分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: With the advent of high cadence, all-sky automated surveys, supernovae (SNe) are now discovered closer than ever to their dates of explosion. However, young pre-maximum light follow-up spectra of Type Ic supernovae (SNe Ic), probably arising from the most stripped massive stars, remain rare despite their importance. In this paper we present a set of 49 optical spectra observed with the Las Cumbres Observatory through the Global Supernova Project for 6 SNe Ic, including a total of 17 pre-maximum spectra, of which 8 are observed more than a week before V-band maximum light. This dataset increases the total number of publicly available pre-maximum light SN Ic spectra by 25% and we provide publicly available SNID templates that will significantly aid in the fast identification of young SNe Ic in the future. We present detailed analysis of these spectra, including Fe II 5169 velocity measurements, O I 7774 line strengths, and continuum shapes. We compare our results to published samples of stripped supernovae in the literature and find one SN in our sample that stands out. SN 2019ewu has a unique combination of features for a SN Ic: an extremely blue continuum, high absorption velocities, a P-cygni shaped feature almost 2 weeks before maximum light that TARDIS radiative transfer modeling attributes to C II rather than H$\alpha$, and weak or non-existent O I 7774 absorption feature until maximum light.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We present JWST near- and mid-infrared spectroscopic observations of the nearby normal Type Ia supernova SN 2021aefx in the nebular phase at $+255$ days past maximum light. Our Near Infrared Spectrograph (NIRSpec) and Mid Infrared Instrument (MIRI) observations, combined with ground-based optical data from the South African Large Telescope (SALT), constitute the first complete optical $+$ NIR $+$ MIR nebular SN Ia spectrum covering 0.3$-$14 $\mu$m. This spectrum unveils the previously unobserved 2.5$-$5 $\mu$m region, revealing strong nebular iron and stable nickel emission, indicative of high-density burning that can constrain the progenitor mass. The data show a significant improvement in sensitivity and resolution compared to previous Spitzer MIR data. We identify numerous NIR and MIR nebular emission lines from iron-group elements and as well as lines from the intermediate-mass element argon. The argon lines extend to higher velocities than the iron-group elements, suggesting stratified ejecta that are a hallmark of delayed-detonation or double-detonation SN Ia models. We present fits to simple geometric line profiles to features beyond 1.2 $\mu$m and find that most lines are consistent with Gaussian or spherical emission distributions, while the [Ar III] 8.99 $\mu$m line has a distinctively flat-topped profile indicating a thick spherical shell of emission. Using our line profile fits, we investigate the emissivity structure of SN 2021aefx and measure kinematic properties. Continued observations of SN 2021aefx and other SNe Ia with JWST will be transformative to the study of SN Ia composition, ionization structure, density, and temperature, and will provide important constraints on SN Ia progenitor and explosion models.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Type Iax supernovae (SN Iax) are the largest known class of peculiar white dwarf supernovae, distinct from normal type Ia supernovae (SN Ia). The unique properties of SN Iax, especially their strong photospheric lines out to extremely late-times, allow us to model their optical spectra and derive physical parameters for the long-lasting photosphere. We present an extensive spectral timeseries, including 21 new spectra, of SN Iax 2014dt from +11 to +562 days after maximum light. We are able to reproduce the entire timeseries with a self-consistent, nearly unaltered deflagration explosion model from Fink et al. (2014) using TARDIS, an open-source radiative transfer code (Kerzendorf & Sim 2014; Kerzendorf et al. 2023). We find that the photospheric velocity of SN 2014dt slows its evolution between +64 and +148 days, which closely overlaps the phase when we see SN 2014dt diverge from the normal spectral evolution of SN Ia (+90 to +150 days). The photospheric velocity at these epochs, ~ 400--1000 km s$^{-1}$, may demarcate a boundary within the ejecta below which the physics of SN Iax and normal SN Ia differ. Our results suggest that SN 2014dt is consistent with a weak deflagration explosion model that leaves behind a bound remnant and drives an optically thick, quasi-steady-state wind creating the photospheric lines at late times. The data also suggest that this wind may weaken at epochs past +450 days, perhaps indicating a depleted radioactive power source.