Two years of shock interaction tracing three phases of evolution: The explosion of a type IIn supernova, SN 2019vxm

Abstract

We present multiwavelength photometric and optical spectroscopic observations of the long-lived interacting supernova SN 2019vxm, spanning more than 2 yr after the explosion. SN 2019vxm is a slowly rising (rise time ∼ 43 days in the R-band), slowly declining supernova reaching an R-band peak absolute magnitude of ≈−20.3 mag. The SN light curve postmaximum shows a shallow decline, followed by a secondary, steeper decline in the optical (∼0.01 mag day−1), with late-time IR brightening. The total radiated luminosity is 5 × 10^50 erg, placing it among the energetic class of its type. We estimated a CSM mass of 3–8 M⊙ through light-curve modeling (independent of the CSM density profile) and by comparison with theoretical models. We estimate a minimum ejecta mass of ∼3.88 M⊙ from the broad Hα component, consistent with the ejecta mass obtained from the light-curve models. The solely interaction-dominated initial epochs are later accompanied by photonscattering signatures, leading to asymmetric line profiles with symmetric wings. The late phase, characterized by enhanced brightness at longer wavelengths and a stronger asymmetric line profile with the red side flux strongly suppressed, indicates the influence of preexisting or newly formed dust with temperatures ∼1600 K at ∼4 × 10^16 cm. Even in the late phases, no nebular lines are present in the spectra, indicating dense or obscured ejecta.