K2 Observations of SN 2018oh Reveal a Two-component Rising Light Curve for a Type Ia Supernova
Authors: Dimitriadis G. , Foley R. J. , Rest A. , Kasen D. , Piro A. L. , Polin A. , Jones D. O. , Villar A. , Narayan G. , A. Coulter D. , Kilpatrick C. D. , Pan Y. -C. , Rojas-Bravo C. , Fox O. D. , Jha S. W. , Nugent P. E. , Riess A. G. , Scolnic D. , Drout M. R. ,   K2 Mission Team, Barentsen G. , Dotson J. , Gully-Santiago M. , Hedges C. , Cody A. M. , Barclay T. , Howell S. ,   KEGS, Garnavich P. , Tucker B. E. , Shaya E. , Mushotzky R. , Olling R. P. , Margheim S. , Zenteno A. ,   Kepler spacecraft team, Coughlin J. , Cleve J. E. Van , de Miranda Cardoso J. Vinícius , Larson K. A. , McCalmont-Everton K. M. , Peterson C. A. , Ross S. E. , Reedy L. H. , 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. ,   Pan-STARRS, Chambers K. C. , Flewelling H. A. , Huber M. E. , Magnier E. A. , Waters C. Z. , Schultz A. S. B. , Bulger J. , Lowe T. B. , Willman M. , Smartt S. J. , Smith K. W. ,   DECam, Points S. , Strampelli G. M. ,   ASAS-SN, Brimacombe J. , Chen P. , Muñoz J. A. , Mutel R. L. , Shields J. , Vallely P. J. , Villanueva S. ,   PTSS/TNTS, Li W. , Wang X. , Zhang J. , Lin H. , Mo J. , Zhao X. , Sai H. , Zhang X. , Zhang K. , Zhang T. , Wang L. , Zhang J. , Baron E. , DerKacy J. M. , Li L. , Chen Z. , Xiang D. , Rui L. , Wang L. , Huang F. , Li X. ,   Las Cumbres Observatory, Hosseinzadeh G. , Howell D. A. , Arcavi I. , Hiramatsu D. , Burke J. , Valenti S. ,   ATLAS, Tonry J. L. , Denneau L. , Heinze A. N. , Weiland H. , Stalder B. ,   Konkoly, Vinkó J. , Sárneczky K. , Pál A. , Bódi A. , Bognár Zs. , Csák B. , Cseh B. , Csörnyei G. , Hanyecz O. , Ignácz B. , Kalup Cs. , Könyves-Tóth R. , Kriskovics L. , Ordasi A. , Rajmon I. , Sódor A. , Szabó R. , Szakáts R. , Zsidi G. ,   ePESSTO, Williams S. C. , Nordin J. , Cartier R. , Frohmaier C. , Galbany L. , Gutiérrez C. P. , Hook I. , Inserra C. , Smith M. ,   University of Arizona, Sand D. J. , Andrews J. E. , Smith N. , Bilinski C. 
Published: December 2018

Abstract
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.