Absence of Fast-moving Iron in an Intermediate Type Ia Supernova between Normal and Super-Chandrasekhar

Creators: Cao, Yi; Johansson, J.; Nugent, Peter E.; Goobar, A.; Nordin, Jakob; Kulkarni, S. R.; Cenko, S. Bradley; Fox, Ori; Kasliwal, Mansi M.; Fremling, C.; Amanullah, R.; Hsiao, E. Y.; Perley, D. A.; Bue, Brian D.; Masci, Frank J.; Lee, William H.; Chotard, Nicolas

Abstract

In this paper, we report observations of a peculiar SN Ia iPTF13asv (a.k.a., SN2013cv) from the onset of the explosion to months after its peak. The early-phase spectra of iPTF13asv show an absence of iron absorption, indicating that synthesized iron elements are confined to low-velocity regions of the ejecta, which, in turn, implies a stratified ejecta structure along the line of sight. Our analysis of iPTF13asv's light curves and spectra shows that it is an intermediate case between normal and super-Chandrasekhar events. On the one hand, its light curve shape (B-band Δm_(15) = 1.03 ± 0.01) and overall spectral features resemble those of normal SNe Ia. On the other hand, its large peak optical and UV luminosity (M_B = -19.84 mag, M_(uvm2) = -15.5 mag) and its low but almost constant Si II velocities of about 10,000 km s^(−1) are similar to those in super-Chandrasekhar events, and its persistent carbon signatures in the spectra are weaker than those seen commonly in super-Chandrasekhar events. We estimate a ^(56)Ni mass of 0.81 ± ^(+0.10)_(-0.18) M⊙ and a total ejecta mass of 1.59^(+0.45)_(-0.12)M⊙. The large ejecta mass of iPTF13asv and its stratified ejecta structure together seemingly favor a double-degenerate origin.

Additional Information

© 2016 The American Astronomical Society. Received 2016 January 4; accepted 2016 April 10; published 2016 June 1. This research is partly supported by the Swift Guest Investigator program and by the National Science Foundation. Y.C. and M.M.K. acknowledge support from the National Science Foundation PIRE program grant 1545949. A.G. and R.A. acknowledge support from the Swedish Research Council and the Swedish Space Board. E.Y.H. acknowledges the support provided by the Danish Agency for Science and Technology and Innovation through a Sapere Aude Level 2 grant. Some observations were obtained with the SuperNova Integral Field Spectrograph on the University of Hawaii 2.2 m telescope as part of the Nearby Supernova Factory II project, a scientific collaboration between the Centre de Recherche Astronomique de Lyon, Institut de Physique Nucl'eaire de Lyon, Laboratoire de Physique Nucl'eaire et des Hautes Energies, Lawrence Berkeley National Laboratory, Yale University, University of Bonn, Max Planck Institute for Astrophysics, Tsinghua Center for Astrophysics, and Centre de Physique des Particules de Marseille. Some data in this paper were obtained with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOTSA. We also thank the RATIR project team and the staff of the Observatorio Astronómico Nacional on Sierra San Pedro Mártir. RATIR is a collaboration between the University of California, the Universidad Nacional Autónoma de México, NASA Goddard Space Flight Center, and Arizona State University, benefiting from the loan of an H2RG detector and hardware and software support from Teledyne Scientific and Imaging. RATIR, the automation of the Harold L. Johnson Telescope of the Observatorio Astronómico Nacional on Sierra San Pedro Mártir and the operation of both is funded through NASA grants NNX09AH71G, NNX09AT02G, NNX10AI27G, and NNX12AE66G, CONACyT grants LN 260369, and UNAM PAPIIT grant IG100414. A portion of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2016 California Institute of Technology. All Rights Reserved. US Government Support Acknowledged.

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