SN 2009ip: an LBV becomes a real supernova

ATel #4412; Nathan Smith, Jon Mauerhan (U. Arizona)
on 22 Sep 2012; 03:43 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Nathan Smith (nathans@as.arizona.edu)

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SN 2009ip was a transient source that was attributed to the eruption of a massive LBV star. Pre-discovery images with HST showed a massive blue progenitor star with a ZAMS mass of about 60 M_sun or more (Smith et al. 2010; Foley et al. 2011) as well as pre-outburst variability consistent with a massive eruptive LBV (Smith et al. 2010), culminating in an eruption with a peak absolute magnitude of -14.5 mag (Smith et al. 2010). It then had a second LBV-like outburst in July 2010 with a peak absolute magnitude of about -14 (Drake et al. 2010; ATel 2897). Drake et al. (2012; ATel #4334) then reported a third brightening of the object on 2012 July 24, which reached an absolute magnitude brighter than -14.5 by August 2012. Foley et al. (2012; ATel #4338) reported that a high-resolution spectrum of SN2009ip in this most recent outburst obtained on 2012 August 26 showed bright Balmer lines with Lorentzian profiles that have FWHM of 640 km/s. This is similar to the spectra of its previous 2009 outburst (Smith et al. 2010; Foley et al. 2011). We obtained low and moderate-resolution spectra using the Steward Observatory B&C spectrograph on the Bok 90" telescope on Kitt Peak on 2012 September 15 and 16, which reveal important changes in the spectrum. In addition to the narrow lines reported previously, the new spectra also show very broad lines typical of a normal Type II supernova. H Balmer lines have strong P Cygni profiles, with a minimum in the absorption at -6000 km/s, and a blue edge to the absorption at -13,000 km/s. Although calibrated photometry was not obtained, the object in the guider camera (red sensitive) appeared brighter than at any previous time compared to nearby field stars. It seems probable that the object discovered as SN 2009ip has suffered multiple LBV eruptions, but has now exploded as a genuine core-collapse supernova of Type IIn. We encourage immediate intense followup observations at all wavelengths.