An impostor among us II: Progenitor, environment, and modelling of AT 2016jbu. (arXiv:2102.09576v2 [astro-ph.HE] UPDATED)

An impostor among us II: Progenitor, environment, and modelling of AT 2016jbu. (arXiv:2102.09576v2 [astro-ph.HE] UPDATED)
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In the second of two papers on the peculiar interacting transient AT 2016jbu,
we present the bolometric lightcurve, identification and analysis of the
progenitor candidate, as well as preliminary modelling to help elucidate the
nature of this event. We identify the progenitor candidate for AT 2016jbu in
quiescence, and find it to be consistent with a $sim$20 M$_{odot}$ yellow
hypergiant surrounded by a dusty circumstellar shell. We see evidence for
significant photometric variability in the progenitor, as well as strong
H$alpha$ emission consistent with pre-existing circumstellar material. The age
of the resolved stellar population surrounding AT 2016jbu, as well as
integral-field unit spectra of the region support a progenitor age of >16 Myr,
again consistent with a progenitor mass of $sim$20 M$_{odot}$. Through a
joint analysis of the velocity evolution of AT 2016jbu, and the photospheric
radius inferred from the bolometric lightcurve, we find that the transient is
consistent with two successive outbursts or explosions. The first outburst
ejected a shell of material with velocity 650 km $s^{-1}$, while the second
more energetic event ejected material at 4500 km $s^{-1}$. Whether the latter
is the core-collapse of the progenitor remains uncertain, as the required
ejecta mass is relatively low (few tenths of M$_{odot}$). We also place a
restrictive upper limit on the ejected $^{56}$Ni mass of <0.016 M$_{odot}$.
Using the BPASS code, we explore a wide range of possible progenitor systems,
and find that the majority of these are in binaries, some of which are
undergoing mass transfer or common envelope evolution immediately prior to
explosion. Finally, we use the SNEC code to demonstrate that the low-energy
explosion of some of these systems together with sufficient CSM can reproduce
the overall morphology of the lightcurve of AT 2016jbu.

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