K2 Observations of SN 2018oh Reveal a Two-Component Rising Light Curve for a Type Ia Supernova

G. Dimitriadis , R. J. Foley , A. Rest , D. Kasen , A. L. Piro , A. Polin , D. O. Jones , A. Villar

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G. Narayan D. A. Coulter C. D. Kilpatrick Y. -C. Pan C. Rojas-Bravo O. D. Fox S. W. Jha P. E. Nugent A. G. Riess D. Scolnic M. R. Drout G. Barentsen J. Dotson M. Gully-Santiago C. Hedges A. M. Cody T. Barclay S. Howell P. Garnavich B. E. Tucker E. Shaya R. Mushotzky R. P. Olling S. Margheim A. Zenteno J. Coughlin J. E. Van Cleve J. Vinicius De Miranda Cardoso K. A. Larson K. M. Mccalmont-everton C. A. Peterson S. E. Ross L. H. Reedy D. Osborne C. Mcginn L. Kohnert L. Migliorini A. Wheaton B. Spencer C. Labonde G. Castillo G. Beerman K. Steward M. Hanley R. Larsen R. Gangopadhyay R. Kloetzel T. Weschler V. Nystrom J. Moffatt M. Redick K. Griest M. Packard M. Muszynski J. Kampmeier R. Bjella S. Flynn B. Elsaesser K. C. Chambers H. A. Flewelling M. E. Huber E. A. Magnier C. Z. Waters A. S. B. Schultz J. Bulger T. B. Lowe M. Willman S. J. Smartt K. W. Smith S. Points G. M. Strampelli J. Brimacombe P. Chen J. A. Munoz R. L. Mutel J. Shields P. J. Vallely S. Villanueva Jr W. Li X. Wang J. Zhang H. Lin J. Mo X. Zhao H. Sai X. Zhang K. Zhang T. Zhang L. Wang E. Baron J. M. DerKacy L. Li Z. Chen D. Xiang L. Rui F. Huang X. Li G.Hosseinzadeh D.A.Howell I.Arcavi D.Hiramatsu J.Burke S.Valenti J. L. Tonry L. Denneau A. N. Heinze H. Weiland B. Stalder J. Vinko K. Sarneczky A. Pa A. Bodi Zs. Bognar B. Csak B. Cseh G. Csornyei O. Hanyecz B. Ignacz Cs. Kalup R. Konyves-Toth L. Kriskovics A. Ordasi I. Rajmon A. Sodor R. Szabo R. Szakats G. Zsidi S. C. Williams J. Nordin R. Cartier C. Frohmaier L. Galbany C. P. Gutierrez I. Hook C. Inserra M. Smith D. J. Sand J. E. Andrews N. Smith C. Bilinski

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classification 🌌 astro-ph.HE

keywords curvelightearlyexplosioncompaniondaysfluxobservations

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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.

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K2 Observations of SN 2018oh Reveal a Two-Component Rising Light Curve for a Type Ia Supernova

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