SN 2024dy: Dust formation in a long-lived type IIn supernova and constraints on the dust mass

Abstract

Type IIn supernovae (SNe) are a subclass of core-collapse SNe powered by interaction between the ejecta and the dense circumstellar material. Among them, long-lived Type IIn events are characterized by luminous, long-duration light curves with high radiative energy. Several cases of long-lived type IIn SNe exhibit substantial dust emission at late times. However, well-observed examples remain limited, and the details of their dust formation mechanisms remain poorly understood. Here we present photometric and spectroscopic observations of the Type IIn SN 2024dy in ultraviolet, optical, and near-infrared (NIR) wavelength for 500 days. SN 2024dy reached a peak magnitude of Mr = −19.2 mag with a total radiation energy of 1.9 × 1050 erg. An NIR excess emerged at late phases, and the spectral energy distribution modeling indicates the presence of carbon dust with temperatures of 1300─1800 K and masses of about 10−5 M⊙. The spectra features were typical of long-lived Type IIn SNe. The late time Hα profile exhibits a strong suppression of the red wing, providing evidence for newly formed dust. Our results suggest that the derived dust mass above may be underestimated due to optical depth effects. SN 2024dy provides an important observational case for understanding dust formation in Type IIn SNe.