  GW170817 is the first binary neutron star (NS) merger detected in
gravitational waves (GWs) and photons, and so far remains the only GW event of
its class with a definitive electromagnetic (EM) counterpart. Radio emission
from the structured jet associated with GW170817 has faded below the
sensitivity achievable via deep radio observations with the most sensitive
radio arrays currently in operation. Hence, we now have the opportunity to
probe the radio re-brightening that some models predict, should emerge at late
times from the interaction of the dynamically-stripped merger ejecta with the
interstellar medium. Here we present the latest results from our deep radio
observations of the GW170817 field with the Karl G. Jansky Very Large Array
(VLA), 4.5 years after the merger. Our new data at $3\,$GHz do not show any
compelling evidence for emission in excess to the tail of the jet afterglow
($<3.3\,\mu$Jy), confirming our previous results. We thus set new constraints
on the dynamical ejecta afterglow models. These constraints favor single-speed
ejecta with energy $\lesssim 10^{50}\,$erg (for an ejecta speed of
$\beta_0=0.5$), or steeper energy-speed distributions of the kilonova ejecta.
Our results also suggest larger values of the cold, non-rotating maximum NS
mass in equal mass scenarios. However, without a detection of the dynamical
ejecta afterglow, obtaining precise constraints on the NS equation of state
remains challenging.
