WoU-MMA: Prompt and Afterglow Radio Signals from Neutron Star Mergers

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The merger of two ultra-compact stars, or neutron stars (NS), created the gravitational wave event, GW 170817. Investigation of the radio wave emission from the afterglow of GW170817 has provided key insights into the environment of the merger as well as the energy and morphology of the associated outflows. The late time confirmation of apparent superluminal motion has proved decisive in verifying the launch of a relativistic jet from the merger, as well as improving the use of mergers as "standard sirens" to constrain the Hubble constant of cosmology. With improved sensitivity of the gravitational wave detectors LIGO and Virgo, the next few years will begin an era when neutron star mergers will be routinely detected in the local universe. A research program at the California Institute of Technology (Caltech) will facilitate the discovery, follow up and interpretation of the radio afterglows from these mergers, produced by synchrotron light emission. The investigators will make use of awarded observing time on the NSF's Karl G. Jansky Very Large Array (VLA) and an approved program utilizing very long baseline interferometry (VLBI). Simultaneously, this program will support new efforts to search for prompt low-frequency counterparts to these same events. In addition, the investigators will develop a multi-faceted program involving student education spanning K-12 and undergraduate students. Three undergraduates will complete summer fellowships over the course of the project. The principal investigator (PI) will mentor six high school students from the Pasadena Unified School District to produce science fair projects themed on gravitational wave and multi-messenger astronomy. Finally, the PI will deliver three public lectures on gravitational wave sources to a broad audience via the Caltech Astronomy Stargazing and Public Lecture Series.LIGO and Virgo will uncover a new population of nearby NS mergers. A comprehensive census of radio afterglow emission from these mergers will give insights into the physics of central engines, ejecta morphology and local environments of the merger. VLBI observations will be crucial for constraining the geometry of the mergers and hence for enabling precise measurements of the Hubble constant that can potentially resolve the tension between the Planck/CMB-Type Ia supernova discrepancy. Radio observations may provide the only means to detect an electromagnetic counterpart for a significant fraction of the mergers (30% or more; especially NS-black hole mergers). The results from the proposed research will also help in addressing key open questions in broader astronomy, including binary star evolution and compact binary merger history of the universe. Finally, this research facilitates sensitive searches for prompt low-frequency radio counterparts of mergers, which, while theoretically speculative, offers an exciting prospect - a prompt or precursor counterpart to LIGO/Virgo detected events. This project advances the goals of the NSF Windows on the Universe Big Idea.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.