The Unprecedented Third Outburst of SN 2009ip: A Luminous Blue Variable Becomes a Supernova

Jon C. Mauerhan, Nathan Smith, Alexei Filippenko, Kyle Blanchard, Peter Blanchard, Chadwick F. E. Casper, S. Bradley Cenko, Kelsey I. Clubb, Daniel Cohen, Gary Li, and Jeffrey M. Silverman

University of Arizona, Steward Observatory;
UC Berkeley.

Some reports of supernova (SN) discoveries turn out not to be true core-collapse explosions. One such case was SN 2009ip, which was recognized to be a luminous blue variable (LBV) eruption. This source had a massive (50-80 Msun) hot progenitor star identified in pre-explosion data, it had documented evidence of pre-outburst variability, and it was subsequently discovered to have a 2nd outburst in 2010. This same source rebrightened again in 2012, and early spectra showed the same narrow-line profiles as before, suggesting another LBV-like eruption. We present new photometry and spectroscopy of SN 2009ip, indicating that its 3rd observed outburst in under 4 years appears to have transitioned into a genuine SN. The most striking discovery in these data is that unlike previous reports, the spectrum exhibited Balmer lines with very broad P-Cygni profiles characteristic of normal Type II supernovae (SNe II), in addition to narrow emission lines seen in SNe IIn and LBVs. Emission components have FWHM~8000 km/s, while the P-Cygni absorption component has blue wings extending to about -13,000 km/s. These features are typical of Type II SNe, but have never been seen in a nonterminal LBV-like eruption. Initially, the peak absolute magnitude of M_V~ -14.5 seemed fainter than that of normal SNe and faded much more rapidly. However, the source quickly brightened again to M_R=-17.6 mag, indicating that it is indeed a true SN. In this bright phase, the broad lines mostly disappeared, and the spectrum became dominated by broad-winged Lorentzian profiles of H-alpha and HeI that are characteristic of the early optically thick phases of luminous SNe IIn. We conclude that the most recent 2012 outburst of SN 2009ip is most likely a true core-collapse SN IIn that was initially faint, but then rapidly achieved high luminosities, as a result of interaction with circumstellar material (abridged).

Reference: Mauerhan et al. 2012, arXiv:1209.6320
Status: Manuscript has been submitted


Comments: Submitted to MNRAS on 2012 September 27
8 pages, 5 figures