Supernova PTF 12glz: a possible shock driven through an aspherical wind

Wind supernovae - also called “type IIn”- are supernovae (SNe) whose spectrum shows bright and narrow Balmer emission lines. Rather than a signature of the explosion itself, this spectral specificity is believed to result from the interaction between the fast ejecta and a dense, Hydrogen-rich, circumstellar medium which surrounded the star in the months and years prior to its explosive death. In the last decade, the physical picture governing SNe IIn explosions and the wider family of “interacting” SNe - SNe whose radiation can be partially or completely accounted for by the ejecta crashing into a dense surrounding medium – has aroused a lot of interest. Studying wind-SNe provides unique clues about the latest stages of stellar evolution and the opportunity to learn about the mass and history of the circumstellar medium surrounding massive stars shortly before their death.  Some of the questions that remain unsolved may soon be unveiled by the Zwicky Transient Facility (ZTF), a new time-domain survey based at the Palomar Observatory, which had its first light in November and in which the Weizmann Institute is actively involved.

We present our recent work on the Supernova PTF12glz, discovered and monitored in near-UV and R band as part of a joint GALEX and PTF (Palomar Transient Factory) campaign. PTF 12glz is among the most energetic Type IIn supernovae observed to date and shows a puzzling peculiarity: a phase of radial expansion taking place at early times, while the freely expanding ejecta are presumably masked by the optically thick circumstellar medium (CSM) and before any spectroscopic signature of expending ejecta appears in the spectrum. We propose a geometrical solution to this puzzle, involving an aspherical structure of the CSM around PTF 12glz. Exploring the expected effect of deviation from spherically symmetric CSM on the observables of interacting supernovae is all the more important since aspherical clouds of CSM around mass-ejecting stars seem to be common, e.g., in stars like η-Carinae that have been proposed as SNe IIn progenitors.