Astron. J., 138, 376-391 (2009/August-0)
SN 2008ha: an extremely low luminosity and exceptionally low energy supernova.
FOLEY R.J., CHORNOCK R., FILIPPENKO A.V., GANESHALINGAM M., KIRSHNER R.P., LI W., CENKO S.B., CHALLIS P.J., FRIEDMAN A.S., MODJAZ M., SILVERMAN J.M. and WOOD-VASEY W.M.
Abstract (from CDS):
We present ultraviolet, optical, and near-infrared photometry as well as optical spectra of the peculiar supernova (SN) 2008ha. SN 2008ha had a very low peak luminosity, reaching only MV= -14.2 mag, and low line velocities of only ∼2000 km/s near maximum brightness, indicating a very small kinetic energy per unit mass of ejecta. Spectroscopically, SN 2008ha is a member of the SN 2002cx-like class of SNe, a peculiar subclass of SNe Ia; however, SN 2008ha is the most extreme member, being significantly fainter and having lower line velocities than the typical member, which is already ∼2 mag fainter and has line velocities ∼5000 km/s smaller (near maximum brightness) than a normal SN Ia. SN 2008ha had a remarkably short rise time of only ∼10 days, significantly shorter than either SN 2002cx-like objects (∼15 days) or normal SNe Ia (∼19.5 days). The bolometric light curve of SN 2008ha indicates that SN 2008ha peaked at Lpeak= (9.5±1.4)x1040 erg/s, making SN 2008ha perhaps the least luminous SN ever observed. From its peak luminosity and rise time, we infer that SN 2008ha generated (3.0±0.9)x10–3 M☉ of 56Ni, had a kinetic energy of ∼2x1048 erg, and ejected 0.15 M☉ of material. The host galaxy of SN 2008ha has a luminosity, star formation rate, and metallicity similar to those of the Large magellanic Cloud. We classify three new (and one potential) members of the SN 2002cx-like class, expanding the sample to 14 (and one potential) members. The host-galaxy morphology distribution of the class is consistent with that of SNe Ia, Ib, Ic, and II. Several models for generating low-luminosity SNe can explain the observations of SN 2008ha; however, if a single model is to describe all SN 2002cx-like objects, deflagration of carbon-oxygen white dwarfs, with SN 2008ha being a partial deflagration and not unbinding the progenitor star, is preferred. The rate of SN 2008ha-like events is ∼10% of the SN Ia rate, and in the upcoming era of transient surveys, several thousand similar objects may be discovered, suggesting that SN 2008ha may be the tip of a low-luminosity transient iceberg.
galaxies: individual: UGC 12682 - supernovae: general - supernovae: individual (SN 1991bj, SN 2002cx, SN 2004gw, SN 2006hn, SN 2007J, SN 2008ha)
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