The Blue Supergiant Progenitor of the Supernova Imposter AT~2019krl. (arXiv:2009.13541v2 [astro-ph.SR] UPDATED)

The Blue Supergiant Progenitor of the Supernova Imposter AT~2019krl. (arXiv:2009.13541v2 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Andrews_J/0/1/0/all/0/1">Jennifer E. Andrews</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jencson_J/0/1/0/all/0/1">Jacob E. Jencson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dyk_S/0/1/0/all/0/1">Schuyler D. Van Dyk</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Neustadt_J/0/1/0/all/0/1">Jack M. M. Neustadt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_N/0/1/0/all/0/1">Nathan Smith</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sand_D/0/1/0/all/0/1">David J. Sand</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kreckel_K/0/1/0/all/0/1">K. Kreckel</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kochanek_C/0/1/0/all/0/1">C.S. Kochanek</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Valenti_S/0/1/0/all/0/1">S. Valenti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Strader_J/0/1/0/all/0/1">Jay Strader</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bersten_M/0/1/0/all/0/1">M.C. Bersten</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blanc_G/0/1/0/all/0/1">Guillermo A. Blanc</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bostroem_K/0/1/0/all/0/1">K. Azalee Bostroem</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brink_T/0/1/0/all/0/1">Thomas G. Brink</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Emsellem_E/0/1/0/all/0/1">Eric Emsellem</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Filippenko_A/0/1/0/all/0/1">Alexei V. Filippenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Folatelli_G/0/1/0/all/0/1">Gastón Folatelli</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kasliwal_M/0/1/0/all/0/1">Mansi M. Kasliwal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Masci_F/0/1/0/all/0/1">Frank J. Masci</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McElroy_R/0/1/0/all/0/1">Rebecca McElroy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Milisavljevic_D/0/1/0/all/0/1">Dan Milisavljevic</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Santoro_F/0/1/0/all/0/1">Francesco Santoro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Szalai_T/0/1/0/all/0/1">Tamás Szalai</a>

Extensive archival textit{Hubble Space Telescope}, textit{Spitzer Space
Telescope}, and Large Binocular Telescope imaging of the recent
intermediate-luminosity transient, AT~2019krl in M74, reveal a bright optical
and mid-infrared progenitor star. While the optical peak of the event was
missed, a peak was detected in the infrared with an absolute magnitude of
$M_{4.5,mu {rm m}} = -18.4$ mag, leading us to infer a visual-wavelength
peak absolute magnitude of $-$13.5 to $-$14.5. The pre-discovery light curve
indicated no outbursts over the previous 16,yr. The colors, magnitudes, and
inferred temperatures of the progenitor best match a 13–14 M$_{sun}$ yellow
or blue supergiant (BSG), if only foreground extinction is taken into account,
or a hotter and more massive star, if any additional local extinction is
included. A pre-eruption spectrum of the star reveals strong H$alpha$ and
[N~{sc ii}] emission with wings extending to $pm 2000$,km,s$^{-1}$. The
post-eruption spectrum is fairly flat and featureless with only H$alpha$,
ion{Na}{1}~D, [ion{Ca}{2}], and the ion{Ca}{2} triplet in emission. As in
many previous intermediate-luminosity transients, AT~2019krl shows remarkable
observational similarities to luminous blue variable (LBV) giant eruptions,
SN~2008S-like events, and massive-star mergers. However, the information about
the pre-eruption star favors either a relatively unobscured BSG or a more
extinguished LBV with $M > 20$,M$_{sun}$ likely viewed pole-on.

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