A Previous Transient Consistent with the Location of SN 2009ip Suggests that SN 2009ip is Not a Supernova

ATel #2183; A. A. Miller (UC Berkeley), W. Li (UC Berkeley), P. E. Nugent (LBNL), J. S. Bloom (UC Berkeley), A. V. Filippenko (UC Berkeley), and A. T. Merritt (UC Berkeley)
on 1 Sep 2009; 23:13 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Weidong Li (weidong@astron.berkeley.edu)

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We have examined historical DeepSky (ATEL #1213) images of NGC 7259 and find that a transient consistent with the location of SN 2009ip (Maza et al. 2009; CBET 1928) was present in 2005. Relative to USNO-B1, preliminary photometry yields that the transient was at R ~ 20.6 mag on 2005 Jun 20 (UT dates are used throughout) and R ~ 21.0 mag on 2005 Jul 03. On a stacked image from 2008 Aug 23 we do not detect the transient down to R ~ 22.0 mag. Typical uncertainties when calibrating relative to USNO-B are 0.2 mag.

In a ground-based KAIT image taken on 2009 Aug 30, we measure SN 2009ip to have an unfiltered magnitude of 18.2, which corresponds to an absolute magnitude of M ~ -13.7 mag at the distance of NGC 7259.

We have downloaded an archival HST/WFPC2 image of the field which was taken on 1999 Jun 29 (HST proposal ID 6359). From an astrometric solution between the WFPC2 and KAIT images, we identified a potential progenitor for the transient at

R.A. = 22:23:08.20, Decl. = -28:56:52.6 (J2000.0),

with F606W = 21.8 mag, which corresponds to an absolute magnitude of M ~ -10.1 mag at the distance of NGC 7259.

Given the relatively faint peak absolute magnitude (for a SN) of -13.7 mag, and the recurrent nature of the observed transient, we argue that SN 2009ip is not a SN. Instead, we favor two alternative hypotheses to explain these observations: the transient is associated with an outburst from a luminous blue variable (LBV) star in NGC 7259, or (less likely) the transient is a Galactic cataclysmic variable (CV). Both LBVs and CVs are observed to exhibit multiple outbursts on timescales of years to decades, which could potentially explain the observed transients from 2005 and 2009. Optical spectra, which could potentially discriminate between these two possibilities, are highly encouraged. It is also conceivable, though improbable, that the 2005 outburst created a large amount of dust that now greatly extinguishes a genuine explosion (SN 2009ip); infrared observations could be used to test this hypothesis.