Detecting stellar outbursts in the decade before massive stars explode as supernovae
Final Report Abstract
Type IIn SNe explode within a dense cloud of circumstellar medium and their progenitor stars are know to be highly variable throughout their lifetime. Leading up to this project I found that most IIn progenitors undergo extremely energetic eruptions in the last months before the SN. Recent models suggest that such a large amount of energy cannot originate from the stellar core, instead the outbursts might be caused by the inspiraling of a compact object. We studied one SN IIn with a bright precursor in detail and showed that it is very similar to a handful of other transients which likely form a separate, uniform subclass. The inspiraling of a binary partner could be one explanation, others include pulsational pair-instability eruptions or wave-heating. The detection of flash-ionization lines reveals that a large fraction of regular SNe II are surrounded by CSM like SNe IIn, but with a much lower CSM mass. Precursor outbursts might eject this material from the stellar surface and indeed a very-low-luminosity outburst was detected prior to a SN II with long-lasting flash features. However, in a follow-up study we found no precursors for 29 nearby SNe of different types indicating that they are faint or rare. We simulate a population of SN progenitors and show that the upcoming LSST experiment will be able to detect tens of progenitor stars and hence also reveal outbursts or other changes in the years before the SN. The estimated masses of SN progenitors are on average lower that expected and it was suggested that high-mass stars collapse into black holes without producing a SN. However, for red supergiants (RSGs) the discrepancy is partially caused by a statistical bias and I find that the luminosities of SN progenitors and RSGs in the Large Magellanic Cloud are consistent with each other. This likely indicates that many massive stars do not turn into RSGs, but lose their envelopes and become stripped stars. However, high-mass stripped progenitors are also rare, potentially because part of the stellar mass forms a compact object. Recently discovered, minute-long flares after the explosion of a stripped star provide direct evidence for the formation of such an object. We monitored 15 short-lived SNe for in total more than 200 hours which will allow us to test whether these objects produce similar flares in the months after their explosion. The data was obtained with the Large Array Survey Telescope, a low-cost array of off-the-shelf telescopes, that we are building in Southern Israel. Such systems allow highcadence monitoring of the nearby universe and can complement large facilities like LSST.
Publications
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SN 2019zrk, a bright SN 2009ip analog with a precursor. Astronomy & Astrophysics, 666, A79.
Fransson, Claes; Sollerman, Jesper; Strotjohann, Nora L.; Yang, Sheng; Schulze, Steve; Barbarino, Cristina; Kool, Erik C.; Ofek, Eran O.; Crellin-Quick, Arien; De, Kishalay; Drake, Andrew J.; Fremling, Christoffer; Gal-Yam, Avishay; Ho, Anna Y. Q. & Kasliwal, Mansi M.
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Search for Supernova Progenitor Stars with ZTF and LSST. The Astrophysical Journal, 960(1), 72.
Strotjohann, Nora L.; Ofek, Eran O.; Gal-Yam, Avishay; Sollerman, Jesper; Chen, Ping; Yaron, Ofer; Zackay, Barak; Rehemtulla, Nabeel; Gris, Phillipe; Masci, Frank J.; Rusholme, Ben & Purdum, Josiah
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A Bias-corrected Luminosity Function for Red Supergiant Supernova Progenitor Stars. The Astrophysical Journal Letters, 964(2), L27.
Strotjohann, Nora L.; Ofek, Eran O. & Gal-Yam, Avishay
