SN 2000cx and SN 2013bh: extremely rare, nearly twin Type Ia supernovae

Creators: Silverman, Jeffrey M.; Vinko, Jozsef; Kasliwal, Mansi M.; Fox, Ori D.; Cao, Yi; Johansson, Joel; Perley, Daniel A.; Tal, David; Wheeler, J. Craig; Amanullah, Rahman; Arcavi, Iair; Bloom, Joshua S.; Gal-Yam, Avishay; Goobar, Ariel; Kulkarni, Shrinivas R.; Laher, Russ; Lee, William H.; Marion, G. H.; Nugent, Peter E.; Shivvers, Isaac

Abstract

The Type Ia supernova (SN Ia) SN 2000cx was one of the most peculiar transients ever discovered, with a rise to maximum brightness typical of a SN Ia, but a slower decline and a higher photospheric temperature. 13 yr later SN 2013bh (also known as iPTF13abc), a near identical twin, was discovered and we obtained optical and near-infrared photometry and low-resolution optical spectroscopy from discovery until about 1 month past r-band maximum brightness. The spectra of both objects show iron-group elements [Co II, Ni II, Fe II, Fe III and high-velocity features (HVFs) of Ti II], intermediate-mass elements (Si II, Si III and S II) and separate normal velocity features (∼12 000 km s^(−1)) and HVFs (∼24 000 km s^(−1)) of Ca II. Persistent absorption from Fe III and Si III, along with the colour evolution, implies high blackbody temperatures for SNe 2013bh and 2000cx (∼12 000 K). Both objects lack narrow Na I D absorption and exploded in the outskirts of their hosts, indicating that the SN environments were relatively free of interstellar or circumstellar material and may imply that the progenitors came from a relatively old and low-metallicity stellar population. Models of SN 2000cx, seemingly applicable to SN 2013bh, imply the production of up to ∼1 M_⊙ of ^(56)Ni and (4.3–5.5) × 10^(−3) M_⊙ of fast-moving Ca ejecta.

Additional Information

© 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. First published online: September 24, 2013. Accepted 2013 August 29. Received 2013 August 8; in original form 2013 July 12. We would like to thank M. Ganeshalingam, P. Kelly and E. Ofek for helpful discussions, J. Caldwell, S. Odewahn and S. Rostopchin for their assistance with some of the observations, as well as the PESSTO and CRTS collaborations for making some of their data on SN 2013bh publicly available. The HET is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximilians-Universität München and Georg-August-Universität Göttingen. The HET is named in honour of its principal benefactors, William P. Hobby and Robert E. Eberly. The Marcario Low Resolution Spectrograph is named for Mike Marcario of High Lonesome Optics who fabricated several optics for the instrument but died before its completion. The LRS is a joint project of the HET partnership and the Instituto de Astronomía de la Universidad Nacional Autόnoma de México. Some of the data presented herein 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 the National Aeronautics and Space Administration (NASA); the observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community; we are most fortunate to have the opportunity to conduct observations from this mountain. This work is partially based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. We thank the RATIR instrument team and the staff of the Observatorio Astronόmico Nacional on Sierra San Pedro Mártir. RATIR is a collaboration between the University of California, the Universidad Nacional Autonόma de México, NASA Goddard Space Flight Center and Arizona State University, benefiting from the loan of an H2RG detector from Teledyne Scientific and Imaging. RATIR, the automation of the Harold L. Johnson Telescope of the Observatorio Astronόmico Nacional on Sierra San Pedro Mártir and the operation of both are funded by the partner institutions and through NASA grants NNX09AH71G, NNX09AT02G, NNX10AI27G and NNX12AE66G, CONACyT grants INFR-2009-01-122785, UNAM PAPIIT grant IN113810 and a UC MEXUS-CONACyT grant. The National Energy Research Scientific Computing Center, supported by the Office of Science of the US Department of Energy, provided staff, computational resources and data storage for this project. This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the NSF and the US Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/. JMS is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1302771. JV is supported by Hungarian OTKA Grant NN 107637. MMK acknowledges generous support from the Hubble Fellowship and Carnegie-Princeton Fellowship. JCW's supernova group at UT Austin is supported by NSF Grant AST 11-09801. Some work on this paper by JCW was done in the hospitable clime of the Aspen Center for Physics that is supported by NSF Grant PHY-1066293. JSB acknowledges the generous support of a CDI grant (#0941742) from the National Science Foundation.

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Submitted - 1307.3555v2.pdf

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