Ejecta–Circumstellar Medium Interaction in High-density Environment Contribution to Kilonova Emission: Application to GRB 191019A

The nearby long-duration GRB 191019A recently detected by Swift lacks an associated supernova and belongs to a host galaxy with little star formation activity, suggesting that the origin of this burst is the result of a merger of two compact objects with dynamical interactions in a high-density medium of an active galactic nucleus. Given the potential motivation of this event, and given that it occurs in such a high-density environment, the ejecta–circumstellar medium (CSM) interaction cannot be ignored as possibly contributing to the kilonova emission. Here, we theoretically calculate the kilonova emission by considering the contribution of the ejecta–CSM interaction in a high-density environment. We find that the contribution to the kilonova emission from the ejecta–CSM interaction will dominate at a later time, and a smaller ejecta mass will have a stronger kilonova emission from the ejecta–CSM interaction. Moreover, we try to apply it to GRB 191019A, but we find that it is difficult to identify the possible kilonova emission from the observations, due to the contribution of the bright host galaxy. On the other hand, less injected mass (less than M ej = 2 × 10 −5 M ⊙ ) will be required if one can detect the kilonova emission associated with a GRB 191019A–like event in the future. The r -process-powered and spin energy contributions from the magnetar are also discussed.