ASAS-SN search for optical counterparts of gravitational-wave events from the third observing run of Advanced LIGO/Virgo

TL;DR

This study used the ASAS-SN survey to search for optical counterparts to nine gravitational-wave events during LIGO/Virgo's third run, covering significant probability areas but finding no counterparts, demonstrating ASAS-SN's extensive coverage capabilities.

Contribution

The paper presents the first large-area optical coverage of gravitational-wave events by ASAS-SN, highlighting its rapid response and extensive sky coverage during LIGO/Virgo's O3 run.

Findings

No optical counterparts were detected.

ASAS-SN covered up to 60% of the probability area within 24 hours.

The survey achieved the largest coverage depth among similar surveys for these events.

Abstract

We report on the search for electromagnetic counterparts to the nine gravitational-wave events with a $>$60\% probability of containing a neutron star during the third (O3) LIGO-Virgo Collaboration (LVC) observing run with the All-Sky Automated Survey for SuperNovae (ASAS-SN). No optical counterparts associated with a gravitational wave event was found. However, thanks to its network of telescopes, the average area visible to at least one ASAS-SN site during the first 10 hours after the trigger contained $\sim$30\% of the integrated source location probability. Through a combination of normal operations and target-of-opportunity observations, ASAS-SN observations of the highest probability fields began within one hour of the trigger for four of the events. After 24 hours, ASAS-SN observed $>$60\% of total probability for three events and $>$40\% for all but one of the events. This is the largest area coverage to a depth of $g = 18.5$ mag from any survey with published coverage statistics for seven of the nine events. With its observing strategy, five sites around the world, and a large field of view, ASAS-SN will be one of the leading surveys to optically search for nearby neutron star mergers during LVC O4.