* Astronomy

Title: SN 2006tf: Precursor Eruptions and the Optically Thick Regime of Extremely Luminous Type IIn Supernovae
Authors: Nathan Smith, Ryan Chornock, Weidong Li, Mohan Ganeshalingam, Jeffrey M. Silverman, Ryan J. Foley, Alexei V. Filippenko, Aaron J. Barth

SN2006tf is the third most luminous supernova (SN) discovered so far, after SN2005ap and SN2006gy. SN2006tf is valuable because it provides a link between two regimes: (1) luminous type IIn's powered by emission directly from interaction with circumstellar material (CSM), and (2) the most extremely luminous SNe where the CSM interaction is so optically thick that energy must diffuse out from an opaque shocked shell. As SN2006tf evolves, it transitions from the second to the first. This link suggests that the range in properties of the most luminous SNe are largely determined by the amount and speed of H-rich material ejected shortly before they explode. The total energy radiated by SN2006tf was about 7e50 ergs. If the bulk of this came from the thermalisation of shock energy, then the star needs to have ejected 18 Msun in the 4--8 yr before core collapse, and another 2--6 Msun in the decades before that. Alternatively, decay from an initial 56Ni mass of 4.5 Msun could also power the light curve. In either case, a Type Ia explosion or core collapse in a moderately massive star are excluded. From the H-alpha line profile, we derive a blast-wave speed of 2,000 km/s that does not decelerate with time, and from the narrow P Cygni absorption we deduce that the progenitor's wind speed was 190 km/s. This is reminiscent of the wind speeds of LBVs, but not of red supergiants or WR stars. We propose that like SN2006gy, SN2006tf marked the death of a very massive star that retained a hydrogen envelope, and suffered extreme LBV-like mass loss in the decades before it exploded.

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