Optical observations of type IIP supernova 2004dj: Evidence for the asymmetry of ⁵⁶Ni ejecta

The photometric and spectroscopic observations of nearby type IIP supernova 2004dj are presented. The $^{56}$Ni mass estimated from the light curve is $\approx0.02 M_{\odot}$. This estimate is found to be consistent with the H$\alpha$ luminosity. SN2004dj reveals a strong asymmetry of the H$\alpha$ emission line at the nebular epoch with the shift of the maximum of -1600 km s$^{-1}$. A similar asymmetric component is detected in H$\beta$, [O I] and [Ca II] lines. The line asymmetry is interpreted as a result of the asymmetry of $^{56}$Ni ejecta. The H$\alpha$ profile and its evolution are reproduced in the model of the asymmetric bipolar $^{56}$Ni and spherical hydrogen distributions. The mass of the front $^{56}$Ni jet is comparable to the central component and twice as larger compared to the rear $^{56}$Ni jet. We note that the asymmetric bipolar structure of of $^{56}$Ni ejecta is revealed also by SN1999em, another type IIP supernova.