Constraints on pre-SN outbursts from the progenitor of SN 2023ixf using the Large Binocular Telescope

Abstract

The progenitor of SN 2023ixf was a $\sim$10$^{4.8}$ to $10^{5.0}\rm ~L_\odot$ star ($\sim$9 to $14 \rm~M_\odot$ at birth) obscured by a dusty $\dot{M} \simeq 10^{-5} \rm~M_\odot~yr^{-1}$ wind with a visual optical depth of $\tau_V \simeq 13$. This is required by the progenitor SED, the post-SN X-ray and H$\alpha$ luminosities, and the X-ray column density estimates. In Large Binocular Telescope (LBT) data spanning 5600 to 400 d before the SN, there is no evidence for optical variability at the level of $\sim$10$^3\rm~L_\odot$ in $R$ band, roughly 3 times the predicted luminosity of the obscured progenitor. This constrains direct observation of any pre-SN optical outbursts where there are LBT observations. However, models of the effects of any pre-SN outburst on the dusty wind show that an outburst of essentially any duration exceeding $\sim$5 times the luminosity of the progenitor would have detectable effects on the dust optical depth for decades. While the dust obscuration here is high, all red supergiants have dusty winds, and the destruction (or formation) of dust by even short-lived transients will always have long term effects on the observed brightness of the star because changes in the dust optical depths after a luminous transient occur very slowly.