We report observations of the Type Iax supernova (SN Iax) 2012Z at optical and near-infrared wavelengths from immediately after the explosion until $sim$ $260$ days after the maximum luminosity using the Optical and Infrared Synergetic Telescopes for
Education and Research (OISTER) Target-of-Opportunity (ToO) program and the Subaru telescope. We found that the near-infrared (NIR) light curve evolutions and color evolutions are similar to those of SNe Iax 2005hk and 2008ha. The NIR absolute magnitudes ($M_{J}sim-18.1$ mag and $M_{H}sim-18.3$ mag) and the rate of decline of the light curve ($Delta$ $m_{15}$($B$)$=1.6 pm 0.1$ mag) are very similar to those of SN 2005hk ($M_{J}sim-17.7$ mag, $M_{H}sim$$-18.0$ mag, and $Delta$ $m_{15}$($B$)$sim1.6$ mag), yet differ significantly from SNe 2008ha and 2010ae ($M_{J}sim-14 - -15$ mag and $Delta$ $m_{15}$($B$)$sim2.4-2.7$ mag). The estimated rise time is $12.0 pm 3.0$ days, which is significantly shorter than that of SN 2005hk or any other Ia SNe. The rapid rise indicates that the $^{56}$Ni 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 6--8. 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.
We report photometric and spectroscopic observations of the nearby Type Ia Supernova (SN Ia) 2012ht from $-15.8$ days to $+49.1$ days after $B$-band maximum. The decline rate of the light curve is $Delta m_{15}$($B$)$=1.39~pm~0.05$ mag, which is inte
rmediate between normal and subluminous SNe Ia, and similar to that of the `transitional Type Ia SN 2004eo. The spectral line profiles also closely resemble those of SN 2004eo. We were able to observe SN 2012ht at very early phase, when it was still rising and was about three magnitudes fainter than at the peak. The rise time to the $B$-band maximum is estimated to be $17.6 pm 0.5$ days and the time of the explosion is MJD $56277.98 pm 0.13$. SN 2012ht is the first transitional SN Ia whose rise time is directly measured without using light curve templates, and the fifth SN Ia overall. This rise time is consistent with those of the other four SNe within the measurement error, even including the extremely early detection of SN 2013dy. The rising part of the light curve can be fitted by a quadratic function, and shows no sign of a shock-heating component due to the interaction of the ejecta with a companion star. The rise time is significantly longer than that inferred for subluminous SNe such as SN 1991bg, which suggests that a progenitor and/or explosion mechanism of transitional SNe Ia are more similar to normal SNe Ia rather than subluminous SNe Ia.
We present early spectroscopy of the recurrent nova U~Sco during the outburst in 2010. We successfully obtained time-series spectra at $t_{rm d}=$0.37--0.44~d, where $t_{rm d}$ denotes the time from the discovery of the present outburst. This is the
first time-resolved spectroscopy on the first night of U Sco outbursts. At $t_{rm d}sim 0.4$~d the H$alpha$ line consists of a blue-shifted ($-5000$ km s$^{-1}$) narrow absorption component and a wide emission component having triple peaks, a blue ($sim -3000$ km s$^{-1}$), a central ($sim 0$ km s$^{-1}$) and a red ($sim +3000$ km s$^{-1}$) ones. The blue and red peaks developed more rapidly than the central one during the first night. This rapid variation would be caused by the growth of aspherical wind produced during the earliest stage of the outburst. At $t_{rm d}=1.4$~d the H$alpha$ line has a nearly flat-topped profile with weak blue and red peaks at $sim pm 3000$ km s$^{-1}$. This profile can be attributed to a nearly spherical shell, while the asphericity growing on the first night still remains. The wind asphericity is less significant after $t_{rm d}=9$ d.
We present early phase observations in optical and near-infrared wavelengths for the extremely luminous Type Ia supernova (SN Ia) 2009dc. The decline rate of the light curve is $Delta m_{15}(B)=0.65pm 0.03$, which is one of the slowest among SNe Ia.
The peak $V$-band absolute magnitude is $M_{V}=-19.90pm 0.15$ mag even if the host extinction is $A_{V}=0$ mag. It reaches $M_{V}=-20.19pm 0.19$ mag for the host extinction of $A_{V}=0.29$ mag as inferred from the observed Na {sc i} D line absorption in the host. Our $JHK_{s}$-band photometry shows that the SN is one of the most luminous SNe Ia also in near-infrared wavelengths. These results indicate that SN 2009dc belongs to the most luminous class of SNe Ia, like SN 2003fg and SN 2006gz. We estimate the ejected $^{56}$Ni mass of $1.2pm 0.3$ $Msun$ for no host extinction case (or 1.6$pm$ 0.4 M$_{odot}$ for the host extinction of $A_{V}=0.29$ mag). The C {sc ii} $lambda$6580 absorption line keeps visible until a week after maximum, which diminished in SN 2006gz before its maximum brightness. The line velocity of Si {sc ii} $lambda$6355 is about 8000 km s$^{-1}$ around the maximum, being considerably slower than that of SN 2006gz, while comparable to that of SN 2003fg. The velocity of the C {sc ii} line is almost comparable to that of the Si {sc ii}. The presence of the carbon line suggests that thick unburned C+O layers remain after the explosion. SN 2009dc is a plausible candidate of the super-Chandrasekhar mass SNe Ia.
We present optical spectroscopic and photometric observations of Type Ia supernova (SN) 2006X from --10 to +91 days after the $B$-band maximum. This SN exhibits one of the highest expansion velocity ever published for SNe Ia. At premaximum phases, th
e spectra show strong and broad features of intermediate-mass elements such as Si, S, Ca, and Mg, while the O{sc i}$lambda$7773 line is weak. The extremely high velocities of Si{sc ii} and S{sc ii} lines and the weak O{sc i} line suggest that an intense nucleosynthesis might take place in the outer layers, favoring a delayed detonation model. Interestingly, Si{sc ii}$lambda$5972 feature is quite shallow, resulting in an unusually low depth ratio of Si{sc ii}$lambda$5972 to $lambda$6355, $cal R$(Si{sc ii}). The low $cal R$(Si{sc ii}) is usually interpreted as a high photospheric temperature. However, the weak Si{sc iii}$lambda$4560 line suggests a low temperature, in contradiction to the low $cal R$(Si{sc ii}). This could imply that the Si{sc ii}$lambda$5972 line might be contaminated by underlying emission. We propose that $cal R$(Si{sc ii}) may not be a good temperature indicator for rapidly expanding SNe Ia at premaximum phases.
