The progenitor of the supernova imposter AT 2019krl: a SN 2008S-like transient from a blue supergiant

Jennifer Andrews, Jacob E. Jencson, Schuyler D. van Dyk, Jack M.M. Neustadt, Nathan Smith, 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

Research output: Contribution to journalArticlepeer-review

Abstract

For a recent intermediate-luminosity transient, AT 2019krl in M74 (NGC 628) at a distance of only ∼ 9.8 Mpc, extensive archival Hubble Space Telescope (HST), Spitzer Space Telescope, and Large Binocular Telescope (LBT) imaging 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 M4.5 µm = −18.4 mag, leading us to infer a visual-wavelength peak absolute magnitude of −13.5 to −14.5. The light curve from the pre-discovery archival data indicated no outbursts over the previous 16 yr. The colors, magnitudes, and inferred temperatures of the progenitor best match a 13–14 M yellow or blue supergiant, 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 emission having a narrow line core with a width of about 200 km s1 (FWHM) and with wings extending to ± 2000 km s1. The post-eruption spectrum is fairly flat and featureless with only Hα, Na I D, [Ca II], and the Ca II near-infrared triplet in emission, with very little change in the shape of Hα over 120 days. As in many previous intermediate-luminosity transients, AT 2019krl shows remarkable similarities to both massive luminous blue variable (LBV) eruptions and SN 2008S-like events. However, in this case, the information about the pre-eruption star allows us to clearly rule out both a super-AGB star and an electron-capture SN as the origin of this SN 2008S-like event. Instead, the data favor either a relatively unobscured blue supergiant (likely viewed pole-on) or a highly extinguished LBV with M > 20 M, confirming that BSGs or LBVs that may undergo mergers are a viable progenitor pathway to produce SN 2008S-like events.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Sep 28 2020

Keywords

  • Stars: massive, supergiants
  • Supernovae: individual (AT 2019krl)

ASJC Scopus subject areas

  • General

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