# Discrete and Continuous Ejection Models of the Radio Source Associated with GW170817

## TL;DR

This paper analyzes radio emissions from GW170817, using VLBI data to model ejection mechanisms and estimate energetics, providing new insights into the plasma dynamics post-merger.

## Contribution

It introduces discrete and continuous ejection models for GW170817's radio source, constraining jet power, plasmoid size, and energetics with unprecedented observational data.

## Key findings

- Discrete radio region moves at ~4c velocity
- Radio flux is contained within the discrete region
- Spectral turnover constrains plasmoid size and energetics

## Abstract

The gravity wave source, GW170817, and associated gamma ray burst (GRB), GRB 170817A, produced radio emission that was detected in multiple epochs of Very Long Baseline Interferometry (VLBI) and with broadband radio photometry. Three unique pieces of observational evidence were determined: a discrete radio emitting region that moves with an apparent velocity of $\approx 4$c, the discrete region includes all of the radio flux, and there is likely a synchrotron self absorption (SSA) spectral turnover on day $\sim 110$ and day $\sim 160$ after ejection. This unprecedented wealth of data for a GRB provides a unique opportunity to understand the radio emitting plasma that was ejected by the putative merger event. The velocity can constrain the kinematics and the SSA turnover has been used to constrain the size to much smaller than can be done with an unresolved VLBI image, allowing one to estimate the associated plasmoid size directly from the data and improve estimates of the energetics. Models of the radio emission for both a turbulent, protonic, discrete ballistic ejection and a high dissipation region within an otherwise invisible Poynting flux dominated positron-electron jet are considered. On days $\sim 110$ and $\sim 160$ post-merger, for the range of models presented, the jet power is $2\times 10^{39} - 8\times 10^{40} \rm{ergs/s}$ and the ballistic plasmoid kinetic energy is $3\times 10^{45} - 1.5\times 10^{47} \rm{ergs}$. Even though only valid after day 110, this independent analysis augments traditional GRB light curve studies, providing additional constraints on the merger event.