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

June 2019 • 2019ApJ...878L...5F

Authors • 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, D. A. • Golkhou, V. Z. • Graham, M. • Kasliwal, M. • Kowalski, M. • Kulkarni, S. R. • Kupfer, T. • Laher, R. R. • Masci, F. J. • Miller, A. A. • Neill, J. D. • Perley, D. A. • Rebbapragada, U. D. • Riddle, R. • Rusholme, B. • Schulze, S. • Smith, R. M. • Tartaglia, L. • Yan, Lin • Yao, Y.

Abstract • 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.


IPAC Authors

Frank Masci

Senior Scientist

Ben Rusholme

Chief Engineer