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SN2009ip: New spectrum shows early phases of a luminous Type IIn supernova

ATel #4427; Nathan Smith and Jon Mauerhan (U. Arizona)
on 27 Sep 2012; 09:40 UT
Credential Certification: Nathan Smith (nathans@as.arizona.edu)

Subjects: Optical, Supernovae, Transient, Variables

Referred to by ATel #: 4431, 4434, 4435, 4439, 4454, 4477, 4479

SN 2009ip is developing rapidly. After its rebrightening was discovered in July 2012 (Drake et al. 2012, ATel #4334), we obtained spectra in early September 2012 that showed extremely broad H lines with velocities up to 13,000 km/s, resembling a normal supernova, and we suggested that SN2009ip was transitioning from an LBV eruption to a true core-collapse SN (Smith & Mauerhan, ATel #4412). Although two subsequent reports quickly discounted this possibility (Martin et al. 2012, ATel #4416; Margutti et al. 2012, ATel #4414), SN 2009ip did in fact brighten rapidly to values consistent with a true supernova (Brimacombe et al. 2012, ATel #4423). We obtained additional spectra using the B&C spectrograph on the Bok 2.3 m telescope, taken between UT 04:00-8:00 on Sept 27. The latest spectra reveal that the very broad lines we reported earlier are no longer seen in the spectrum. Instead, we see only narrow lines again in the high luminosity phase. This is consistent with spectra in the early phases of luminous Type IIn supernova (such as SN 2006gy; Smith et al. 2010, ApJ. 709, 856), when the CSM interaction region becomes optically thick and masks the underlying fast SN ejecta. The very broad lines we saw earlier may have marked a brief phase at the onset of the supernova, when the CSM was still transparent and the fast ejecta could be seen. These fast ejecta are now overtaking the slower LBV material ejected previously as we observe a true Type IIn supernova powered by CSM interaction. Rapid followup observations at all wavelengths are encouraged (again), including X-rays.