Abstract
We present the first non-LTE time-dependent radiative-transfer simulations of supernovae (SNe) II-Plateau (II-P) covering both the photospheric and nebular phases, from ~10 to >~1000d after the explosion, and based on 1.2B piston-driven ejecta produced from a 15Msun and a 25Msun non-rotating solar-metallicity star. The radial expansion of the gradually cooling photosphere gives rise to a near-constant luminosity up to >~100d after explosion. The photosphere remains in the outer 0.5Msun of the ejecta for up to ~50d after explosion. As the photosphere reaches the edge of the helium core, the SN luminosity drops by an amount mitigated by the progenitor radius and the 56Ni mass. Synthetic light-curves exhibit a bell-shape morphology, evolving faster for more compact progenitors, and with an earlier peak and narrower width in bluer filters. UV and U-band fluxes are very sensitive to line-blanketing, the metallicity, and the adopted model atoms. During the recombination epoch synthetic spectra are dominated by HI and metal lines, and are largely insensitive to the differing H/He/C/N/O composition of our two progenitor stars. In contrast, synthetic nebular-phase spectra reveal a broader/stronger OI doublet line in the higher-mass progenitor model, reflecting the larger masses of oxygen and nickel that are ejected. Our simulations overestimate the typical luminosity and the visual rise time of standard SNe II-P, likely a consequence of our progenitor stars being too big and/or too hydrogen rich. Comparison of our simulations with photospheric-phase observations of SN1999em of the same color are satisfactory. Our neglect of non-thermal processes leads to a fast disappearance of continuum radiation and Balmer-line emission at the end of the plateau phase. With the exception of HI lines, our nebular spectra show a striking similarity to contemporaneous observations of SN1999em.
Highlights
Supernovae (SNe) II-Plateau (II-P) are the most represented SN type (Cappellaro et al 1997; Smartt et al 2009)
The near uniform photospheric composition with time during the photospheric phase, as well as the modest composition contrast between the hydrogen envelopes of RSG models, highlights the difficulty of constraining the progenitor identity with photosphericphase spectra. It partially explains the uniformity of SNe II-P spectra, which tend to show lines from the same ions, with the same strength and shapes, and generally only differing in width (Dessart & Hillier 2006; Dessart et al 2008). This suggests that differences between SNe II-P are difficult to extract after the onset of recombination in the photospheric phase
We find stronger line blanketing in simulations based on model s15e12iso at the recombination epoch, in particular associated with the treatment of Sc II, Cr II, Fe I and Ni II, which leads to a reduction of the already faint UB-band magnitudes by 0.5 mag
Summary
Supernovae (SNe) II-Plateau (II-P) are the most represented SN type (Cappellaro et al 1997; Smartt et al 2009). An attractive and more physically consistent alternative is to use radiation hydrodynamics up to a few days after shock-breakout, when acceleration terms are sizeable, and switch to a more sophisticated radiative-transfer treatment on a nonaccelerating ejecta (Eastman et al 1994; Kasen & Woosley 2009; Dessart & Hillier 2010) This permits a more detailed treatment of line blanketing, departures from LTE and the dependence of the radiation field on frequency, angle and time. Because of the huge computational expense of this endeavour, we focus on only two ejecta produced from the explosion of stars with mainsequence masses of 15 and 25 M , and characterized by an explosion energy of 1.2 B (Woosley, private communication; Woosley & Heger 2007) We use these simulations to describe fundamental properties of the SN gas and light, with special emphasis on spectra which have not previously been computed with this level of physical consistency in this context.
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