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

T. De Jaeger, B. J. Shappee, C. S. Kochanek, K. Z. Stanek, J. F. Beacom, T. W.S. Holoien, Todd A. Thompson, A. Franckowiak, S. Holmbo

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We report on the search for electromagnetic counterparts to the nine gravitational-wave events with a >60 per cent probability of containing a neutron star during the third observing run (O3) of the Laser Interferometer Gravitational-Wave Observatory (LIGO)-Virgo Collaboration (LVC) with the All-Sky Automated Survey for SuperNovae (ASAS-SN). No optical counterparts associated with a gravitational-wave event were found. However, thanks to its network of telescopes, the average area visible to at least one ASAS-SN site during the first 10 h after the trigger contained 30 per cent 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 1 h of the trigger for four of the events. After 24 h, ASAS-SN observed >60 per cent of total probability for three events and >40 per cent 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 fourth observation run (O4).

Original languageEnglish
JournalMonthly Notices of the Royal Astronomical Society
Pages (from-to)3427-3440
Number of pages14
Publication statusPublished - Jan 2022


  • black hole mergers
  • gravitational waves
  • neutron star mergers


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