Dimitriadis, G. and Foley, R. J. and Rest, A. and Kasen, D. and Piro, A. L. and Polin, A. and Jones, D. O. and Villar, A. and Narayan, G. and Coulter, D. A. and Kilpatrick, C. D. and Pan, Y.-C. and Rojas-Bravo, C. and Fox, O. D. and Jha, S. W. and Nugent, P. E. and Riess, A. G. and Scolnic, D. and Drout, M. R. and Barentsen, G. and Dotson, J. and Gully-Santiago, M. and Hedges, C. and Cody, A. M. and Barclay, T. and Howell, S. and Garnavich, P. and Tucker, B. E. and Shaya, E. and Mushotzky, R. and Olling, R. P. and Margheim, S. and Zenteno, A. and Coughlin, J. and Van Cleve, J. E. and Cardoso, J. Vinicius de Miranda and Larson, K. A. and McCalmont-Everton, K. M. and Peterson, C. A. and Ross, S. E. and Reedy, L. H. and Osborne, D. and McGinn, C. and Kohnert, L. and Migliorini, L. and Wheaton, A. and Spencer, B. and Labonde, C. and Castillo, G. and Beerman, G. and Steward, K. and Hanley, M. and Larsen, R. and Gangopadhyay, R. and Kloetzel, R. and Weschler, T. and Nystrom, V. and Moffatt, J. and Redick, M. and Griest, K. and Packard, M. and Muszynski, M. and Kampmeier, J. and Bjella, R. and Flynn, S. and Elsaesser, B. and Chambers, K. C. and Flewelling, H. A. and Huber, M. E. and Magnier, E. A. and Waters, C. Z. and Schultz, A. S. B. and Bulger, J. and Lowe, T. B. and Willman, M. and Smartt, S. J. and Smith, K. W. and Points, S. and Strampelli, G. M. and Brimacombe, J. and Chen, P. and Munoz, J. A. and Mutel, R. L. and Shields, J. and Vallely, P. J. and Villanueva, S., Jr and Li, W. and Wang, X. and Zhang, J. and Lin, H. and Mo, J. and Zhao, X. and Sai, H. and Zhang, X. and Zhang, K. and Zhang, T. and Wang, L. and Zhang, J. and Baron, E. and DerKacy, J. M. and Li, L. and Chen, Z. and Xiang, D. and Rui, L. and Wang, L. and Huang, F. and Li, X. and Hosseinzadeh, G. and Howell, D. A. and Arcavi, I. and Hiramatsu, D. and Burke, J. and Valenti, S. and Tonry, J. L. and Denneau, L. and Heinze, A. N. and Weiland, H. and Stalder, B. and Vinko, J. and Sarneczky, K. and Pa, A. and Bodi, A. and Bognar, Zs. and Csak, B. and Cseh, B. and Csornyei, G. and Hanyecz, O. and Ignacz, B. and Kalup, Cs. and Konyves-Toth, R. and Kriskovics, L. and Ordasi, A. and Rajmon, I. and Sodor, A. and Szabo, R. and Szakats, R. and Zsidi, G. and Williams, S. C. and Nordin, J. and Cartier, R. and Frohmaier, C. and Galbany, L. and Gutierrez, C. P. and Hook, I. and Inserra, C. and Smith, M. and Sand, D. J. and Andrews, J. E. and Smith, N. and Bilinski, C. (2019) K2 Observations of SN 2018oh Reveal a Two-Component Rising Light Curve for a Type Ia Supernova. Astrophysical Journal Letters, 870. ISSN 2041-8205
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Abstract
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.