SN 2007uy - metamorphosis of an aspheric Type Ib explosion

The supernovae (SNe) of Type Ibc are rare and the detailed characteristics of these explosions have been studied only for a few events. Unlike Type II SNe, the progenitors of Type Ibc have never been detected in pre-explosion images. So, to understand the nature of their progenitors and the characteristics of the explosions, investigation of proximate events is necessary. Here we present the results of multiwavelength observations of Type Ib SN 2007uy in the nearby (∼29.5 Mpc) galaxy NGC 2770. Analysis of the photometric observations revealed this explosion as an energetic event with peak absolute R-band magnitude −18.5 ± 0.16, which is about 1 mag brighter than the mean value (−17.6 ± 0.6) derived for well observed Type Ibc events. The SN is highly extinguished, E(B − V) = 0.63 ± 0.15 mag, mainly due to foreground material present in the host galaxy. From optical light curve modelling we determine that about 0.3 M⊙ radioactive ⁵⁶Ni is produced and roughly 4.4 M⊙ material is ejected during this explosion with liberated energy ∼15 × 10⁵¹ erg, indicating the event to be an energetic one. Through optical spectroscopy, we have noticed a clear aspheric evolution of several line-forming regions, but no dependency of asymmetry is seen on the distribution of ⁵⁶Ni inside the ejecta. The SN shock interaction with the circumstellar material is clearly noticeable in radio follow-up, presenting a synchrotron self-absorption dominated light curve with a contribution of free–free absorption during the early phases. Assuming a Wolf–Rayet (WR) star, with wind velocity ≳ 10³ km s^{− 1}, as a progenitor, we derive a lower limit to the mass-loss rate inferred from the radio data as Ṁ ≳ 2.4 × 10⁻⁵ M⊙ yr⁻¹, which is consistent with the results obtained for other Type Ibc SNe bright at radio frequencies.