K2 Observations of SN 2018oh Reveal a Two-Component Rising Light Curve for a Type Ia Supernova
Creators: name: Dimitriadis, G.
name: Foley, R. J.
name: Rest, A.
name: Kasen, D.
name: Piro, A. L.
name: Polin, A.
name: Jones, D. O.
name: Villar, A.
name: Narayan, G.
name: Coulter, D. A.
name: Kilpatrick, C. D.
name: Pan, Y. -C.
name: Rojas-Bravo, C.
name: Fox, O. D.
name: Jha, S. W.
name: Nugent, P. E.
name: Riess, A. G.
name: Scolnic, D.
name: Drout, M. R.
name: Barentsen, G.
name: Dotson, J.
name: Gully-Santiago, M.
name: Hedges, C.
name: Cody, A. M.
name: Barclay, T.
name: Howell, S.
name: Garnavich, P.
name: Tucker, B. E.
name: Shaya, E.
name: Mushotzky, R.
name: Olling, R. P.
name: Margheim, S.
name: Zenteno, A.
name: Coughlin, J.
name: Van Cleve, J. E.
name: Cardoso, J. Vinicius de Miranda
name: Larson, K. A.
name: McCalmont-Everton, K. M.
name: Peterson, C. A.
name: Ross, S. E.
name: Reedy, L. H.
name: Osborne, D.
name: McGinn, C.
name: Kohnert, L.
name: Migliorini, L.
name: Wheaton, A.
name: Spencer, B.
name: Labonde, C.
name: Castillo, G.
name: Beerman, G.
name: Steward, K.
name: Hanley, M.
name: Larsen, R.
name: Gangopadhyay, R.
name: Kloetzel, R.
name: Weschler, T.
name: Nystrom, V.
name: Moffatt, J.
name: Redick, M.
name: Griest, K.
name: Packard, M.
name: Muszynski, M.
name: Kampmeier, J.
name: Bjella, R.
name: Flynn, S.
name: Elsaesser, B.
name: Chambers, K. C.
name: Flewelling, H. A.
name: Huber, M. E.
name: Magnier, E. A.
name: Waters, C. Z.
name: Schultz, A. S. B.
name: Bulger, J.
name: Lowe, T. B.
name: Willman, M.
name: Smartt, S. J.
name: Smith, K. W.
name: Points, S.
name: Strampelli, G. M.
name: Brimacombe, J.
name: Chen, P.
name: Munoz, J. A.
name: Mutel, R. L.
name: Shields, J.
name: Vallely, P. J.
name: Villanueva, S.
name: Li, W.
name: Wang, X.
name: Zhang, J.
name: Lin, H.
name: Mo, J.
name: Zhao, X.
name: Sai, H.
name: Zhang, X.
name: Zhang, K.
name: Zhang, T.
name: Wang, L.
name: Zhang, J.
name: Baron, E.
name: DerKacy, J. M.
name: Li, L.
name: Chen, Z.
name: Xiang, D.
name: Rui, L.
name: Wang, L.
name: Huang, F.
name: Li, X.
name: Hosseinzadeh, G.
name: Howell, D. A.
name: Arcavi, I.
name: Hiramatsu, D.
name: Burke, J.
name: Valenti, S.
name: Tonry, J. L.
name: Denneau, L.
name: Heinze, A. N.
name: Weiland, H.
name: Stalder, B.
name: Vinko, J.
name: Sarneczky, K.
name: Pa, A.
name: Bodi, A.
name: Bognar, Zs.
name: Csak, B.
name: Cseh, B.
name: Csornyei, G.
name: Hanyecz, O.
name: Ignacz, B.
name: Kalup, Cs.
name: Konyves-Toth, R.
name: Kriskovics, L.
name: Ordasi, A.
name: Rajmon, I.
name: Sodor, A.
name: Szabo, R.
name: Szakats, R.
name: Zsidi, G.
name: Williams, S. C.
name: Nordin, J.
name: Cartier, R.
name: Frohmaier, C.
name: Galbany, L.
name: Gutierrez, C. P.
name: Hook, I.
name: Inserra, C.
name: Smith, M.
name: Sand, D. J.
name: Andrews, J. E.
name: Smith, N.
name: Bilinski, C.
Publisher: name: arXiv
Year: 2018
Subjects: subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present an exquisite, 30-min 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 Pan-STARRS1 and 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 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$\pm0.04$ days after explosion, has a FWHM of 3.12$\pm0.04$ days, a blackbody temperature of $T=17,500^{+11,500}_{-9,000}$ K, a peak luminosity of $4.3\pm0.2\times10^{37}\,{\rm erg\,s^{-1}}$, and a total integrated energy of $1.27\pm0.01\times10^{43}\,{\rm erg}$. 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 $\sim$$2\times10^{12}\,{\rm cm}$ 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.
description: 20 pages, 9 figures, 2 tables. Submitted to APJ Letters on 31 Jul 2018, Accepted for publication on 31 Aug 2018