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 M _ { V } = -14.2 mag , and low line velocities of only \sim 2000 km s ^ { -1 } 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 \sim 2 mag fainter and has line velocities \sim 5000 km s ^ { -1 } smaller ( near maximum brightness ) than a normal SN Ia .
SN 2008ha had a remarkably short rise time of only \sim 10 days , significantly shorter than either SN 2002cx-like objects ( \sim 15 days ) or normal SNe Ia ( \sim 19.5 days ) .
The bolometric light curve of SN 2008ha indicates that SN 2008ha peaked at L _ { peak } = ( 9.5 \pm 1.4 ) \times 10 ^ { 40 } ergs s ^ { -1 } , 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 \pm 0.9 ) \times 10 ^ { -3 } M _ { \sun } of ^ { 56 } Ni , had a kinetic energy of \sim 2 \times 10 ^ { 48 } ergs , and ejected 0.15 M _ { \sun } 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 , either electron capture in Ne-Mg white dwarfs causing a core collapse , or deflagration of C-O white dwarfs with SN 2008ha being a partial deflagration and not unbinding the progenitor star , are preferred .
The rate of SN 2008ha-like events is \sim 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 .