Inferring CSM Properties of Type II SNe Using a Magnitude-Limited ZTF Sample

Although all Type II supernovae (SNe) originate from massive stars possessing a hydrogen-rich envelope, their light curve morphology is diverse, reflecting poorly characterised heterogeneity in the physical properties of their progenitor systems. Here, we present a detailed light curve analysis of a magnitude-limited sample of 639 Type II SNe from the Zwicky Transient Facility Bright Transient Survey. Using Gaussian processes, we systematically measure empirical light curve features (e.g. rise times, peak colours and luminosities) in a robust sampling-independent manner. We focus on rise times as they are highly sensitive to pre-explosion progenitor properties, especially the presence of a dense circumstellar medium (CSM) shed by the progenitor in the years immediately pre-explosion. By correlating our feature measurements with physical parameters from an extensive grid of STELLA hydrodynamical models with varying progenitor properties (CSM structure, $\dot{M}$, RCSM and MZAMS), we quantify the proportion of events with sufficient pre-explosion mass-loss to significantly alter the initial light curve (roughly MCSM ≥ 10−2.5M⊙) in a highly complete sample of 377 spectroscopically classified Type II SNe. We find that 67 ± 6 per cent of observed SNe in our magnitude-limited sample show evidence for substantial CSM (MCSM ≥ 10−2.5M⊙) close to the progenitor (RCSM < 1015 cm) at the time of explosion. After applying a volumetric-correction, we find 36$^{+5}_{-7}$% of all Type II SN progenitors possess substantial CSM within 1015 cm at the time of explosion. This high fraction of progenitors with dense CSM, supported by photometric and spectroscopic evidence of previous SNe, reveals mass-loss rates significantly exceeding those measured in local group red supergiants or predicted by current theoretical models.