Two stripped envelope supernovae with circumstellar interaction -- but only one really shows it
J. Sollerman, C. Fransson, C. Barbarino, C. Fremling, A. Horesh, E., Kool, S. Schulze, I. Sfaradi, S. Yang, E. C. Bellm, R. Burruss, V., Cunningham, K. De, A. J. Drake, V. Z. Golkhou, D. A. Green, M. Kasliwal, S., Kulkarni, T. Kupfer, R. R. Laher, F. J. Masci, H. Rodriguez

TL;DR
This study compares two Type Ib supernovae with late-time re-brightening, revealing one with clear circumstellar interaction signatures and the other lacking such evidence, highlighting diverse CSM interaction phenomena.
Contribution
It provides detailed observational analysis of two supernovae, demonstrating contrasting evidence for circumstellar interaction in similar light curve behaviors.
Findings
SN 2019oys shows clear CSM interaction signatures in spectra and radio.
SN 2019tsf lacks spectral evidence of CSM interaction.
Both supernovae exhibit late-time re-brightening in light curves.
Abstract
We present SN 2019tsf (ZTF19ackjszs) and SN 2019oys (ZTF19abucwzt). These two stripped envelope Type Ib supernovae suddenly showed a (re-)brightening in their late light curves. We investigate this in the context of circumstellar material (CSM) interaction with previously ejected material, a phenomenon that is unusual among SE SNe. We analyse observational data, consisting of optical light curves and spectra. For SN 2019oys we also have detections in radio as well as limits from UV and X-rays. Both light curves show spectacular re-brightening after about 100 days. In the case of SN 2019tsf, the re-brightening is followed by a new period of decline, and the spectra never show signs of narrow emission lines that would indicate CSM interaction. On the contrary, SN 2019oys made a spectral makeover from a Type Ib to a spectrum clearly dominated by CSM interaction at the light curve…
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