The Blue Supergiant Progenitor of the Supernova Imposter AT 2019krl

August 2021 • 2021ApJ...917...63A

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

Abstract • 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 M4.5 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 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 M likely viewed pole-on.


IPAC Authors

Frank Masci

Senior Scientist

Schuyler Van Dyk

Senior Scientist