The Fastest Path to Discovering the Second Electromagnetic Counterpart to a Gravitational Wave Event

TL;DR

This study uses simulations to compare strategies for discovering the second electromagnetic counterpart to a gravitational wave event, finding that extending current observing runs can lead to faster discovery than waiting for upgrades.

Contribution

The paper provides a comprehensive simulation-based analysis of observing strategies, highlighting the benefits of extending current runs over waiting for detector upgrades for timely counterpart discovery.

Findings

Extending O4 can lead to earlier kilonova discovery by approximately 125 days.

Continuing O4 is often more effective than waiting for the O5 upgrade.

Avoiding long gaps between discoveries is critical for multi-messenger astronomy.

Abstract

The discovery of a second electromagnetic counterpart to a gravitational wave event represents a critical goal in the field of multi-messenger astronomy. In order to determine the optimal strategy for achieving this goal, we perform comprehensive simulations comparing two potential paths forward: continuing the current LIGO-Virgo-KAGRA (LVK) observing run, O4, versus temporarily shutting down the detectors for upgrades before beginning the next observing run, O5. Our simulations incorporate current O4 instrument sensitivities and duty cycles, as well as projected configurations for O5, while accounting for variables such as binary neutron star merger rates, system properties, viewing angles, dust extinction, and kilonova (KN) observables. Our results indicate that a KN discovery would occur $125^{+253}_{-125}$~days (middle 50\% interval) sooner in O5 compared to O4, suggesting that extending O4 would lead to faster discovery if the shutdown period between runs is $>$4~months. Moreover, for 88\% of our simulations, continuing O4 results in earlier KN discovery when compared to the expected two-year shutdown between O4 and O5. Given these findings and the critical importance of avoiding a $>$10 year gap between first and second electromagnetic counterpart discoveries, we suggest LVK consider extending O4 operations for as long as feasible prior to shutting down for critical upgrades.