Collaborative Proposal: Enhanced Gravitational Wave Search via Simultaneous Advanced LIGO/Virgo and Evryscope Detection

University Of North Carolina At Chapel Hill, Chapel Hill NC

Investigators

Abstract

The recent gravitational wave (GW) detection of the first binary neutron star (BNS) merger by the LIGO/Virgo gravitational wave observatories and its associated electromagnetic (EM) counterparts has ushered in a new era of multi-messenger astrophysics. The GW170817 event has inspired a new GW search strategy using simultaneous all-sky optical imaging measurements to provide improved detection confidence as well as source identification/localization. This grant will fund the development and testing of this improved GW search in Advanced LIGO/Virgo (aLIGO/Virgo) operation run 3 (O3), with the potential to substantially increase the number of confirmed GW detections. This will significantly improve the progress of science in the national interest by leveraging the existing investments in gravitational wave and optical observatories to provide an estimated ~25% enhancement in the number of detected systems during O3, and pave the way for future multi-messenger investigations that could potentially quadruple the number of detected sources. The proposed research is at the intersection of the multi-messenger astrophysics, general relativity, digital signal processing and computing, which require young researchers to develop a deep knowledge of modern astrophysical theories, and understanding of gravitational wave instrumentation, and gives them opportunity to get firsthand experience with sophisticated signal/image-processing algorithms, computational methods, manipulation of large data sets and high performance computing. The novel GW search proposed here is based on combining aLIGO/Virgo sub-threshold triggers with simultaneous optical imaging using the Evryscope technique. Evryscope images the entire observable night-time sky simultaneously with 2-minute cadence. Scientists can then select only those optical transient events in the aLIGO/Virgo error region which appear within the same 2-minute window as the GW candidate - reducing the GW-only false alarm probability by factors larger than 20,000. for any night-time GW events. This enables improved detection confidence for marginal GW events and thus enhanced GW detection volume. GW1708187's optical counterpart could be detected by the current Evryscope out to D ~260 Mpc, and future Evryscope-style systems to distances further than 350 Mpc. Analyses show that a future network of Evryscope-style detectors would enhance the number of GW events detected by a factor of ~2-4 compared to GW-only observations. Such a future network would particularly benefit GW source population studies and cosmological applications of GW events. This approach will also provide coverage of the brightest portion of the optical lightcurve, and arcsecond-level localization for all of these events, which will dramatically improve the EM followup response from the community as a whole, leading to improved astrophysical context for interpreting the implications of the GW event. The proposed work here is to carry out a sub-threshold GW search in aLIGO/Virgo O3, using the Evryscope North and South facilities for simultaneous optical coverage. Based on the properties of GW170817's GW properties, optical counterpart, and analyses presented here, such a search could add an additional ~25% more detections to the number of confirmed BNS mergers in O3. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.