| 1. |
- Bruch, Rachel J., et al.
(författare)
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The Prevalence and Influence of Circumstellar Material around Hydrogen-rich Supernova Progenitors
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 952:2
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Tidskriftsartikel (refereegranskat)abstract
- Narrow transient emission lines (flash-ionization features) in early supernova (SN) spectra trace the presence of circumstellar material (CSM) around the massive progenitor stars of core-collapse SNe. The lines disappear within days after the SN explosion, suggesting that this material is spatially confined, and originates from enhanced mass loss shortly (months to a few years) prior to the explosion. We performed a systematic survey of H-rich (Type II) SNe discovered within less than 2 days from the explosion during the first phase of the Zwicky Transient Facility survey (2018–2020), finding 30 events for which a first spectrum was obtained within <2 days from the explosion. The measured fraction of events showing flash-ionization features (>36% at the 95% confidence level) confirms that elevated mass loss in massive stars prior to SN explosion is common. We find that SNe II showing flash-ionization features are not significantly brighter, nor bluer, nor more slowly rising than those without. This implies that CSM interaction does not contribute significantly to their early continuum emission, and that the CSM is likely optically thin. We measured the persistence duration of flash-ionization emission and find that most SNe show flash features for ≈5 days. Rarer events, with persistence timescales >10 days, are brighter and rise longer, suggesting these may be intermediate between regular SNe II and strongly interacting SNe IIn.
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| 2. |
- Karamehmetoglu, Emir, 1992-, et al.
(författare)
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A population of Type Ibc supernovae with massive progenitors Broad lightcurves not uncommon in (i)PTF
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
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Tidskriftsartikel (refereegranskat)abstract
- If high-mass stars (≳20 − 25 M⊙) are the progenitors of stripped-envelope (SE) supernovae (SNe), their massive ejecta should lead to broad, long-duration lightcurves. Instead, literature samples of SE SNe have reported relatively narrow lightcurves corresponding to ejecta masses between 1 − 4 M⊙ that favor intermediate-mass progenitors (≲20 − 25 M⊙). Working with an untargeted sample from a single telescope to better constrain their rates, we searched the Palomar Transient Factory (PTF) and intermediate-PTF (iPTF) sample of SNe for SE SNe with broad lightcurves. Using a simple observational marker of g- or r-band lightcurve stretch compared to a template to measure broadness, we identified eight significantly broader Type Ibc SNe after applying quantitative sample selection criteria. The lightcurves, broad-band colors, and spectra of these SNe are found to evolve more slowly relative to typical Type Ibc SNe, proportional with the stretch parameter. Bolometric lightcurve modeling and their nebular spectra indicate high ejecta masses and nickel masses, assuming radioactive decay powering. Additionally, these objects are preferentially located in low-metallicity host galaxies with high star formation rates, which may account for their massive progenitors, as well as their relative absence from the literature. Our study thus supports the link between broad lightcurves (as measured by stretch) and high-mass progenitor stars in SE SNe with independent evidence from bolometric lightcurve modeling, nebular spectra, host environment properties, and photometric evolution. In the first systematic search of its kind using an untargeted sample, we used the stretch distribution to identify a higher than previously appreciated fraction of SE SNe with broad lightcurves (∼13%). Correcting for Malmquist and lightcurve duration observational biases, we conservatively estimate that a minimum of ∼6% of SE SNe are consistent with high-mass progenitors. This result has implications for the progenitor channels of SE SNe, including late stages of massive stellar evolution, the origin of the observed oxygen fraction in the universe, and formation channels for stellar-mass black holes.
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| 3. |
- Karamehmetoglu, Emir, 1992-
(författare)
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Looking for the high-mass progenitors of stripped-envelope supernovae
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stripped-envelope supernovae were thought to be the explosions of very massive stars (& 20 M) that lost their outer layers of hydrogen and/or helium in strong stellar winds. However, recent studies have highlighted that most stripped-envelope supernovae seem to be arising from rela- tively lower-mass progenitor stars in the 12 20 M(sun) range, creating a mystery about the fate of the higher-mass stars. In this licentiate thesis, we review our knowledge of stripped-envelope supernovae, and present the astrophysical problem of their missing high-mass progenitors. The thesis focuses on observations of unique and rare stripped-envelope supernovae classified with modern optical surveys such as the intermediate Palomar Transient Factory (iPTF) and the Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO). In these surveys we have discovered stripped-envelope supernovae with long-lasting broad lightcurves, which are thought to be a marker for highly massive (& 20 M[sun]) progenitor stars. Despite this exciting association, there are only a handful of existing examples of stripped- envelope supernovae with broad lightcurves published in the literature, not numerous enough to account for the missing high-mass stars.During our efforts, the first object we focused on was OGLE-2014-SN-131, a long-lasting supernova in the southern sky initially classified by PESSTO. We re-classified it as a supernova Type Ibn interacting with a helium-rich circumstellar environment. Unlike all other Type Ibn’s in the literature, OGLE-2014-SN-131 was found to have a long rise-time and large lightcurve broadness. By modeling its bolometric lightcurve, we concluded that OGLE-2014-SN-131 must have had an unusually massive progenitor star. Furthermore, since an ordinary radioactive- decay model could not reproduce the lightcurve, we investigated both a magnetar and circum- stellar interaction as potential powering scenarios and favored the latter due to the signatures of interaction present in the spectra. Next, we looked for similar objects in the supernova dataset of the iPTF, which contains over 200 stripped-envelope supernovae. Searching in a sub-sample of 100 well-observed supernovae, we identified 11 to have unusually broad lightcurves. We also constrained the distribution of lightcurve broadness for iPTF stripped-envelope supernovae. The 11 with broad lightcurves will be studied carefully in a forthcoming paper. The first part of this forthcoming paper, which describes the careful statistical identification of these super-novae, is included in this thesis. In it we identify that 10% of the iPTF stripped-envelope supernova sample have broad lightcurves, which a surprisingly high fraction given their rarity in the published literature. Finally, we evaluate whether our estimate of the fraction of broad stripped-envelope supernovae could help explain the missing high-mass progenitors, and con- clude that they can only be a small fraction of the missing high-mass progenitors.
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