[Paper Review] The Carnegie Supernova Project II

M. Stritzinger, F. Taddia+20 more|arXiv (Cornell University)|Nov 11, 2019

Gamma-ray bursts and supernovae103 references4 citations

TL;DR

This study presents early optical and near-IR observations of the Type Ib supernova LSQ13abf, discovered within two days of explosion, revealing a distinct early blue peak and post-shock breakout cooling phase. By combining black-body fitting, Arnett model fitting, and post-shock breakout cooling modeling, the authors infer a progenitor star radius of 28.0 ± 7.5 R⊙, a high ejecta mass of 5.94 ± 1.10 M⊙, and an explosion energy of 1.27 ± 0.23 × 10⁵¹ ergs, indicating a massive progenitor likely from a >25 M⊙ zero-age main-sequence star with an extended envelope.

ABSTRACT

Supernova LSQ13abf was discovered soon after explosion by the La Silla-QUEST Survey and followed by the CSP II at optical and near-IR wavelengths. Our analysis indicates LSQ13abf was discovered within two days of explosion and its first 10 days of evolution reveal a B-band light curve with an abrupt drop in luminosity. Contemporaneously, the V-band light curve exhibits a rise towards a first peak and the r- and i-band light curves show no early peak. The early light-curve evolution of LSQ13abf is reminiscent of the post explosion cooling phase observed in the Type Ib SN 2008D, and the similarity between the two objects extends over weeks. Spectroscopically, LSQ13abf resembles SN 2008D with P Cygni He I features that strengthen over time. Spectral energy distributions are constructed from broad-band photometry, and by fitting black-body (BB) functions a UVOIR light curve is constructed, and the underlying BB-temperature and BB-radius profiles are estimated. Explosion parameters are estimated by simultaneously fitting an Arnett model to the UVOIR light curve and the velocity evolution derived from spectral features, and a post-shock breakout cooling model to the first two epochs of the bolometric evolution. This combined model suggests an explosion energy of 1.3x10$^{51}$ ergs, a relatively high ejecta mass of 5.94 M$_{\odot}$, a Ni mass of 0.16 M$_{\odot}$, and a progenitor-star radius of 28.0 R$_{\odot}$. The ejecta mass suggests the origins of LSQ13abf lie with a >25 M$_{\odot}$ ZAMS progenitor and its radius is three and nine times larger than values estimated from the same analysis applied to observations of SNe 2008D and 1999ex, respectively. Alternatively, comparison of hydrodynamical simulations of >20-25 M$_{\odot}$ ZAMS progenitors that evolve to pre-SN envelope masses around 10 M$_{\odot}$ and extended (~100 R$_{\odot}$) envelopes also match the observations of LSQ13abf.

Motivation & Objective

• To constrain the progenitor properties of the Type Ib supernova LSQ13abf using early-time photometric and spectroscopic data.
• To determine the explosion parameters—such as ejecta mass, explosion energy, and ⁵⁶Ni mass—by modeling the early light curve and spectral evolution.
• To investigate the nature of the progenitor star, particularly its radius and structure, using post-shock breakout cooling models.
• To compare the observed early evolution of LSQ13abf with hydrodynamical models of massive He stars in binary systems.
• To explore the implications of the inferred progenitor radius and ejecta mass for current stellar evolution models of massive stars.

Proposed method

• Broad-band photometry across U, B, V, r, i, and near-IR bands was used to construct spectral energy distributions and derive bolometric light curves.
• Black-body (BB) functions were fitted to the spectral energy distributions to estimate the effective temperature and radius evolution of the ejecta.
• A combined modeling approach applied the Arnett model to fit the UVOIR light curve and velocity evolution from spectral features.
• A post-shock breakout cooling model was fitted to the first two epochs of the bolometric light curve to estimate the progenitor radius at explosion.
• Hydrodynamical simulations of 20–25 M⊙ zero-age main-sequence progenitors with extended envelopes were compared to the observed light curves.
• The explosion parameters were derived by simultaneously fitting the Arnett model and the post-shock cooling model to the multi-wavelength data.

Experimental results

Research questions

• RQ1 What is the progenitor radius of LSQ13abf, and how does it compare to other Type Ib SNe with early cooling observations?
• RQ2 What are the explosion energy, ejecta mass, and ⁵⁶Ni mass of LSQ13abf, and what do they imply about the progenitor's initial mass?
• RQ3 How do the early light curves of LSQ13abf, particularly the early blue peak, compare to theoretical models of shock breakout and post-shock cooling?
• RQ4 Can hydrodynamical models of massive He stars in binary systems reproduce the observed early evolution of LSQ13abf?
• RQ5 Why does LSQ13abf exhibit a larger progenitor radius than other well-studied Type Ib SNe such as SN 2008D and SN 1999ex?

Key findings

• LSQ13abf was discovered within 2 days of explosion, capturing the initial post-shock breakout cooling phase.
• The B-band light curve shows an abrupt drop in luminosity during the first ~10 days, while the V-band exhibits a rise to a first peak, indicating a complex early evolution.
• The progenitor star had a radius of 28.0 ± 7.5 R⊙ at explosion, three times larger than estimated for SN 2008D under the same model.
• The ejecta mass was determined to be 5.94 ± 1.10 M⊙, indicating a progenitor with a zero-age main-sequence mass exceeding 25 M⊙.
• The explosion energy was estimated at 1.27 ± 0.23 × 10⁵¹ ergs, with a ⁵⁶Ni mass of 0.16 ± 0.02 M⊙.
• Hydrodynamical models of massive He stars in binary systems with extended envelopes (up to ~100 R⊙) provide a plausible explanation for the observed early light curve and progenitor radius.