Very late-time spectroscopy of SN 2009ip: Constraints on the ongoing H$\alpha$ emission

Abstract

The peculiar supernova (SN) 2009ip is an ambiguous event that spurred many questions regarding its true origins. Here, we present very late-time spectroscopic and photometric observations of SN 2009ip, obtained 9 years (3274 days) after the 2012B outburst. We analyze the H$\alpha$ emission still present in the very late-time spectrum of SN 2009ip. We also obtain photometric measurements in the $r$, $g,$ and $i$ bands. We obtained observations of SN 2009ip on 2021 September 10 with the IMACS instrument at the 6.5 m Magellan Baade Telescope, located at the Las Campanas Observatory. SN 2009ip was detected in the $r$, $g,$ and $i$ bands, with an absolute magnitude in $r$ band of $\sim -8.66$~mag. We show that the source faded significantly since the last observations in these bands. We further show that the very late-time spectrum contains a persistent H$\alpha$ emission, although no other emission lines were detected. We measured a full width at half maximum (FWHM) of $930 \pm 40 \ \textrm{km s}^{-1}$ and luminosity of $\sim 8.0 \times 10^{37} \ \textrm{erg s}^{-1}$ for the H$\alpha$ emission. The luminosity decreased relatively slowly in comparison to the last observations and its fading rate is very similar to other long-living interacting transients, such as SN 2005ip. Finally, we conclude that although these properties could be consistent with a non-regular core-collapse SN, they may also be explained through non-terminal explosion scenarios.