High-Cadence TESS and Ground-based Data of SN 2019esa, the Less Energetic Sibling of SN 2006gy ∗

Abstract

Abstract We present photometric and spectroscopic observations of the nearby (D ≈ 28 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 reddened object with narrow Balmer emission lines seen in Type IIn SNe. The slow rise to maximum in the optical light curve combined with the lack of broad Hα emission suggest the presence of very optically thick and close circumstellar material (CSM) that quickly decelerated the SN ejecta. This CSM was likely created from a massive star progenitor with an M ̇ ∼ 0.2 M ☉ yr−1 lost in a previous eruptive episode 3–4 yr 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 Hα lines, and mass-loss rate of the progenitor seem to be inconsistent with a Type Ia CSM model and instead point to a core-collapse origin.