GW170817 4.5 Yr After Merger: Dynamical Ejecta Afterglow Constraints

Abstract GW170817 is the first binary neutron star (NS) merger detected in gravitational waves (GWs) and photons, so far remains only GW event of its class with a definitive electromagnetic counterpart. Radio emission from structured jet associated has faded below sensitivity achievable via deep radio observations most sensitive arrays currently operation. Hence, we now have opportunity to probe re-brightening that some models predict, which should emerge at late times interaction dynamically stripped ejecta interstellar medium. Here present latest results our field Karl G. Jansky Very Large Array (VLA), 4.5 yr after merger. Our new data 3 GHz do not show any compelling evidence for excess tail afterglow (<3.3 μ Jy), confirming previous results. We thus set constraints on dynamical models. These favor single-speed energies ≲10 50 erg (for an speed β 0 = 0.5), or steeper energy–speed distributions kilonova ejecta. also suggest larger values cold, nonrotating maximum NS mass equal-mass scenarios. However, without detection afterglow, obtaining precise equation state challenging.