OISTER OPTICAL and NEAR-INFRARED OBSERVATIONS of TYPE IAX SUPERNOVA 2012Z

We report observations of the Type Iax supernova (SN Iax) 2012Z at optical and near-infrared (NIR) wavelengths from immediately after the explosion until ∼260 days after the maximum luminosity using the Optical and Infrared Synergetic Telescopes for Education and Research Target-of-Opportunity program and the Subaru Telescope. We found that the NIR light curve evolutions and color evolutions are similar to those of SNe Iax 2005hk and 2008ha. The NIR absolute magnitudes (M_J ∼ -18.1 mag and M_H ∼ -18.3 mag) and the rate of decline of the light curve (Δm₁₅(B) = 1.6 ± 0.1 mag) are very similar to those of SN 2005hk (M_J ∼ -17.7 mag, M_H ∼ -18.0 mag, and Δ m₁₅(B) ∼ 1.6 mag), yet differ significantly from SNe 2008ha and 2010ae (M_J ∼ -14 to -15 mag and Δm₁₅(B) ∼ 2.4-2.7 mag). The estimated rise time is 12.0 ± 3.0 days, which is significantly shorter than that of SN 2005hk or any other SNe Ia. The rapid rise indicates that the ⁵⁶Ni distribution may extend into the outer layer or that the effective opacity may be lower than that in normal SNe Ia. The late-phase spectrum exhibits broader emission lines than those of SN 2005hk by a factor of six to eight. Such high velocities of the emission lines indicate that the density profile of the inner ejecta extends more than that of SN 2005hk. We argue that the most favored explosion scenario is a "failed deflagration" model, although the pulsational delayed detonations is not excluded.