The Discovery of the First Optical Counterpart to a Gravitational Wave (GW) Source

Fundamental to answering the question, “How Did We Get Here?,” is answering the question, “Where Did the Elements Come From?”. Since 1957 we have known that nearly half of the naturally occurring elements heavier than iron in the Solar System (including gold, platinum, and uranium) are produced via a mechanism called "rapid neutron capture nucleosynthesis". However, a definitive astrophysical environment where this process occurs remained observationally unknown for 60 years. That picture changed on August 17th, 2017 when IGWN detected GWs from a coalescing binary neutron star system (BNS), GW170817. 1.7 seconds later, the Fermi and INTEGRAL gamma-ray telescopes detected a coincident short gamma-ray burst (sGRB), solidifying the theoretical connection between compact object mergers and sGRBs. ~11 hours later, and using my original software, I discovered the optical counterpart, the kilonova (KN) AT 2017gfo. My rapid and precise localization of the KN to its host galaxy NGC 4993 — in our ninth planned search image — resulted in the only spectrum within 24 hours of the GW trigger and was crucial to characterize its rapid evolution and confirm that NS mergers are indeed sites that forge the heaviest elements.

Paper: Swope Supernova Survey 2017a (SSS17a), the optical counterpart to a gravitational wave source

Selected Press Coverage:
The Atlantic: The Slack Chat That Changed Astronomy
National Geographic: In a First, Gravitational Waves Linked to Neutron Star Crash
Press Website: GW170817/SSS17a

Discovering and Characterizing High-z Supernovae (SNe)

Transient astronomy in the early, high-redshift (z > 3) Universe is an unexplored regime that offers the possibility of probing the first stars and the Epoch of Reionization. During Cycles 1 and 2 of the James Webb Space Telescope (JWST), the JWST Advanced Deep Extragalactic Survey (JADES) program enabled one of the first searches for transients in deep images (~ 30 AB mag) over a relatively wide area (25 arcmin2) -- resulting in ~80 newly discovered SNe. One transient, AT 2023adsv, was a likely SN IIP in a host with zspec=3.613 ± 0.001 and an inferred metallicity only 1/3 that of the local Universe. AT 2023adsv had bright rest-frame ultraviolet flux at the time of discovery, and we find a good match to a 20 M⊙ red supergiant progenitor star with an explosion energy of nearly twice that of normally observed SNe II in the local Universe. AT 2023adsv is the most distant photometrically classified SN IIP yet discovered with a spectroscopic redshift measurement, and may represent a global shift in SNe IIP properties as a function of redshift.

Paper: Discovery of a likely Type II SN at z=3.6 with JWST (submitted to ApJ)

Selected Press Coverage:
Space.com: James Webb Space Telescope discovers one of the earliest 'truly gargantuan' supernovas ever seen
Sky & Telescope: Supernovae Shaped the Early Universe, Webb Telescope Finds
AAS Press Conference: JWST Discovery of a Distant Supernova Linked to a Massive Progenitor in the Early Universe

Pushing the Envelope of Electromagnetic (EM) Follow-up to GWs

To address the challenge of searching for EM counterparts at larger distances with incomplete galaxy catalogs, I designed a new database called Teglon. Teglon leverages what we do know from heterogeneous galaxy surveys and generates a spatially varying, volumetric completeness metric. This metric is then convolved with a GW's 3D localization map to optimize a search network of small field-of-view (FoV; ≤ 1 deg2) search telescopes, and directs them to target galaxies in regions of high completeness, versus tessellating sky regions where this is not the case. During LIGO's third observing run (O3), I used Teglon to lead 1M2H in our combined UV, optical, and near IR search for the EM counterpart to the second-ever BNS merger discovered in GWs, GW190425. While no viable counterpart was detected by me or anyone else, I demonstrated how searching with Teglon provided up to an order-of-magnitude boost to the search efficiency for small FoV instruments. I combined our survey data with publicly reported data to produce the most comprehensive KNe, sGRB, and model-independent constraints on the EM emission from a hypothetical counterpart to GW190425 to date.

Paper: The Gravity Collective: A Comprehensive Analysis of the Electromagnetic Search for the Binary Neutron Star Merger GW190425 (submitted to ApJ)

Transient Science at Scale

In addition to my work in searching for EM counterparts, I am a leading member of the Young Supernova Experiment (YSE), a survey designed to discover thousands of supernovae (SNe) within a few hours to days from explosion. To operate at this scale, I wrote a transient survey management platform called YSE-PZ ('ēzē pēzē). YSE-PZ continually ingests streams of transient discoveries and metadata, and acts as a platform to run a variety of value-added services (e.g., host associations, light curve fitting, etc.) to provide team members with a detailed and coherent picture of a transient in real time. YSE-PZ has grown to become essential in supporting six different transient surveys simultaneously. I designed its architecture, lead its development, and it currently supports over 225 users and stores over 150,000 transients, 5.5 million photometry points, and 17,000 spectra, and has contributed to the publication of over 30 papers.

Paper: YSE-PZ: A Transient Survey Management Platform that Empowers the Human-in-the-Loop

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Some sights from around the world.