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Published June 2015 | Published + Submitted
Journal Article Open

Strong near-infrared carbon in the Type Ia supernova iPTF13ebh

Abstract

We present near-infrared (NIR) time-series spectroscopy, as well as complementary ultraviolet (UV), optical, and NIR data, of the Type Ia supernova (SN Ia) iPTF13ebh, which was discovered within two days from the estimated time of explosion. The first NIR spectrum was taken merely 2.3 days after explosion and may be the earliest NIR spectrum yet obtained of a SN Ia. The most striking features in the spectrum are several NIR C i lines, and the C iλ1.0693 μm line is the strongest ever observed in a SN Ia. Interestingly, no strong optical C ii counterparts were found, even though the optical spectroscopic time series began early and is densely cadenced. Except at the very early epochs, within a few days from the time of explosion, we show that the strong NIR C i compared to the weaker optical C ii appears to be general in SNe Ia. iPTF13ebh is a fast decliner with Δm15(B) = 1.79 ± 0.01, and its absolute magnitude obeys the linear part of the width-luminosity relation. It is therefore categorized as a "transitional" event, on the fast-declining end of normal SNe Ia as opposed to subluminous/91bg-like objects. iPTF13ebh shows NIR spectroscopic properties that are distinct from both the normal and subluminous/91bg-like classes, bridging the observed characteristics of the two classes. These NIR observations suggest that composition and density of the inner core are similar to that of 91bg-like events, and that it has a deep-reaching carbon burning layer that is not observed in more slowly declining SNe Ia. There is also a substantial difference between the explosion times inferred from the early-time light curve and the velocity evolution of the Si iiλ0.6355 μm line, implying a long dark phase of ~4 days.

Additional Information

© 2015 ESO. Article published by EDP Sciences. Received 7 November 2014; Accepted 7 March 2015; Published online 22 May 2015. This paper includes data gathered with the 6.5-m Magellan Telescopes located at Las Campanas Observatory, Chile. This paper is based upon work supported by the National Science Foundation under Grant No. AST-1008343. M.S., E.Y.H., C.C, and C.G. acknowledge the generous support provided by the Danish Agency for Science and Technology and Innovation through a Sapere Aude Level 2 grant. S.G. acknowledges support from CONICYT through FONDECYT grant 3130680 and from the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC12009, awarded to The Millennium Institute of Astrophysics, MAS. The Dark Cosmology Centre is funded by the Danish National Research Foundation. LANL participation in iPTF is supported by the US Department of Energy as part of the Laboratory Directed Research and Development program. The bulk of the data presented here was obtained with the 1 m Swope, 2.5 m du Pont, and the 6.5 m Magellan Telescopes at the Las Campanas Observatory. This work also relies on data obtained at the Gemini Observatory, under the long-term program GN-2013B-Q-76. The Gemini Observatory is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), the National Research Council (Canada), CONICYT (Chile), the Australian Research Council (Australia), Ministério da Ciência, Tecnologia e Inovação (Brazil) and Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina). The authors would like to recognize the very significant cultural role and reverence that the summit of Mauna Kea has within the indigenous community of Hawaii. We are grateful for our opportunity to conduct observations from this mountain. We have also made use of the Nordic Optical Telescope, which is operated by the Nordic Optical Telescope Scientific Association at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. The William Herschel Telescope and its override programme are operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. This research used resources from the National Energy Research Scientific Computing Center (NERSC), which is supported by the Office Science of the US Department of Energy under Contract No. DEAC02-05CH11231. We have also made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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August 20, 2023
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