| Autor: |
Bose, Subhash, Dong, Subo, Kochanek, C S, Stritzinger, M D, Ashall, Chris, Benetti, Stefano, Falco, E, Filippenko, Alexei V, Pastorello, Andrea, Prieto, Jose L, Somero, Auni, Sukhbold, Tuguldur, Zhang, Junbo, Auchettl, Katie, Brink, Thomas G, Brown, J S, Chen, Ping, Fiore, A, Grupe, Dirk, Holoien, T W-S |
| Předmět: |
|
| Zdroj: |
Monthly Notices of the Royal Astronomical Society; May2021, Vol. 503 Issue 3, p3472-3491, 20p |
| Abstrakt: |
ASASSN-18am/SN 2018gk is a newly discovered member of the rare group of luminous, hydrogen-rich supernovae (SNe) with a peak absolute magnitude of MV ≈ −20 mag that is in between normal core-collapse SNe and superluminous SNe. These SNe show no prominent spectroscopic signatures of ejecta interacting with circumstellar material (CSM), and their powering mechanism is debated. ASASSN-18am declines extremely rapidly for a Type II SN, with a photospheric-phase decline rate of ∼6.0 mag (100 d)−1. Owing to the weakening of H i and the appearance of He i in its later phases, ASASSN-18am is spectroscopically a Type IIb SN with a partially stripped envelope. However, its photometric and spectroscopic evolution shows significant differences from typical SNe IIb. Using a radiative diffusion model, we find that the light curve requires a high synthesized 56Ni mass |$M_{\rm Ni} \sim 0.4\, \rm {M_{\odot }}$| and ejecta with high kinetic energy E kin = (7–10) × 1051 erg. Introducing a magnetar central engine still requires |$M_{\rm Ni} \sim 0.3\, \rm {M_{\odot }}$| and E kin = 3 × 1051 erg. The high 56Ni mass is consistent with strong iron-group nebular lines in its spectra, which are also similar to several SNe Ic-BL with high 56Ni yields. The earliest spectrum shows 'flash ionization' features, from which we estimate a mass-loss rate of |$\dot{M}\approx 2\times 10^{-4} \, \rm \rm {M_{\odot }}\,yr^{-1}$|. This wind density is too low to power the luminous light curve by ejecta–CSM interaction. We measure expansion velocities as high as 17 000 |$\rm {\, km\, s^{-1}}$| for Hα, which is remarkably high compared to other SNe II. We estimate an oxygen core mass of 1.8–3.4 M⊙ using the [O i ] luminosity measured from a nebular-phase spectrum, implying a progenitor with a zero-age main-sequence mass of 19–26 M⊙. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
|
