SN 2019cqc: A Hydrogen-rich Superluminous Supernova Showing Electron-scattering Signatures

Hydrogen-rich superluminous supernovae without narrow emission lines (SLSNe-II) are rare transients whose powering mechanisms remain debated, particularly the role of circumstellar medium (CSM) interaction. We present photometric and spectroscopic observations of SN 2019cqc to investigate its power source and progenitor mass loss. We model the lightcurve using MOSFiT with the csm and csmni models to constrain the explosion and CSM parameters. SN 2019cqc peaked at M g = −20.21 ± 0.07 and emitted ∼1.7 × 10 50 erg of energy in the form of radiation. Photometric and spectroscopic modeling indicates that CSM interaction dominates in both scenarios, with best-fit CSM and ejecta masses of ∼4.5 M ⊙ and ∼32 M ⊙ , respectively. The inferred CSM properties imply an extreme eruptive mass loss at a rate of ∼0.2–0.3 M ⊙ , yr −1 in the years preceding the core collapse, consistent with a variable progenitor of luminous blue variable progenitor. We observe a persistent blueshifted asymmetry in the H α emission line. At early times (≲+110 days), this is attributed to electron scattering with the bulk velocity of ejecta, while the profile at late epochs (≳ +402 days onward) suggests the subsequent formation of dust in the ejecta. Additionally, we identify a distinct, short-lived feature at ∼4600 Å, likely a blend of ionized C iii /N iii lines powered by the interaction of the SN-shock with the extended atmosphere.