Early Observations of the Type Ia Supernova iPTF 16abc: A Case of Interaction with Nearby, Unbound Material and/or Strong Ejecta Mixing

Creators: Miller, A. A.; Cao, Y.; Piro, A. L.; Blagorodnova, N.; Bue, B. D.; Cenko, S. B.; Dhawan, S.; Ferretti, R.; Fox, O. D.; Fremling, C.; Goobar, A.; Howell, D. A.; Hosseinzadeh, G.; Kasliwal, M. M.; Laher, R. R.; Lunnan, R.; Masci, F. J.; McCully, C.; Nugent, P. E.; Sollerman, J.; Taddia, F.; Kulkarni, S. R.

Abstract

Early observations of Type Ia supernovae (SNe Ia) provide a unique probe of their progenitor systems and explosion physics. Here we report the intermediate Palomar Transient Factory (iPTF) discovery of an extraordinarily young SN Ia, iPTF 16abc. By fitting a power law to our early light curve, we infer that first light for the SN, that is, when the SN could have first been detected by our survey, occurred only 0.15 ±_(0.07)^(0.15) days before our first detection. In the ~24 hr after discovery, iPTF 16abc rose by ~2 mag, featuring a near-linear rise in flux for ≳3 days. Early spectra show strong C ii absorption, which disappears after ~7 days. Unlike the extensively observed Type Ia SN 2011fe, the (B-V)_0 colors of iPTF 16abc are blue and nearly constant in the days after explosion. We show that our early observations of iPTF 16abc cannot be explained by either SN shock breakout and the associated, subsequent cooling or the SN ejecta colliding with a stellar companion. Instead, we argue that the early characteristics of iPTF 16abc, including (i) the rapid, near-linear rise, (ii) the nonevolving blue colors, and (iii) the strong C ii absorption, are the result of either ejecta interaction with nearby, unbound material or vigorous mixing of radioactive ^(56)Ni in the SN ejecta, or a combination of the two. In the next few years, dozens of very young normal SNe Ia will be discovered, and observations similar to those presented here will constrain the white dwarf explosion mechanism.

Additional Information

© 2018 The American Astronomical Society. Received 2017 August 23. Accepted 2017 December 5. Published 2018 January 11. This study has benefited from the suggestions of an anonymous referee. We are deeply grateful to R. C. Thomas for indulging a slew of questions regarding C ii in SNe. Similarly, it is our pleasure to buy a beer for R. Amanullah and U. Feindt for discussions regarding SALT2. This paper utilizes the LCO infrastructure for rapid and regular monitoring of SNe, and we thank S. Valenti and I. Arcavi for their development efforts. Figure 3 would not have been possible without S. Blondin generously sharing the data from Blondin et al. (2012). Much of the analysis presented herein would not have been possible without the help of several observers. We thank M. West for taking the first spectrum of iPTF 16abc as a ToO on the DCT. We also thank P. GuhaThakurta, E. C. Cunningham, K. A. Plant, H. Jang, and J. Torres for executing a Keck ToO as part of the UC/Caltech partnership, and also the Gemini service observers for executing our ToO observations. Additionally, J. Cohen, N. Suzuki, V. Ravi, R. Walters, A. Ho, H. Vedanthamand, K. De, and L. Yan helped obtain data for this paper. A.A.M. is funded by the Large Synoptic Survey Telescope Corporation in support of the Data Science Fellowship Program. Y.C. acknowledges support from a postdoctoral fellowship at the eScience Institute, University of Washington. D.A.H., C.M., and G.H. are supported by NSF-1313484. The Intermediate Palomar Transient Factory project is a scientific collaboration among the California Institute of Technology, Los Alamos National Laboratory, the University of Wisconsin, Milwaukee, the Oskar Klein Center, the Weizmann Institute of Science, the TANGO Program of the University System of Taiwan, and the Kavli Institute for the Physics and Mathematics of the Universe. This work was supported by the GROWTH project funded by the National Science Foundation under grant no. 1545949. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This work makes use of observations from the LCO network. These results made use of the Discovery Channel Telescope at Lowell Observatory. Lowell is a private, nonprofit institution dedicated to astrophysical research and public appreciation of astronomy and operates the DCT in partnership with Boston University, the University of Maryland, the University of Toledo, Northern Arizona University, and Yale University. The upgrade of the DeVeny optical spectrograph has been funded by a generous grant from John and Ginger Giovale. Based on observations made with the Nordic Optical Telescope, operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofísica de Canarias. Facilities: DCT - , Gemini:Gillett - , Hale - , Keck:I - , Keck:II - , LCOGT - , PO:1.2m - , PO:1.5m - , NOT - , VLT - , Swift - , OANSPM:HJT - .

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