Nearby Supernova Factory Observations of SN 2007if: First Total Mass Measurement of a Super-Chandrasekhar-Mass Progenitor

• Published in: The Astrophysical journal Vol. 713; no. 2; pp. 1073 - 1094
• Main Authors: Scalzo, R. A, Aldering, G, Antilogus, P, Aragon, C, Bailey, S, Baltay, C, Bongard, S, Buton, C, Childress, M, Chotard, N, Copin, Y, Fakhouri, H. K, Gal-Yam, A, Gangler, E, Hoyer, S, Kasliwal, M, Loken, S, Nugent, P, Pain, R, Pécontal, E, Pereira, R, Perlmutter, S, Rabinowitz, D, Rau, A, Rigaudier, G, Runge, K, Smadja, G, Tao, C, Thomas, R. C, Weaver, B, Wu, C
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 20-04-2010; IOP; American Astronomical Society
• Subjects: Astronomy; Astrophysics; Earth, ocean, space; Exact sciences and technology; High Energy Astrophysical Phenomena; Physics; Sciences of the Universe; Mass measurement; supernovae: individual (SNe 2003fg, 2006gz, 2007if, 2009dc); White dwarf stars; white dwarfs; Supernovae; supernovae: general
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/713/2/1073

We present photometric and spectroscopic observations of SN 2007if, an overluminous (M_V = -20.4), red (B-V = 0.16 at B-band maximum), slow-rising (t_rise = 24 days) type Ia supernova in a very faint (M_g = -14.10) host galaxy. A spectrum at 5 days past B-band maximum light is a direct match to the super-Chandrasekhar-mass candidate SN Ia 2003fg, showing Si II and C II at ~9000 km/s. A high signal-to-noise co-addition of the SN spectral time series reveals no Na I D absorption, suggesting negligible reddening in the host galaxy, and the late-time color evolution has the same slope as the Lira relation for normal SNe Ia. The ejecta appear to be well mixed, with no strong maximum in I-band and a diversity of iron-peak lines appearing in near-maximum-light spectra. SN2007 if also displays a plateau in the Si II velocity extending as late as +10 days, which we interpret as evidence for an overdense shell in the SN ejecta. We calculate the bolometric light curve of the SN and use it and the \ion{Si}{2} velocity evolution to constrain the mass of the shell and the underlying SN ejecta, and demonstrate that SN2007 if is strongly inconsistent with a Chandrasekhar-mass scenario. Within the context of a "tamped detonation" model appropriate for double-degenerate mergers, and assuming no host extinction, we estimate the total mass of the system to be 2.4 +/- 0.2 solar masses, with 1.6 +/- 0.1 solar masses of nickel-56 and with 0.3-0.5 solar masses in the form of an envelope of unburned carbon/oxygen. Our modeling demonstrates that the kinematics of shell entrainment provide a more efficient mechanism than incomplete nuclear burning for producing the low velocities typical of super-Chandrasekhar-mass SNeIa.