Infant-phase reddening by surface Fe-peak elements in a normal type Ia supernova

Creators: Ni, Yuan Qi; Moon, Dae-Sik; Drout, Maria R.; Polin, Abigail; Sand, David J.; González-Gaitán, Santiago; Kim, Sang Chul; Lee, Youngdae; Park, Hong Soo; Howell, D. Andrew; Nugent, Peter E.; Piro, Anthony L.; Brown, Peter J.; Galbany, Lluís; Burke, Jamison; Hiramatsu, Daichi; Hosseinzadeh, Griffin; Valenti, Stefano; Afsariardchi, Niloufar; Andrews, Jennifer E.; Antoniadis, John; Arcavi, Iair; Beaton, Rachael L.; Bostroem, K. Azalee; Carlberg, Raymond G.; Cenko, S. Bradley; Cha, Sang-Mok; Dong, Yize; Gal-Yam, Avishay; Haislip, Joshua; Holoien, Thomas W.-S.; Johnson, Sean D.; Kouprianov, Vladimir; Lee, Yongseok; Matzner, Christopher D.; Morrell, Nidia; McCully, Curtis; Pignata, Giuliano; Reichart, Daniel E.; Rich, Jeffrey; Ryder, Stuart D.; Smith, Nathan; Wyatt, Samuel; Yang, Sheng

Abstract

Type Ia supernovae are thermonuclear explosions of white dwarf stars. They play a central role in the chemical evolution of the Universe and are an important measure of cosmological distances. However, outstanding questions remain about their origins. Despite extensive efforts to obtain natal information from their earliest signals, observations have thus far failed to identify how the majority of them explode. Here, we present infant-phase detections of SN 2018aoz from a very low brightness of −10.5 AB absolute magnitude, revealing a hitherto unseen plateau in the B band that results in a rapid redward colour evolution between 1.0 and 12.4 hours after the estimated epoch of first light. The missing B-band flux is best explained by line-blanket absorption from Fe-peak elements in the outer 1% of the ejected mass. The observed B − V colour evolution of the supernova also matches the prediction from an over-density of Fe-peak elements in the same outer 1% of the ejected mass, whereas bluer colours are expected from a purely monotonic distribution of Fe-peak elements. The presence of excess nucleosynthetic material in the extreme outer layers of the ejecta points to enhanced surface nuclear burning or extended subsonic mixing processes in some normal type Ia SN explosions.

Additional Information

© 2022 The Author(s), under exclusive licence to Springer Nature Limited. Received 17 August 2021. Accepted 06 January 2022. Published 17 February 2022. This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute (KASI), and the data were obtained at the three host sites of CTIO in Chile, SAAO in South Africa and SSO in Australia. The Gemini South observations were obtained under the K-GMT Science Program (PID GS-2018A-Q-117 and GS-2018B-Q-121) of KASI. The Swift observations were triggered through the Swift GI program 80NSSC19K0316. SOUSA is supported by NASA's Astrophysics Data Analysis Program through grant no. NNX13AF35G. Some of the data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California and NASA. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The Computational HEP program in the United States Department of Energy's Science Office of High Energy Physics provided simulation resources through grant no. KA2401022. This research used resources of the National Energy Research Scientific Computing Center, a Department of Energy Office of Science User Facility operated under contract no. DE-AC02-05CH11231. D.-S.M., M.R.D. and C.D.M. are supported by Discovery Grants from the Natural Sciences and Engineering Research Council of Canada. D.-S.M. was supported in part by a Leading Edge Fund from the Canadian Foundation for Innovation (project no. 30951). M.R.D. was supported in part by the Canada Research Chairs Program, the Canadian Institute for Advanced Research (CIFAR) and the Dunlap Institute at the University of Toronto. D.J.S. acknowledges support by NSF grant nos. AST-1821987, 1821967 and 1908972 and from the Heising–Simons Foundation under grant no. 2020-1864. S.G.-G. acknowledges support by FCT under project CRISP PTDC/FIS-AST-31546 and project UIDB/00099/2020. H.S.P. was supported in part by a National Research Foundation (NRF) of Korea grant funded by the Korean government (MSIT, Ministry of Science and ICT; no. NRF-2019R1F1A1058228). P.J.B. acknowledges support from the Swift GI program 80NSSC19K0316. S.V., Y.D. and K.A.B. acknowledge support by NSF grant nos. AST-1813176 and AST-2008108. C.M. acknowledges support by NSF grant AST-1313484. I.A. is a CIFAR Azrieli Global Scholar in the Gravity and the Extreme Universe Program and acknowledges support from that program, from the Israel Science Foundation (grant nos. 2108/18 and 2752/19), from the United States – Israel Binational Science Foundation (BSF) and from an Israeli Council for Higher Education Alon Fellowship. R.L.B. acknowledges support by NASA through Hubble Fellowship grant no. 51386.01 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA under contract no. NAS 5-26555. A.G.-Y. acknowledges support from the European Union via ERC grant no. 725161, the ISF GW Excellence Center, an IMOS space infrastructure grant and BSF/Transformative and GIF grants, as well as from the Benoziyo Endowment Fund for the Advancement of Science, the Deloro Institute for Advanced Research in Space and Optics, the Veronika A. Rabl Physics Discretionary Fund, P. and T. Gardner, the Yeda-Sela Center for Basic Research and a WIS-CIT joint research grant. A.G.-Y. is the recipient of the Helen and Martin Kimmel Award for Innovative Investigation. L.G. acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033, the European Social Fund (ESF) 'Investing in your future' under the 2019 Ramón y Cajal program RYC2019-027683-I and the PID2020-115253GA-I00 HOSTFLOWS project, as well as from the Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016. G.P. acknowledges support from the Millennium Science Initiative through grant no. IC120009. J.A. is supported by the Stavros Niarchos Foundation (SNF) and the Hellenic Foundation for Research and Innovation (HFRI) under the 2nd Call of 'Science and Society' Action 'Always strive for excellence – Theodoros Papazoglou' (project no. 01431). Data availability: Source data for Fig. 1 during 0–1 days since first light are provided with this paper, whereas data for the entire single-epoch ultraviolet to near-infrared light curves are provided in the Supplementary Information. All photometric and spectroscopic data are also available on the Open Supernova Catalog and WISeREP3. The modelled light curves and spectra of our He-shell DDet simulations are available at https://github.com/niyuanqi/he-shell-ddet. Code availability: We performed light curve template fitting in the post-infant phase using SNooPy, available at https://csp.obs.carnegiescience.edu/data/snpy/snpy. In our He-shell DDet models, hydrodynamics and nucleosynthesis simulations were conducted using Castro and the radiative transfer calculations were conducted using Sedona. The code used to measure the KMTNet light curves of SN 2018aoz, construct the bolometric light curves and generate the analytic ⁵ ⁶Ni-powered light curve models are available at https://github.com/niyuanqi/SNAP. IRAF is distributed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. Contributions: Y.Q.N. conducted most of the analyses under the supervision of D.-S.M. and M.R.D. D.-S.M. is the principal investigator of the KSP that detected the infant-phase features of SN 2018aoz and wrote the KSP pipeline. M.R.D. led the collaboration between the KSP and other partners. Y.Q.N., D.-S.M. and M.R.D. co-drafted the manuscript. A.P. conducted the He-shell DDet simulations under the supervision of P.N. D.-S.M., M.R.D., Y.Q.N., N.A., S.G.-G., S.C.K., Y.L., H.S.P., J.A., A.G.-Y., S.B.C., G.P. and S.D.R. are members of the KSP. N.A., D.-S.M., M.R.D., R.G.C. and C.D.M. are members of the Canadian Gemini South observing programme for the KSP. H.S.P., D.-S.M., S.C.K. and Y.L. are members of the Korean Gemini South observing programme for the KSP. A.L.P. performed the shock breakout modelling. P.J.B. led the Swift program for ultraviolet observations with help from S.B.C. L.G. and G.P. obtained the ANDICAM near-infrared observations. D.J.S. and S.V. co-led the DLT40 programme. J.H., D.E.R., V.K. and S.W. contributed to the operation of the DLT40 programme. S.Y. built the machine-learning implementation for the DLT40 survey. K.A.B., Y.D., J.E.A. and N.S. are members of the DLT40 team who obtained the Keck and MMT spectra. S.-M.C. and Y.L. helped operate the KMTNet. D.A.H., C.M., I.A., J.B., D.H. and G.H. contributed to the LCO photometry and the FLOYDS spectroscopy. M.R.D., R.L.B., T.W.-S.H., S.D.J., N.M. and J.R. contributed to the du Pont WFCCD and Magellan spectra. All of the authors contributed to the discussion. The authors declare no competing interests. Peer review information: Nature Astronomy thanks Ji-an Jiang and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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