The GALEX-PTF Experiment. II. Supernova Progenitor Radius and Energetics via Shock-cooling Modeling

Abstract

The radius and surface composition of an exploding massive star, as well as the explosion energy per unit mass, can be measured using early ultraviolet (UV) observations of core-collapse supernovae (CC SNe). We present the results from a simultaneous Galaxy Evolution Explorer (GALEX) and Palomar Transient Factory (PTF) search for early UV emission from SNe. We analyze five CC SNe for which we obtained near-UV (NUV) measurements before the first ground-based R -band detection. We introduce SOPRANOS, a new maximum likelihood fitting tool for models with variable temporal validity windows, and use it to fit the Sapir & Waxman shock-cooling model to the data. We report four Type II SNe with progenitor radii in the range of R * ≈ 600–1100 R ⊙ and a shock velocity parameter in the range of v s * ≈ 2700–6000 km s −1 ( E / M ≈ 2–8 × 10 50 erg/ M ⊙ ) and one Type IIb SN with R * ≈ 210 R ⊙ and v s * ≈ 11,000 km s −1 ( E / M ≈ 1.8 × 10 51 erg/ M ⊙ ). Our pilot GALEX/PTF project thus suggests that a dedicated, systematic SN survey in the NUV band, such as the wide-field UV explorer ULTRASAT mission, is a compelling method to study the properties of SN progenitors and SN energetics.