K2 Observations of SN 2018oh Reveal a Two-component Rising Light Curve for a Type Ia Supernova
© 2018. The American Astronomical Society. All rights reserved.. We present an exquisite 30 minute cadence Kepler (K2) light curve of the Type Ia supernova (SN Ia) 2018oh (ASASSN-18bt), starting weeks before explosion, covering the moment of explosion and the subsequent rise, and continuing past peak brightness. These data are supplemented by multi-color Panoramic Survey Telescope (Pan-STARRS1) and Rapid Response System 1 and Cerro Tololo Inter-American Observatory 4 m Dark Energy Camera (CTIO 4-m DECam) observations obtained within hours of explosion. The K2 light curve has an unusual two-component shape, where the flux rises with a steep linear gradient for the first few days, followed by a quadratic rise as seen for typical supernovae (SNe) Ia. This "flux excess" relative to canonical SN Ia behavior is confirmed in our i-band light curve, and furthermore, SN 2018oh is especially blue during the early epochs. The flux excess peaks 2.14 ± 0.04 days after explosion, has a FWHM of 3.12 ± 0.04 days, a blackbody temperature of K, a peak luminosity of , and a total integrated energy of . We compare SN 2018oh to several models that may provide additional heating at early times, including collision with a companion and a shallow concentration of radioactive nickel. While all of these models generally reproduce the early K2 light curve shape, we slightly favor a companion interaction, at a distance of ∼ based on our early color measurements, although the exact distance depends on the uncertain viewing angle. Additional confirmation of a companion interaction in future modeling and observations of SN 2018oh would provide strong support for a single-degenerate progenitor system.
Dimitriadis, G; Foley, RJ; Rest, A; Kasen, D; Piro, AL; Polin, A; Jones, DO; Villar, A; Narayan, G; Coulter, DA; Kilpatrick, CD; Pan, YC; Rojas-Bravo, C; Fox, OD; Jha, SW; Nugent, PE; Riess, AG; Scolnic, D; Drout, MR; Barentsen, G; Dotson, J; Gully-Santiago, M; Hedges, C; Cody, AM; Barclay, T; Howell, S; Garnavich, P; Tucker, BE; Shaya, E; Mushotzky, R; Olling, RP; Margheim, S; Zenteno, A; Coughlin, J; Cleve, JEV; De Miranda Cardoso, JV; Larson, KA; McCalmont-Everton, KM; Peterson, CA; Ross, SE; Reedy, LH; Osborne, D; McGinn, C; Kohnert, L; Migliorini, L; Wheaton, A; Spencer, B; Labonde, C; Castillo, G; Beerman, G; Steward, K; Hanley, M; Larsen, R; Gangopadhyay, R; Kloetzel, R; Weschler, T; Nystrom, V; Moffatt, J; Redick, M; Griest, K; Packard, M; Muszynski, M; Kampmeier, J; Bjella, R; Flynn, S; Elsaesser, B; Chambers, KC; Flewelling, HA; Huber, ME; Magnier, EA; Waters, CZ; Schultz, ASB; Bulger, J; Lowe, TB; Willman, M; Smartt, SJ; Smith, KW; Points, S; Strampelli, GM; Brimacombe, J; Chen, P; Muñoz, JA; Mutel, RL; Shields, J; Vallely, PJ; Villanueva, S; Li, W; Wang, X; Zhang, J; Lin, H; Mo, J; Zhao, X; Sai, H; Zhang, X; Zhang, K; Zhang, T; Wang, L; Baron, E; Derkacy, JM
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