IPTF14hls in the Circumstellar Medium Interaction Model: A Promising Candidate for a Pulsational Pair-instability Supernova

Abstract

iPTF14hls is a luminous Type II supernova (SN) with a bumpy light curve whose origin remains under debate. It maintains a roughly constant effective temperature and luminosity for about 600 days after discovery, followed by a slow decay. About ∼1000 days after discovery, the light curve transitions to a very steep decline. A spectrum taken during this steep-decline phase shows clear signatures of a shock interaction with a dense circumstellar medium (CSM). Here, we explore the possibility of iPTF14hls as an interaction-powered SN. The light curve of iPTF14hls can be fitted with wind-like CSMs. Analytic modeling indicates that iPTF14hls may have undertaken six episodes of mass loss during the last ∼200 yr. Assuming that the 1954 eruption triggered the last mass-loss episode, the stellar wind velocity is determined to be 40−70 km s−1, depending on different models. Mass-loss rates are in the range 0.4–3.3M ⊙ yr−1. The inferred total mass of the ejecta and CSMs (M ej + M CSMs ≃ 245M ⊙) supports the idea that iPTF14hls may be a candidate for a (pulsational) pair-instability SN. Discoveries and observations of similar stellar explosions will help us to understand these peculiar SNe.