The Early Ultraviolet Light Curves of Type II Supernovae and the Radii of Their Progenitor Stars

• Published in: The Astrophysical journal 2024-07, Vol.970 (1), p.96
• Main Authors: Irani, Ido, Morag, Jonathan, Gal-Yam, Avishay, Waxman, Eli, Schulze, Steve, Sollerman, Jesper, Hinds, K-Ryan, Perley, Daniel A., Chen, Ping, Strotjohann, Nora L., Yaron, Ofer, Zimmerman, Erez A., Bruch, Rachel, Ofek, Eran O., Soumagnac, Maayane T., Yang, Yi, Groom, Steven L., Masci, Frank J., Aubert, Marie, Riddle, Reed, Bellm, Eric C., Hale, David
• Format: Article
• Language: English
• Subjects: Astrophysics; Blackbody; Constraint modelling; Core-collapse supernovae; Explosions; Ionization; Light curve; Luminosity; Physics; Plasma astrophysics; Shock cooling; Shocks; Skewed distributions; Supernovae; Transient sources; Type II supernovae; Ultraviolet astronomy; Ultraviolet radiation; Ultraviolet transient sources
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ad3de8

We present a sample of 34 normal Type II supernovae (SNe II) detected with the Zwicky Transient Facility, with multiband UV light curves starting at t ≤ 4 days after explosion, and X-ray observations. We characterize the early UV-optical color, provide empirical host-extinction corrections, and show that the t > 2 day UV-optical colors and the blackbody evolution of the sample are consistent with shock cooling (SC) regardless of the presence of “flash ionization” features. We present a framework for fitting SC models that can reproduce the parameters of a set of multigroup simulations up to 20% in radius and velocity. Observations of 15 SNe II are well fit by models with breakout radii 10 14 cm breakout radius. However, these fits predict an early rise during the first day that is too slow. We suggest that these large-breakout events are explosions of stars with an inflated envelope or with confined circumstellar material (CSM). Using the X-ray data, we derive constraints on the extended (∼10 15 cm) CSM density independent of spectral modeling and find that most SN II progenitors lose M ̇ < 10 − 4 M ⊙ yr − 1 up to a few years before explosion. We show that the overall observed breakout radius distribution is skewed to higher radii due to a luminosity bias. We argue that the 66 − 22 + 11 % of red supergiants (RSGs) explode as SNe II with breakout radii consistent with the observed distribution of RSGs, with a tail extending to large radii, likely due to the presence of CSM.