Journal
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Volume 410, Issue 1, Pages 585-611Publisher
OXFORD UNIV PRESS
DOI: 10.1111/j.1365-2966.2010.17474.x
Keywords
supernovae: general; supernovae: individual: SN 2009dc; supernovae: individual: SN 2007if; supernovae: individual: SN 2003fg; supernovae: individual: SN 2006gz
Categories
Funding
- W. M. Keck Foundation
- NSF [AST-0908886]
- DOE [DE-FC02-06ER41453, DE-FG02-08ER41563]
- NASA [NNX09AL08G]
- TABASGO Foundation
- Marc J. Staley for a Graduate Fellowship
- Sun Microsystems, Inc.
- Hewlett-Packard Company
- AutoScope Corporation
- Lick Observatory
- University of California
- Sylvia & Jim Katzman Foundation
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In this paper, we present and analyse optical photometry and spectra of the extremely luminous and slowly evolving Type Ia supernova (SN Ia) 2009dc, and offer evidence that it is a super-Chandrasekhar mass (SC) SN Ia and thus has a SC white dwarf (WD) progenitor. Optical spectra of SN 2007if, a similar object, are also shown. SN 2009dc had one of the most slowly evolving light curves ever observed for a SN Ia, with a rise time of similar to 23 d and delta m(15)(B) = 0.72 mag. We calculate a lower limit to the peak bolometric luminosity of similar to 2.4 x 1043 erg s-1, though the actual value is likely almost 40 per cent larger. Optical spectra of SN 2009dc and SN 2007if obtained near maximum brightness exhibit strong C ii features (indicative of a significant amount of unburned material), and the post-maximum spectra are dominated by iron-group elements (IGEs). All of our spectra of SN 2009dc and SN 2007if also show low expansion velocities. However, we see no strong evidence in SN 2009dc for a velocity 'plateau' near maximum light like the one seen in SN 2007if. The high luminosity and low expansion velocities of SN 2009dc lead us to derive a possible WD progenitor mass of more than 2 M-circle dot and a 56Ni mass of about 1.4-1.7 M-circle dot. We propose that the host galaxy of SN 2009dc underwent a gravitational interaction with a neighbouring galaxy in the relatively recent past. This may have led to a sudden burst of star formation which could have produced the SC WD progenitor of SN 2009dc and likely turned the neighbouring galaxy into a 'post-starburst galaxy'. No published model seems to match the extreme values observed in SN 2009dc, but simulations do show that such massive progenitors can exist (likely as a result of the merger of two WDs) and can possibly explode as SC SNe Ia.
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