Optical and Infrared Analysis of Type II SN 2006BC

Abstract

We present nebular phase optical imaging and spectroscopy and near/mid-IR imaging of the Type II SN 2006bc. Observations reveal the central wavelength of the symmetric H$\alpha$ line profile to be red-shifted with respect to the host galaxy H$\alpha$ emission by day 325. Such an phenomenon has been argued to result from an asymmetric explosion in the iron-peak elements resulting in a larger mass of $^{56}$Ni and higher excitation of hydrogen on the far side of the SN explosion. We also observe a gradual blue-shifting of this H$\alpha$ peak which is indicative of dust formation in the ejecta. Although showing a normal peak brightness, V $\sim$ -17.2, for a core-collapse SN, 2006bc fades by $\sim$6 mag during the first 400 days suggesting either a relatively low $^{56}$Ni yield, an increase in extinction due to new dust, or both. A short duration flattening of the light curve is observed from day 416 to day 541 suggesting an optical light echo. Based on the narrow time window of this echo, we discuss implications on the location and geometry of the reflecting ISM. With our radiative transfer models, we find an upper limit of 2 x 10$^{-3}$ M$_{\odot}$ of dust around SN 2006bc. In the event that all of this dust were formed during the SN explosion, this quantity of dust is still several orders of magnitude lower than that needed to explain the large quantities of dust observed in the early universe.