Yang Hu

Thursday 24 Apr 2025, 13:15 → 14:15 Europe/Stockholm

A5:1003

Title:
When CSM Outmasses Ejecta: the Case of Hydrogen-Rich Superluminous Supernovae 2021aaev
Abstract
Hydrogen-rich superluminous supernovae (SLSNe-II), characterised by their extreme peak luminosity (≤ -20 mag in optical), represent a rare subclass of supernovae (SNe). While a handful have been observed with medium- or high-resolution spectroscopy (most showing narrow H lines; SLSNe-IIn), two key questions persist: (1) Are SLSNe-IIn simply the luminous extreme of the SN IIn population? (2) What are the characteristic circumstellar medium (CSM) parameters that power SLSNe-IIn? Here, we present extensive photometric and spectroscopic observations of SN 2021aaev, a SLSN-IIn at z = 0.1557 with a rise time of 32.5 ± 1.0 days and a peak luminosity of -21.35 ± 0.03 mag (ATLAS o-band). Its early spectra resemble SNe IIn but reveal persistent flash-ionisation features lasting >1 week, marking it as the first SLSN-II flasher. Its late photospheric spectra diverge from typical SNe IIn and show similarity to SN 2017hcc (a SLSN-IIn), with the persistent narrow Hα up to +96 days since first light. Our analysis indicates interaction between 1-5 M☉ of ejecta and an extensive (≥10^16 cm), heavy (≥2 Mej) CSM. This makes SN 2021aaev a compelling case for understanding the diversity within SLSNe-II and the connection (or lack thereof) between SLSNe-IIn and SNe IIn.