High Cadence TESS and ground-based data of SN 2019esa, the less energetic sibling of SN 2006gy

Abstract

We present photometric and spectroscopic observations of the nearby ($D\approx28$ Mpc) interacting supernova (SN) 2019esa, discovered within hours of explosion and serendipitously observed by the Transiting Exoplanet Survey Satellite (TESS). Early, high cadence light curves from both TESS and the DLT40 survey tightly constrain the time of explosion, and show a 30 day rise to maximum light followed by a near constant linear decline in luminosity. Optical spectroscopy over the first 40 days revealed a highly reddened object with narrow Balmer emission lines seen in Type IIn supernovae. The slow rise to maximum in the optical lightcurve combined with the lack of broad H$\alpha$ emission suggest the presence of very optically thick and close circumstellar material (CSM) that quickly decelerated the supernova ejecta. This CSM was likely created from a massive star progenitor with an $\dot{M}$ $\sim$ 0.3 M$_{\odot}$ yr$^{-1}$ lost in a previous eruptive episode 3--4 years before eruption, similar to giant eruptions of luminous blue variable stars. At late times, strong intermediate-width Ca II, Fe I, and Fe II lines are seen in the optical spectra, identical to those seen in the superluminous interacting SN 2006gy. The strong CSM interaction masks the underlying explosion mechanism in SN 2019esa, but the combination of the luminosity, strength of the H$\alpha$ lines, and mass loss rate of the progenitor all point to a core collapse origin.