NEBULAR SPECTRA AND EXPLOSION ASYMMETRY OF TYPE Ia SUPERNOVAE

Journal Article · Sat Jan 09 23:00:00 EST 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/708/2/1703· OSTI ID:21392403

Maeda, K; Nomoto, K ^[1]; Taubenberger, S; Mazzali, P A ^[2]; Sollerman, J ^[3]; Leloudas, G ^[4]; Motohara, K ^[5]

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1. Institute for the Physics and Mathematics of the Universe (IPMU), University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8568 (Japan)
2. Max-Planck-Institut fuer Astrophysik, Karl-Schwarzschild-Strasse 1, 85741 Garching (Germany)
3. Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm (Sweden)
4. Dark Cosmology Centre, Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen (Denmark)
5. Institute of Astronomy, Graduate School of Science, University of Tokyo, Mitaka, Tokyo 181-0015 (Japan)

The spectral signatures of asymmetry in Type Ia Supernova (SN Ia) explosions are investigated, using a sample of late-time nebular spectra. First, a kinematical model is constructed for SN Ia 2003hv, which can account for the main features in its optical, Near-Infrared (NIR), and Mid-Infrared (Mid-IR) late-time spectra. It is found that an asymmetric off-center model can explain the observed characteristics of SN 2003hv. This model includes a relatively high-density, Fe-rich region which displays a large velocity off-set, and a relatively low density, extended {sup 56}Ni-rich region which is more spherically distributed. The high-density region consists of the inner stable Fe-Ni region and outer {sup 56}Ni-rich region. Such a distribution may be the result of a delayed-detonation explosion, in which the first deflagration produces the global asymmetry in the innermost ejecta, while the subsequent detonation can lead to the bulk spherical symmetry. This configuration, if viewed from the direction of the off-set, can consistently explain the blueshift in some of the emission lines and virtually no observed shift in other lines in SN 2003hv. For this model, we then explore the effects of different viewing angles and the implications for SNe Ia in general. The model predicts that a variation of the central wavelength, depending on the viewing angle, should be seen in some lines (e.g., [Ni II] lambda7378), while the strongest lines (e.g., [Fe III] blend at approx4700 A) will not show this effect. By examining optical nebular spectra of 12 SNe Ia, we have found that such a variation indeed exists. We suggest that the global asymmetry in the innermost ejecta, as likely imprint of the deflagration flame propagation, is a generic feature of SNe Ia. It is also shown that various forbidden lines in the NIR and Mid-IR regimes provide strong diagnostics to further constrain the explosion geometry and thus the explosion mechanism.

• OSTI ID: 21392403
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 708; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

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79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
BETA DECAY RADIOISOTOPES
BETA-PLUS DECAY RADIOISOTOPES
BINARY STARS
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
EMISSION
ENERGY TRANSFER
ERUPTIVE VARIABLE STARS
EVEN-EVEN NUCLEI
EXPLOSIONS
FLAME PROPAGATION
HEAT TRANSFER
INTERMEDIATE MASS NUCLEI
ISOTOPES
NICKEL 56
NICKEL ISOTOPES
NUCLEAR REACTIONS
NUCLEI
NUCLEOSYNTHESIS
RADIANT HEAT TRANSFER
RADIOISOTOPES
STARS
SUPERNOVAE
SYNTHESIS
VARIABLE STARS