SN 2009ip after a decade: the luminous blue variable progenitor is now gone

Abstract

We present new Hubble Space Telescope (HST) imaging photometry for the site of the Type IIn supernova (SN) 2009ip taken almost a decade after explosion. The optical source has continued to fade steadily since the SN-like event in 2012. In the F606W filter, which was also used to detect its luminous blue variable (LBV) progenitor 13 yr before the SN, the source at the position of SN 2009ip is now 1.2 mag fainter than that quiescent progenitor. It is 6–7 mag fainter than the pre-SN outbursts in 2009–2011. This definitively rules out a prediction that the source would return to its previous state after surviving the 2012 event. Instead, the late-time fading matches expectations for a terminal explosion. The source fades at a similar rate in all visual-wavelength filters without significant colour changes, therefore also ruling out the hypothesis of a luminous dust-obscured survivor or transition to a hotter post-LBV survivor. The late-time continuum with steady colour and strong Hα emission detected in a narrow F657N filter are, however, entirely expected for ongoing shock interaction with circumstellar material in a decade-old core-collapse SN. Interestingly, the ultraviolet flux has stayed nearly constant since 2015, supporting previous conjectures that the F275W light traces main-sequence OB stars in an underlying young star cluster. We expect that the visual-wavelength continuum will eventually level off, tracing this cluster light. Without any additional outbursts, it seems prudent to consider the 2012 event as a terminal SN explosion, and we discuss plausible scenarios.