The discovery of gravitational-waves from a binary neutron-star merger on August 17^th, 2017 (GW170817) opened brave new opportunities in observational astrophysics. It was the fruit of a decades-long vision and the relentless pursuit of multimessenger-astrophysics with gravitational-waves (MMA). The Columbia Experimental Gravity (GECo) group is especially proud to be founders and pioneers of this emerging field of MMA. We are grateful to NSF for supporting and enabling our efforts in this field for decades. GECo members initiated and spearheaded LIGO's MMA with gamma-ray bursts, soft-gamma-repeaters, optical and other electromagnetic signatures, and neutrinos. Thanks to the foresight and systematic preparation efforts, the key components and connections were in place for LIGO's discoveries. Hundreds of astronomers not only expressed interest but also contributed with observations to complete the MMA mosaic of GW170817. Our multifaceted quest in GECo and the LSC are getting stronger, and a widening community is joining the worldwide effort in observing LIGO-Virgo-Kagra's discoveries.

Gravitational-wave information in near-real-time is essential for successful electromagnetic and neutrino observing campaigns. GECo developed the Low-Latency Algorithm for MMA Astrophysics (LLAMA) codebase and spearheaded near-real-time MMA observations during the LIGO-Virgo science runs. LLAMA enables to construct sophisticated statistical inference of joint events. For example, it can quantify whether a time-coincident neutrino observed by a partner detector is likely to be associated with a common cosmic source or if it is just a chance coincidence. LLAMA was running with low-latency and reporting results to the astronomy community during the past years using both high-energy neutrino and gravitational-wave data. NSF's IceCube detector - situated at the South Pole - was among our critical neutrino detector partners. A coincident neutrino, with a typical position uncertainty of ∼1deg², can significantly improve the inherently broad LIGO-Virgo localization. A joint gravitational-wave - high-energy neutrino discovery can be conveyed to the broader astronomy community within minutes of detection. The resulting tight sky localization and prompt response can enable the rapid detection in the electromagnetic regime. The joint search resulted in candidates with multiple coincidences that were followed-up by electromagnetic observatories. The partnership of the collaborations involved has proven that the international astrophysics community is ready to make the first joint gravitational-wave - astroparticle - and possibly electromagnetic counterpart discovery in real-time.

An additional goal for GECo for the past years has been to synthesize available measurements and theory, and thus aid future science extraction from gravitational-wave observation campaigns with a particular focus on binary black-hole events in situations where MMA counterparts may be observed. A promising scenario is when a black-hole binary merges within the disk of an Active Galactic Nucleus (AGN). GECo has extensively studied this case and reported on the likely properties of the black-holes and the AGN disk. Mergers in AGNs can also have plausible electromagnetic emissions. While the verdict is not yet out about what fraction of the observed binary black-hole mergers may originate from AGN disks, it is clear that AGNs can be origins of binary black-hole mergers. The astronomy community has taken interest and has been searching for electromagnetic counterparts to binary black-hole mergers and has already found a candidate event!

GECo also had mission-critical contributions in instrumentation and commissioning that enabled the first binary neutron star MMA detection and the milestone of the regular discovery of gravitational-waves from merging black-holes. During the second and third observation runs of the LIGO detectors, GECo continued to contribute to the proper operation of advanced LIGO, to characterize the performance of mission-critical detector subsystems and to prepare in-depth reports to support exceptional gravitational-wave candidates. Verified and precise timing information - including the timestamp and waveform of observed gravitational-wave events - not only enabled MMA observations coincident with other detectors, but it was also critical for constructing gravitational-wave skymaps. The quality of gravitational-wave sky localization, detector noise-floor, and MMA astronomy follow-ups are, therefore, all highly dependent on GECo's fundamental detector work.

The Columbia group has a strong outreach program driven by enthusiasm to share astrophysical results with a broad and diverse public. GECo members efficiently promoted the excitement, potential, and recognition of gravitational-wave science on multiple venues and forms. GECo members gave presentations for K-12 students, lab tours for high school students from underrepresented neighborhoods of the Bronx and Brooklyn. GECo conducted summer research seminars for New York-area high school students. For many years GECo exhibited on the promises of LIGO at the World Science Festival. GECo works with a diverse body of high-school students from New York area schools in addition to undergraduates. These motivated young people get much-needed encouragement/opportunity, critical laboratory exposure, and inspiration for future careers in science, technology, and math.

It is our honor to contribute at the forefront of Science and mentor the future of the Nation, with NSF.

Last Modified: 07/19/2020
Modified by: Szabolcs Marka