The Blue Supergiant Progenitor of the Supernova Imposter at 2019krl

Jennifer E. Andrews, Jacob E. Jencson, Schuyler D. Van Dyk, Nathan Smith, Jack M.M. Neustadt, David J. Sand, K. Kreckel, C. S. Kochanek, S. Valenti, Jay Strader, M. C. Bersten, Guillermo A. Blanc, K. Azalee Bostroem, Thomas G. Brink, Eric Emsellem, Alexei V. Filippenko, Gastón Folatelli, Mansi M. Kasliwal, Frank J. Masci, Rebecca McElroyDan Milisavljevic, Francesco Santoro, Tamás Szalai

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10 Scopus citations


Extensive archival Hubble Space Telescope, 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 μm = -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 o˙ 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 Hα and [N ii] emission with wings extending to 2000 km s-1. The post-eruption spectrum is fairly flat and featureless with only Hα, Na i D, [Ca ii], and the Ca ii 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 Mo˙ likely viewed pole-on.

Original languageEnglish (US)
Article number63
JournalAstrophysical Journal
Issue number2
StatePublished - Aug 20 2021

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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