The interaction between the expanding supernova (SN) ejecta with the circumstellar material (CSM) that was expelled from the progenitor prior to explosion is a long-sought phenomenon, yet observational evidence is scarce. Here we confirm a new example: SN 2004dk, originally a hydrogen-poor, helium-rich Type Ib SN that reappeared as a strong Hα-emitting point-source on narrowband Hα images. We present follow-up optical spectroscopy that reveals the presence of a broad Hα component with full width at half maximum of ~290 km/s in addition to the narrow Hα +[NII] emission features from the host galaxy. Such a broad component is a clear sign of an ejecta-CSM interaction. We also present observations with the XMM-Newton Observatory, the Swift satellite, and the Chandra X-ray Observatory that span 10 days to 15 years after discovery. The detection of strong radio, X-ray, and Hα emission years after explosion allows various constraints to be put on pre-SN mass-loss processes. We present a wind-bubble model in which the CSM is "pre-prepared" by a fast wind interacting with a slow wind. Much of the outer density profile into which the SN explodes corresponds to no steady-state mass-loss process. We estimate that the shell of compressed slow wind material was ejected ~1400 yr prior to explosion, perhaps during carbon burning, and that the SN shock had swept up about 0.04 M_sun of material. The region emitting the Hα has a density of order 10−20 g/cc.
@article{arxiv.1910.06395,
title = {Interaction of SN~Ib 2004dk with a Previously-Expelled Envelope},
author = {David Pooley and J. Craig Wheeler and Jozsef Vinkó and Vikram V. Dwarkadas and Tamas Szalai and Jeffrey M. Silverman and Madelaine Griesel and Molly McCullough and G. H. Marion and Phillip MacQueen},
journal= {arXiv preprint arXiv:1910.06395},
year = {2019}
}