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ZTF18aalrxas: A Type IIb Supernova from a Very Extended Low-mass Progenitor

Fremling, C, Ko, H, Dugas, A, Ergon, M, Sollerman, J, Bagdasaryan, A, Barbarino, C, Belicki, J, Bellm, E, Blagorodnova, N, De, K, Dekany, R, Frederick, S, Gal-Yam, A, Goldstein, DA, Golkhou, VZ, Graham, M, Kasliwal, M, Kowalski, M, Kulkarni, SR , Kupfer, T, Laher, RR, Masci, FJ, Miller, AA, Neill, JD, Perley, DA, Rebbapragada, UD, Riddle, R, Rusholme, B, Schulze, S, Smith, RM, Tartaglia, L, Yan, L and Yao, Y (2019) ZTF18aalrxas: A Type IIb Supernova from a Very Extended Low-mass Progenitor. The Astrophysical Journal Letters, 878 (1). ISSN 2041-8205

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We investigate ZTF18aalrxas, a double-peaked Type IIb core-collapse supernova (SN) discovered during science validation of the Zwicky Transient Facility. ZTF18aalrxas was discovered while the optical emission was still rising toward the initial cooling peak (0.7 mag over 2 days). Our observations consist of multi-band (ultraviolet and optical) light curves (LCs), and optical spectra spanning from ≈0.7 to ≈180 days past the explosion. We use a Monte-Carlo based non-local thermodynamic equilibrium model that simultaneously reproduces both the 56Ni-powered bolometric LC and our nebular spectrum. This model is used to constrain the synthesized radioactive nickel mass (0.17 M ☉) and the total ejecta mass (1.7 M ☉) of the SN. The cooling emission is modeled using semi-analytical extended envelope models to constrain the progenitor radius (790–1050 R ⊙) at the time of explosion. Our nebular spectrum shows signs of interaction with a dense circumstellar medium (CSM), and this spectrum is modeled and analyzed to constrain the amount of ejected oxygen (0.3–0.5 M ☉) and the total hydrogen mass (≈0.15 M ☉) in the envelope of the progenitor. The oxygen mass of ZTF18aalrxas is consistent with a low (12–13 M ☉) zero-age main-sequence mass progenitor. The LCs and spectra of ZTF18aalrxas are not consistent with massive single-star SN Type IIb progenitor models. The presence of an extended hydrogen envelope of low mass, the presence of a dense CSM, the derived ejecta mass, and the late-time oxygen emission can all be explained in a binary model scenario.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical and Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society
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Date Deposited: 05 Jul 2019 09:44
Last Modified: 04 Sep 2021 09:13
DOI or ID number: 10.3847/2041-8213/ab218f
URI: https://researchonline.ljmu.ac.uk/id/eprint/10981
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