) in O4, and $2.0$-$19$ ($0$-$1.0$) in O5. We expect the majority of BNS detections and also those accompanied by a detectable kilonova to produce a hypermassive NS remnant, with a significant fraction of the remaining BNSs promptly collapsing to a BH. We release GW simulations and depths required to detect kilonovae based on our predictions to support the astronomical community in their multimessenger follow-up campaigns and analyses.

Figures (12)

• Figure 1: Cumulative distribution of sky localization area at 50, 70, and 90$\%$ credible intervals for simulations 1 (black line), 2 (red line), and 3 (blue line) for BNS (top) and NSBH (bottom) events. The median localization area for each configuration is annotated in the respective panel.
• Figure 2: 90$\%$ CI area versus luminosity distance for BNS (top) and NSBH (bottom) events with the same color scheme as in Figure \ref{['fig:w_Virgo']}.
• Figure 3: Cumulative distribution of volume and distance for BNS (top) and NSBH (bottom) at 90$\%$ credible intervals for the 3 simulations using the same color scheme as in Figure \ref{['fig:w_Virgo']}. The median distance or volume for each configuration is annotated in the respective panel.
• Figure 4: Chirp mass versus luminosity distance for BNS (left) and NSBH (right) events in the O5 simulation. The yellow squares represent all BNS/NSBH detected in gravitational waves, the cyan squares show all mergers for which a KN is produced according to our model and fiducial EOS. Out of all the KNe, those with a black point and/or a red circle were detected in $g$ and/or $i$ band, respectively. The same color scheme applies to the histograms. We limit the plot to a chirp mass of $3.5~{M_{\odot}}$ for the NSBH since no KN is produced beyond this chirp mass in our simulations. For both cases, the lower chirp mass end of the distribution yields higher KN detection rates than at larger mass.
• Figure 5: Mass ratio versus chirp mass for the BNS merger events (left panel) and NSBH mergers (right panel) from the O5 simulation. The color scheme is the same as in Figure \ref{['fig:tm_dis']}.