We present a comprehensive multi-epoch photometric and spectroscopic study of SN 2024bch, a nearby (19.9 Mpc) Type II supernova (SN) with prominent early high ionization emission lines. Optical spectra from 2.9 days after the estimated explosion reveal narrow lines of H I, He II, C IV, and N IV that disappear by day 6. High cadence photometry from the ground and TESS show that the SN brightened quickly and reached a peak MV∼−17.8 mag within a week of explosion, and late-time photometry suggests a 56Ni mass of 0.050 M⊙. High-resolution spectra from day 8 and 43 trace the unshocked circumstellar medium (CSM) and indicate a wind velocity of 30--40 km s−1, a value consistent with a red supergiant (RSG) progenitor. Comparisons between models and the early spectra suggest a pre-SN mass-loss rate of M˙∼10−3−10−2M⊙yr−1, which is too high to be explained by quiescent mass loss from RSGs, but is consistent with some recent measurements of similar SNe. Persistent blueshifted H I and [O I] emission lines seen in the optical and NIR spectra could be produced by asymmetries in the SN ejecta, while the multi-component Hα may indicate continued interaction with an asymmetric CSM well into the nebular phase. SN 2024bch provides another clue to the complex environments and mass-loss histories around massive stars.
@article{arxiv.2411.02497,
title = {Asymmetries and Circumstellar Interaction in the Type II SN 2024bch},
author = {Jennifer E. Andrews and Manisha Shrestha and K. Azalee Bostroem and Yize Dong and Jeniveve Pearson and M. M. Fausnaugh and David J. Sand and S. Valenti and Aravind P. Ravi and Emily Hoang and Griffin Hosseinzadeh and Ilya Ilyin and Daryl Janzen and M. J. Lundquist and Nicolaz Meza and Nathan Smith and Saurabh W. Jha and Moira Andrews and Joseph Farah and Estefania Padilla Gonzalez and D. Andrew Howell and Curtis McCully and Megan Newsome and Craig Pellegrino and Giacomo Terreran and Patrick Wiggins and Brian Hsu and Collin T. Christy and Noah Franz and Xiofeng Wang and Jialian Liu and Liyang Chen},
journal= {arXiv preprint arXiv:2411.02497},
year = {2025}
}