Speaker
Description
We investigate the thermal emission and extinction from dust associated with a nearby superluminous supernova (SLSN) at $z=0.0267$, SN~2018bsz, in order to determine its nature. We use the 7-channel imager GROND to extensively monitor the photometric evolution of SN~2018bsz. This is the first dataset with daily cadence and simultaneous optical and near-infrared (NIR) coverage for a SLSN. At $+230$ days, the SN is not detected in the optical and shows significant NIR excess, with $r-J>3$ mag and $r-K_{\mathrm{s}}>5$ mag. We use the $\textit{Spitzer Space Telescope}$ to detect the SN at late-times between $+384$ and $+535$ days in 3.6 and 4.5 $\mu$m images. In addition, we recover NEOWISE detections at 3.4 and 4.6 $\mu$m for SN~2018bsz between $+68$ and $+423$ days. The time evolution of the IR lightcurve enables us to investigate whether the mid-infrared emission is from newly formed dust inside the SN ejecta or from a pre-existing circumstellar envelope or interstellar material heated by the radiation from the SN. We find the later two scenarios can be ruled out, and a scenario where new dust is forming at epochs $>200$ days can self-consistently reproduce the evolution of the SN flux. We can fit the spectral energy distribution well between $+230$ and $+380$ days with $5\times10^{-4}$ $M_{\odot}$ of carbon dust, subsequently a higher dust mass of $10^{-2}$ $M_{\odot}$ is required. SN~2018bsz is the first SLSN showing evidence for dust formation within the SN ejecta, and it could potentially provide an analog for dust formation in the early Universe.
